Wulfila Gronenberg

Interests

Research

Neuronal control of complex animal behavior; multimodal information processing and brain plasticitycomparative neuroethology,brain and behavior of insects (Hymenoptera: bees, ants, and wasps) and some arachnids (spiders and their kin).

Courses

Scholarly Contributions

Chapters

• Milde, J. J., Milde, J. J., Gronenberg, W., Strausfeld, N. J., & Strausfeld, N. J. (1992). The Head-Neck System of the Blowfly Calliphora: 2. Functional Organization and Comparisons with the Sphinx Moth Manduca sexta. In The Head-Neck Sensory Motor System$ The Head-Neck Sensory Motor System Alain Berthoz, Werner Graf, and P. P. Vidal. Oxford University Press. doi:10.1093/ACPROF:OSO/9780195068207.003.0007

Journals/Publications

• Gronenberg, W., Aksamit, I. C., Dorigão- Guimarãe, F., & Keating Godfrey, R. (2024).

   Brain size scaling through development in the whitelined sphinx moth (Hyles lineata) shows mass and cell number comparable to flies, bees, and wasps.

  . Arthropod Structure & Development, 78, 1-9 (ASD_101329). doi:https://doi.org/10.1016/j.asd.2023.101329
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  Brain size and neuron numbers in larval and adult moths Hyles lineata
• Oberski, J. T., Hernandez-rivera, J., Gronenberg, W., Godfrey, R. K., Givens, C., & Allmark, T. (2021). Olfactory System Morphology Suggests Colony Size Drives Trait Evolution in Odorous Ants (Formicidae: Dolichoderinae). Frontiers in Ecology and Evolution, 9. doi:10.3389/fevo.2021.733023
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  In social insects colony fitness is determined in part by individual worker phenotypes. Across ant species, colony size varies greatly and is thought to affect worker trait variation in both proximate and ultimate ways. Little is known about the relationship between colony size and worker trait evolution, but hypotheses addressing the role of social structure in brain evolution suggest workers of small-colony species may have larger brains or larger brain regions necessary for complex behaviors. In previous work on odorous ants (Formicidae: Dolichoderinae) we found no correlation between colony size and these brain properties, but found that relative antennal lobe size scaled negatively with colony size. Therefore, we now test whether sensory systems scale with colony size, with particular attention to olfactory components thought to be involved in nestmate recognition. Across three species of odorous ants, Forelius mccooki, Dorymyrmex insanus, and D. bicolor, which overlap in habitat and foraging ecology but vary in colony size, we compare olfactory sensory structures, comparing those thought to be involved in nestmate recognition. We use the visual system, a sensory modality not as important in social communication in ants, as a control comparison. We find that body size scaling largely explains differences in eye size, antennal length, antennal sensilla density, and total number of olfactory glomeruli across these species. However, sensilla basiconica and olfactory glomeruli in the T6 cluster of the antennal lobe, structures known to be involved in nestmate recognition, do not follow body size scaling observed for other structures. Instead, we find evidence from the closely related Dorymyrmex species that the larger colony species, D. bicolor, invests more in structures implicated in nestmate recognition. To test for functional consequences, we compare nestmate and non-nestmate interactions between these two species and find D. bicolor pairs of either type engage in more interactions than D. insaus pairs. Thus, we do not find evidence supporting a universal pattern of sensory system scaling associated with changes in colony size, but hypothesize that observed differences in the olfactory components in two closely related Dorymyrmex species are evidence of a link between colony size and sensory trait evolution.
• Sinakevitch, I., Long, S. M., & Gronenberg, W. (2021). The central nervous system of whip spiders (Amblypygi): Large mushroom bodies receive olfactory and visual input.. The Journal of comparative neurology, 529(7), 1642-1658. doi:10.1002/cne.25045
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  Whip spiders (Amblypygi) are known for their nocturnal navigational abilities, which rely on chemosensory and tactile cues and, to a lesser degree, on vision. Unlike true spiders, the first pair of legs in whip spiders is modified into extraordinarily long sensory organs (antenniform legs) covered with thousands of mechanosensory, olfactory, and gustatory sensilla. Olfactory neurons send their axons through the leg nerve into the corresponding neuromere of the central nervous system, where they terminate on a particularly large number (about 460) of primary olfactory glomeruli, suggesting an advanced sense of smell. From the primary glomeruli, olfactory projection neurons ascend to the brain and terminate in the mushroom body calyx on a set of secondary olfactory glomeruli, a feature that is not known from olfactory pathways of other animals. Another part of the calyx receives visual input from the secondary visual neuropil (the medulla). This calyx region is composed of much smaller glomeruli ("microglomeruli"). The bimodal input and the exceptional size of their mushroom bodies may support the navigational capabilities of whip spiders. In addition to input to the mushroom body, we describe other general anatomical features of the whip spiders' central nervous system.
• Swartzlander, M., Gronenberg, W., & Godfrey, R. K. (2021). Allometric analysis of brain cell number in Hymenoptera suggests ant brains diverge from general trends.. Proceedings. Biological sciences, 288(1947), 20210199. doi:10.1098/rspb.2021.0199
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  Many comparative neurobiological studies seek to connect sensory or behavioural attributes across taxa with differences in their brain composition. Recent studies in vertebrates suggest cell number and density may be better correlated with behavioural ability than brain mass or volume, but few estimates of such figures exist for insects. Here, we use the isotropic fractionator (IF) method to estimate total brain cell numbers for 32 species of Hymenoptera spanning seven subfamilies. We find estimates from using this method are comparable to traditional, whole-brain cell counts of two species and to published estimates from established stereological methods. We present allometric scaling relationships between body and brain mass, brain mass and nuclei number, and body mass and cell density and find that ants stand out from bees and wasps as having particularly small brains by measures of mass and cell number. We find that Hymenoptera follow the general trend of smaller animals having proportionally larger brains. Smaller Hymenoptera also feature higher brain cell densities than the larger ones, as is the case in most vertebrates, but in contrast with primates, in which neuron density remains rather constant across changes in brain mass. Overall, our findings establish the IF as a useful method for comparative studies of brain size evolution in insects.
• Gronenberg, W., & Godfrey, R. K. (2020). Linking Colony Size with Foraging Behavior and Brain Investment in Odorous Ants (Formicidae: Dolichoderinae).. Brain, behavior and evolution, 95(1), 15-24. doi:10.1159/000504643
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  Superorganisms represent a unique level of biological organization in which the phenotype of the reproductive unit, the colony, results from traits expressed at the level of individual workers. Because body size scaling has important consequences for cell diversity and system complexity in solitary organisms, colony size is a trait of particular interest in superorganism evolution. In some instances, division of labor and worker polymorphism scale with colony size, but in general little is known about how colony size drives differences in individual-level behavior or neural traits. Ants represent the greatest diversity of superorganisms and provide a manner of natural experiment to test trends in trait evolution across multiple instances of colony size expansion. In this study, we control for environmental differences and worker size polymorphism to test if colony size correlates with measures of foraging behavior and brain size in dolichoderine ants. We present data from 3 species ranked by colony size. Our results suggest colony size correlates with measures of exploratory behavior and brain investment, with small-colony ants showing higher exploratory drive and faster exploration rate than the larger colony species, and greater relative investment in the primary olfactory brain region, the antennal lobe, than the larger colony species.
• Riveros, A. J., Papaj, D. R., Leonard, A. S., & Gronenberg, W. (2020). Learning of bimodal versus unimodal signals in restrained bumble bees.. The Journal of experimental biology, 223(Pt 10), jeb220103. doi:10.1242/jeb.220103
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  Similar to animal communication displays, flowers emit complex signals that attract pollinators. Signal complexity could lead to higher cognitive load for pollinators, impairing performance, or might benefit them by facilitating learning, memory and decision making. Here, we evaluated learning and memory in foragers of the bumble bee Bombus impatiens trained to simple (unimodal) versus complex (bimodal) signals under restrained conditions. Use of a proboscis extension response protocol enabled us to control the timing and duration of stimuli presented during absolute and differential learning tasks. Overall, we observed broad variation in performance under the two conditions, with bees trained to compound bimodal signals learning and remembering as well as, better than or more poorly than bees trained to unimodal signals. Interestingly, the outcome of training was affected by the specific colour-odour combination. Among unimodal stimuli, the performance with odour stimuli was higher than with colour stimuli, suggesting that olfactory signals played a more significant role in the compound bimodal condition. This was supported by the fact that after 24 h, most bimodal-treatment bees responded to odour but not visual stimuli. We did not observe differences in latency of response, suggesting that signal composition affected decision accuracy, not speed. We conclude that restrained bumble bee workers exhibit broad variation of responses to bimodal stimuli and that components of the bimodal signal may not be used equivalently. The analysis of bee performance under restrained conditions enables accurate control of the multimodal stimuli provided to individuals and to study the interaction of individual components within a compound.
• Riveros, A. J., Papaj, D. R., Leonard, A. S., & Gronenberg, W. (2020). Learning of bimodal versus unimodal signals in restrained bumble bees.. The Journal of experimental biology, 223(Pt 10). doi:10.1242/jeb.220103
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  Similar to animal communication displays, flowers emit complex signals that attract pollinators. Signal complexity could lead to higher cognitive load for pollinators, impairing performance, or might benefit them by facilitating learning, memory and decision making. Here, we evaluated learning and memory in foragers of the bumble bee Bombus impatiens trained to simple (unimodal) versus complex (bimodal) signals under restrained conditions. Use of a proboscis extension response protocol enabled us to control the timing and duration of stimuli presented during absolute and differential learning tasks. Overall, we observed broad variation in performance under the two conditions, with bees trained to compound bimodal signals learning and remembering as well as, better than or more poorly than bees trained to unimodal signals. Interestingly, the outcome of training was affected by the specific colour-odour combination. Among unimodal stimuli, the performance with odour stimuli was higher than with colour stimuli, suggesting that olfactory signals played a more significant role in the compound bimodal condition. This was supported by the fact that after 24 h, most bimodal-treatment bees responded to odour but not visual stimuli. We did not observe differences in latency of response, suggesting that signal composition affected decision accuracy, not speed. We conclude that restrained bumble bee workers exhibit broad variation of responses to bimodal stimuli and that components of the bimodal signal may not be used equivalently. The analysis of bee performance under restrained conditions enables accurate control of the multimodal stimuli provided to individuals and to study the interaction of individual components within a compound.
• Gronenberg, W., & Godfrey, R. K. (2019). Brain evolution in social insects: advocating for the comparative approach.. Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology, 205(1), 13-32. doi:10.1007/s00359-019-01315-7
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  Sociality is classified as one of the major transitions in the evolution of complexity and much effort has been dedicated to understanding what traits predispose lineages to sociality. Conversely, studies addressing the role of sociality in brain evolution (e.g., the social brain hypothesis) have not focused on particular traits and instead relied largely on measurements of relative brain composition. Hymenoptera range from solitary to advanced social species, providing enticing comparisons for studying sociality and neural trait evolution. Here we argue that measuring the role of sociality in brain evolution will benefit from attending to recent advances in neuroethology and adopting existing phylogenetic comparative methods employed in analysis of non-neural traits. Such analyses should rely on traits we expect to vary at the taxonomic level used in comparative analyses and include phylogenetic structure. We outline the limits of brain size and volumetric interpretation and advocate closer attention to trait stability and plasticity at different levels of organization. We propose neural traits measured at the cellular, circuit, and molecular levels will serve as more robust variables for evolutionary analyses. We include examples of particular traits and specific clades that are well-suited to answer questions about the role of sociality in nervous system evolution.
• Gronenberg, W., & Gowda, V. (2019). Brain composition and scaling in social bee species differing in body size. Apidologie, 50(6), 779-792. doi:10.1007/s13592-019-00685-w
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  We compare four honeybee and one bumblebee species with similar behaviors and ecological requirements but large differences in body size. The bees show allometric brain-body size relationships and scaling exponents similar to those found in vertebrates. Compared with three Asian honeybee species, the European honeybee Apis mellifera feature larger brains than expected for their body mass. Overall, the brains show moderate regional variation across species with two pronounced differences: A. dorsata have an enlarged visual lamina, possibly an adaptation for crepuscular vision. Second, the mushroom bodies are larger and comprise more intrinsic neurons in bumblebees than in honeybees. While these findings might suggest more advanced sensory associations in bumblebees, it is currently not possible to test this notion in the absence of quantitative and comprehensive behavioral comparisons across bee species.
• Leitner, N., Leitner, N. E., Gronenberg, W., Dornhaus, A., & Charbonneau, D. (2019). Peripheral sensory organs vary among ant workers but variation does not predict division of labor.. Behavioural processes, 158, 137-143. doi:10.1016/j.beproc.2018.10.016
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  The neural mechanisms underlying behavioral variation among individuals are not well understood. Differences among individuals in sensory sensitivity could limit the environmental stimuli to which an individual is capable of responding and have, indeed, been shown to relate to behavioral differences in different species. Here, we show that ant workers in Temnothorax rugatulus differ considerably in the number of antennal sensory structures, or sensilla (by 45% in density and over 100% in estimated total number). A larger quantity of sensilla may reflect a larger quantity of underlying sensory neurons. This would increase the probability that a given set of neurons in the antenna detects an environmental stimulus and becomes excited, thereby eliciting the expression of a behavior downstream at lower stimulus levels than an individual with comparatively fewer sensilla. Individual differences in antennal sensilla density, however, did not predict worker activity level or performance of any task, suggesting either that variation in sensilla density does not, in fact, reflect variation in sensory sensitivity or that individual sensory response thresholds to task-associated stimuli do not determine task allocation as is commonly assumed, at least in this social insect. More broadly, our finding that even closely related individuals can differ strongly in peripheral sensory organ elaboration suggests that such variation in sensory organs could underlie other cases of intraspecific behavioral variation.
• Larabee, F. J., Gronenberg, W., & Suarez, A. V. (2017). Performance, morphology and control of power-amplified mandibles in the trap-jaw ant(Hymenoptera: Formicidae). The Journal of experimental biology, 220(Pt 17), 3062-3071.
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  Trap-jaw ants are characterized by high-speed mandibles used for prey capture and defense. Power-amplified mandibles have independently evolved at least four times among ants, with each lineage using different structures as a latch, spring and trigger. We examined two species from the genus(subfamily Formicinae), whose morphology is unique among trap-jaw ant lineages, and describe the performance characteristics, spring-loading mechanism and neuronal control ofstrikes. Like other trap-jaw ants,latch their jaws open while the large closer muscle loads potential energy in a spring. The latch differs from other lineages and is likely formed by the co-contraction of the mandible opener and closer muscles. The cuticle of the posterior margin of the head serves as a spring, and is deformed by approximately 6% prior to a strike. The mandibles are likely unlatched by a subgroup of closer muscle fibers with particularly short sarcomeres. These fast fibers are controlled by two large motor neurons whose dendrites overlap with terminals of large sensory neurons originating from labral trigger hairs. Upon stimulation of the trigger hairs, the mandibles shut in as little as 0.5 ms and at peak velocities that are comparable with other trap-jaw ants, but with much slower acceleration. The estimated power output of the mandible strike (21 kW kg) confirms thatjaws are indeed power amplified. However, the power output ofmandibles is significantly lower than distantly related trap-jaw ants using different spring-loading mechanisms, indicating a relationship between power-amplification mechanism and performance.
• Gronenberg, W., Wiegmann, D., Hebets, E., & Bingman, V. (2016). Amblypygids: Model Organisms for the Study of Arthropod Navigation Mechanisms in Complex Environments?. Frontiers in Behavioral Neuroscience, 10, 8. doi:10.3389/fnbeh.2016.00047
• Kamhi, J. F., Gronenberg, W., Robson, S., & Traniello, J. (2016). Social complexity influences brain investment and neural operation costs in ants. PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES, 283(1841).
• Wcislo, W. T., Mueller, U. G., Gronenberg, W., & Amador-vargas, S. (2015). Specialization and group size: brain and behavioural correlates of colony size in ants lacking morphological castes.. Proceedings. Biological sciences, 282(1801), 20142502. doi:10.1098/rspb.2014.2502
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  Group size in both multicellular organisms and animal societies can correlate with the degree of division of labour. For ants, the task specialization hypothesis (TSH) proposes that increased behavioural specialization enabled by larger group size corresponds to anatomical specialization of worker brains. Alternatively, the social brain hypothesis proposes that increased levels of social stimuli in larger colonies lead to enlarged brain regions in all workers, regardless of their task specialization. We tested these hypotheses in acacia ants (Pseudomyrmex spinicola), which exhibit behavioural but not morphological task specialization. In wild colonies, we marked, followed and tested ant workers involved in foraging tasks on the leaves (leaf-ants) and in defensive tasks on the host tree trunk (trunk-ants). Task specialization increased with colony size, especially in defensive tasks. The relationship between colony size and brain region volume was task-dependent, supporting the TSH. Specifically, as colony size increased, the relative size of regions within the mushroom bodies of the brain decreased in trunk-ants but increased in leaf-ants; those regions play important roles in learning and memory. Our findings suggest that workers specialized in defence may have reduced learning abilities relative to leaf-ants; these inferences remain to be tested. In societies with monomorphic workers, brain polymorphism enhanced by group size could be a mechanism by which division of labour is achieved.
• Amador-Vargas, S., Gronenberg, W., Wcislo, W., & Mueller, U. (2014). Specialization and group size: brain and behavioral correlates of colony size in ants lacking morphological castes. Proc R Soc B DOI: 10.1098/rspb.2014.2502.
• Fischer, N., Gronenberg, W., & Dornhaus, A. R. (2014). Investigating neural mechanisms underlying division of labor in Temnothorax ants.. 17th Congress of the International Union for the Study of Social Insects (IUSSI), Cairns, Australia,.
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  33 - Behavioural ecology and neurobiology of cognition in social insects, Oral Presentation
• Gronenberg, W., Raikhellkar, A., Abshire, E., Stevens, J., Epstein, E., Loyola, K., Rauscher, M., & Buchmann, S. (2014). Honey bees (Apis mellifera) learn to discriminate the smell of organic compounds from their respective deuterated isotopomers. Proc. R. Soc. B.
• Muscedere, M., Gronenberg, W., Moreau, C., & Traniello, J. (2014). Investment in higher-order central processing regions is not constrained by brain size in social insects. Proc. R. Soc. B, 281.
• Terrapon, N., Li, C., Robertson, H. M., Ji, L., Meng, X., Booth, W., Chen, Z., Childers, C. P., Glastad, K. M., Gokhale, K., Gowin, J., Gronenberg, W., Hermansen, R. A., Hu, H., Hunt, B. G., Huylmans, A. K., Khalil, S. M., Mitchell, R. D., Munoz-Torres, M. C., , Mustard, J. A., et al. (2014). Molecular traces of alternative social organization in a termite genome. Nature communications, 5, 3636.
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  Although eusociality evolved independently within several orders of insects, research into the molecular underpinnings of the transition towards social complexity has been confined primarily to Hymenoptera (for example, ants and bees). Here we sequence the genome and stage-specific transcriptomes of the dampwood termite Zootermopsis nevadensis (Blattodea) and compare them with similar data for eusocial Hymenoptera, to better identify commonalities and differences in achieving this significant transition. We show an expansion of genes related to male fertility, with upregulated gene expression in male reproductive individuals reflecting the profound differences in mating biology relative to the Hymenoptera. For several chemoreceptor families, we show divergent numbers of genes, which may correspond to the more claustral lifestyle of these termites. We also show similarities in the number and expression of genes related to caste determination mechanisms. Finally, patterns of DNA methylation and alternative splicing support a hypothesized epigenetic regulation of caste differentiation.
• Giraldo, Y. M., Patel, E., Gronenberg, W., & Traniello, J. F. (2013). Division of labor and structural plasticity in an extrinsic serotonergic mushroom body neuron in the ant Pheidole dentata. Neuroscience Letters, 534(1), 107-111.
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  PMID: 23274482;Abstract: Worker polyphenisms in ants enable insightful analyses of neuronal underpinnings of division of labor, a crucial aspect of animal social organization. In the ant Pheidole dentata, which has a dimorphic worker caste, serotonin titer increases in the brain with age, modulating pheromonal recruitment communication and foraging, behaviors characteristic of mature individuals. Serotonin-immunoreactive (5HT-IR) neurons are found in the mushroom bodies (MB) and may modulate multi-sensory information processing associated with cues and social signals guiding task performance. The volume of this neuropil correlates with worker subcaste and age in P. dentata, but the role of structural variation in individual extrinsic MB neurons in division of labor in ants is poorly understood. We tested the hypothesis that branching complexity in a 5HT-IR calyx input neuron (CIN) in the MBs increases with age in minor workers of P. dentata in association with task repertoire expansion. We further predicted that major workers, which are defense specialists, have less elaborate CIN axonal arbors at any age in comparison to minor workers, which are task generalists. Contrary to our predictions, immunohistochemical and morphometric analyses revealed significantly greater CIN branching in both newly eclosed and mature major workers, and identified an effect of worker age on branching complexity only in majors. Our results indicate a modulatory role of the CIN in subcaste-specific behaviors and suggest behavioral specialization may be associated with the elaboration of specific MB neurons. © 2012 Elsevier Ireland Ltd.
• Jones, B. M., Leonard, A. S., Papaj, D. R., & Gronenberg, W. (2013). Plasticity of the worker bumblebee brain in relation to age and rearing environment. BRAIN, BEHAVIOR AND EVOLUTION, 82, 250-261. doi:doi: 10.1159/000355845
• Jones, M., Leonard, A., papaj, D., & Gronenberg, W. (2013). Plasticity of the worker bumblebee brain in relation to age and rearing environment. Brain Behav. Evol..
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  DOI: 10.1159/000355845
• Mota, T., Gronenberg, W., Giurfa, M., & Sandoz, J. (2013). Chromatic processing in the anterior optic tubercle of the honey bee brain. Journal of Neuroscience, 33(1), 4-16.
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  PMID: 23283317;Abstract: Color vision in honey bees (Apis mellifera) has been extensively studied at the behavioral level and, to a lesser degree, at the physiological level by means of electrophysiological intracellular recordings of single neurons. Few visual neurons have been so far characterized in the lateral protocerebrum of bees. Therefore, the possible implication of this region in chromatic processing remains unknown. We performed in vivo calcium imaging of interneurons in the anterior optic tubercle (AOTu) of honey bees upon visual stimulation of the compound eye to analyze chromatic response properties. Stimulation with distinct monochromatic lights (ultraviolet [UV], blue, and green) matching the sensitivity of the three photoreceptor types of the bee retina induced different signal amplitudes, temporal dynamics, and spatial activity patterns in the AOTu intertubercle network, thus revealing intricate chromatic processing properties. Green light strongly activated both the dorsal and ventral lobes of the AOTu's major unit; blue light activated the dorsal lobe more while UV light activated the ventral lobe more. Eye stimulation with mixtures of blue and green light induced suppression phenomena in which responses to the mixture were lower than those to the color components, thus concurring with color-opponent processing. These data provide evidence for a spatial segregation of color processing in the AOTu, which may serve for navigation purposes. © 2013 the authors.
• Riveros, A. J., & Gronenberg, W. -. (2012). Decision-making and associative color learning in harnessed bumblebees (Bombus impatiens). Animal cognition, 15(6).
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  In honeybees, the conditioning of the proboscis extension response (PER) has provided a powerful tool to explore the mechanisms underlying olfactory learning and memory. Unfortunately, PER conditioning does not work well for visual stimuli in intact honeybees, and performance is improved only after antennal amputation, thus limiting the analysis of visual learning and multimodal integration. Here, we study visual learning using the PER protocol in harnessed bumblebees, which exhibit high levels of odor learning under restrained conditions. We trained bumblebees in a differential task in which two colors differed in their rewarding values. We recorded learning performance as well as response latency and accuracy. Bumblebees rapidly learned the task and discriminated the colors within the first two trials. However, performance varied between combinations of colors and was higher when blue or violet was associated with a high reward. Overall, accuracy and speed were negatively associated, but both components increased during acquisition. We conclude that PER conditioning is a good tool to study visual learning, using Bombus impatiens as a model, opening new possibilities to analyze the proximate mechanisms of visual learning and memory, as well as the process of multimodal integration and decision-making.
• Mota, T., Yamagata, N., Giurfa, M., Gronenberg, W., & Sandoz, J. (2011). Neural organization and visual processing in the anterior optic tubercle of the honeybee brain. Journal of Neuroscience, 31(32), 11443-11456.
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  PMID: 21832175;Abstract: The honeybee Apis mellifera represents a valuable model for studying the neural segregation and integration of visual information. Vision in honeybees has been extensively studied at the behavioral level and, to a lesser degree, at the physiological level using intracellular electrophysiological recordings of single neurons. However, our knowledge of visual processing in honeybees is still limited by the lack of functional studies of visual processing at the circuit level. Here we contribute to filling this gap by providing a neuroanatomical and neurophysiological characterization at the circuit level of a practically unstudied visual area of the bee brain, the anterior optic tubercle (AOTu). First, we analyzed the internal organization and neuronal connections of the AOTu. Second, we established a novel protocol for performing optophysiological recordings of visual circuit activity in the honeybee brain and studied the responses of AOTu interneurons during stimulation of distinct eye regions. Our neuroanatomical data show an intricate compartmentalization and connectivity of the AOTu, revealing a dorsoventral segregation of the visual input to the AOTu. Light stimuli presented in different parts of the visual field (dorsal, lateral, or ventral) induce distinct patterns of activation in AOTu output interneurons, retaining to some extent the dorsoventral input segregation revealed by our neuroanatomical data. In particular, activity patterns evoked by dorsal and ventral eye stimulation are clearly segregated into distinct AOTu subunits. Our results therefore suggest an involvement of the AOTu in the processing of dorsoventrally segregated visual information in the honeybee brain. © 2011 the authors.
• Muscedere, M. L., Traniello, J. F., & Gronenberg, W. (2011). Coming of age in an ant colony: Cephalic muscle maturation accompanies behavioral development in Pheidole dentata. Naturwissenschaften, 98(9), 783-793.
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  PMID: 21792597;Abstract: Although several neurobiological and genetic correlates of aging and behavioral development have been identified in social insect workers, little is known about how other age-related physiological processes, such as muscle maturation, contribute to task performance. We examined post-eclosion growth of three major muscles of the head capsule in major and minor workers of the ant Pheidole dentata using workers of different ages with distinct task repertoires. Mandible closer muscle fibers, which provide bite force and are thus critical for the use of the mandibles for biting and load carrying, fill the posteriolateral portions of the head capsule in mature, older workers of both subcastes. Mandible closer fibers of newly eclosed workers, in contrast, are significantly thinner in both subcastes and grow during at least the next 6 days in minor workers, suggesting this muscle has reduced functionality for a substantial period of adult life and thus constrains task performance capability. Fibers of the antennal muscles and the pharynx dilator, which control antennal movements and food intake, respectively, also increase significantly in thickness with age. However, these fibers are only slightly thinner in newly eclosed workers and attain their maximum thickness over a shorter time span in minors. The different growth rates of these functionally distinct muscles likely have consequences for how adult P. dentata workers, particularly minors, develop their full and diverse task repertoire as they age. Workers may be capable of feeding and interacting socially soon after eclosion, but require a longer period of development to effectively use their mandibles, which enable the efficient performance of tasks ranging from nursing to foraging and defense. © Springer-Verlag 2011.
• Smith, C. R., Smith, C. D., Robertson, H. M., Helmkampf, M., Zimin, A., Yandell, M., Holt, C., Hao, H. u., Abouheif, E., Benton, R., Cash, E., Croset, V., Currie, C. R., Elhaik, E., Elsik, C. G., Favé, M., Fernandes, V., Gibson, J. D., Graur, D., , Gronenberg, W., et al. (2011). Draft genome of the red harvester ant Pogonomyrmex barbatus. Proceedings of the National Academy of Sciences of the United States of America, 108(14), 5667-5672.
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  PMID: 21282651;PMCID: PMC3078412;Abstract: We report the draft genome sequence of the red harvester ant, Pogonomyrmex barbatus. The genome was sequenced using 454 pyrosequencing, and the current assembly and annotation were completed in less than 1 y. Analyses of conserved gene groups (more than 1,200 manually annotated genes to date) suggest a high-quality assembly and annotation comparable to recently sequenced insect genomes using Sanger sequencing. The red harvester ant is a model for studying reproductive division of labor, phenotypic plasticity, and sociogenomics. Although the genome of P. barbatus is similar to other sequenced hymenopterans (Apis mellifera and Nasonia vitripennis) in GC content and compositional organization, and possesses a complete CpG methylation toolkit, its predicted genomic CpG content differs markedly from the other hymenopterans. Gene networks involved in generating key differences betweenthe queenandworker castes (e.g.,wingsandovaries) showsignatures of increasedmethylation and suggest that ants and bees may have independently co-opted the same gene regulatory mechanisms for reproductive division of labor. Gene family expansions (e.g., 344 functional odorant receptors) and pseudogene accumulation in chemoreception and P450 genes compared with A. mellifera and N. vitripennis are consistent with major life-history changes during the adaptive radiation of Pogonomyrmex spp., perhaps inparallel with the development of the North American deserts.
• Couvillon, M. J., Degrandi-Hoffman, G., & Gronenberg, W. (2010). Africanized honeybees are slower learners than their European counterparts. Naturwissenschaften, 97(2), 153-160.
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  PMID: 19904521;Abstract: Does cognitive ability always correlate with a positive fitness consequence? Previous research in both vertebrates and invertebrates provides mixed results. Here, we compare the learning and memory abilities of Africanized honeybees (Apis mellifera scutellata hybrid) and European honeybees (Apis mellifera ligustica). The range of the Africanized honeybee continues to expand, superseding the European honeybee, which led us to hypothesize that they might possess greater cognitive capabilities as revealed by a classical conditioning assay. Surprisingly, we found that fewer Africanized honeybees learn to associate an odor with a reward. Additionally, fewer Africanized honeybees remembered the association a day later. While Africanized honeybees are replacing European honeybees, our results show that they do so despite displaying a relatively poorer performance on an associative learning paradigm. © 2009 Springer-Verlag.
• Gronenberg, W., & Couvillon, M. J. (2010). Brain composition and olfactory learning in honey bees. Neurobiology of Learning and Memory, 93(3), 435-443.
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  PMID: 20060918;Abstract: Correlations between brain or brain component size and behavioral measures are frequently studied by comparing different animal species, which sometimes introduces variables that complicate interpretation in terms of brain function. Here, we have analyzed the brain composition of honey bees (Apis mellifera) that have been individually tested in an olfactory learning paradigm. We found that the total brain size correlated with the bees' learning performance. Among different brain components, only the mushroom body, a structure known to be involved in learning and memory, showed a positive correlation with learning performance. In contrast, visual neuropils were relatively smaller in bees that performed better in the olfactory learning task, suggesting modality-specific behavioral specialization of individual bees. This idea is also supported by inter-individual differences in brain composition. Some slight yet statistically significant differences in the brain composition of European and Africanized honey bees are reported. Larger bees had larger brains, and by comparing brains of different sizes, we report isometric correlations for all brain components except for a small structure, the central body. © 2010 Elsevier Inc.
• Riveros, A. J., & Gronenberg, W. (2010). Brain allometry and neural plasticity in the bumblebee bombus occidentalis. Brain, Behavior and Evolution, 75(2), 138-148.
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  PMID: 20516659;PMCID: PMC2914411;Abstract: Brain plasticity is a common phenomenon across animals and in many cases it is associated with behavioral transitions. In social insects, such as bees, wasps and ants, plasticity in a particular brain compartment involved in multisensory integration (the mushroom body) has been associated with transitions between tasks differing in cognitive demands. However, in most of these cases, transitions between tasks are age-related, requiring the experimental manipulation of the age structure in the studied colonies to distinguish age and experience-dependent effects. To better understand the interplay between brain plasticity and behavioral performance it would therefore be advantageous to study species whose division of labor is not age-dependent. Here, we focus on brain plasticity in the bumblebee Bombus occidentalis, in which division of labor is strongly affected by the individual's body size instead of age. We show that, like in vertebrates, body size strongly correlates with brain size. We also show that foraging experience, but not age, significantly correlates with the increase in the size of the mushroom body, and in particular one of its components, the medial calyx. Our results support previous findings from other social insects suggesting that the mushroom body plays a key role in experience-based decision making. We also discuss the use of bumblebees as models to analyze neural plasticity and the association between brain size and behavioral performance. Copyright © 2010 S. Karger AG, Basel.
• Riveros, A. J., & Gronenberg, W. (2010). Sensory allometry, foraging task specialization and resource exploitation in honeybees. Behavioral Ecology and Sociobiology, 64(6), 955-966.
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  Abstract: Insect societies are important models for evolutionary biology and sociobiology. The complexity of some eusocial insect societies appears to arise from self-organized task allocation and group cohesion. One of the best-supported models explaining self-organized task allocation in social insects is the response threshold model, which predicts specialization due to inter-individual variability in sensitivity to task-associated stimuli. The model explains foraging task specialization among honeybee workers, but the factors underlying the differences in individual sensitivity remain elusive. Here, we propose that in honeybees, sensory sensitivity correlates with individual differences in the number of sensory structures, as it does in solitary species. Examining European and Africanized honeybees, we introduce and test the hypothesis that body size and/or sensory allometry is associated with foraging task preferences and resource exploitation. We focus on common morphological measures and on the size and number of structures associated with olfactory sensitivity. We show that the number of olfactory sensilla is greater in pollen and water foragers, which are known to exhibit higher sensory sensitivity, compared to nectar foragers. These differences are independent of the distribution of size within a colony. Our data also suggest that body mass and number of olfactory sensilla correlate with the concentration of nectar gathered by workers, and with the size of pollen loads they carry. We conclude that sensory allometry, but not necessarily body size, is associated with resource exploitation in honeybees and that the differences in number of sensilla may underlie the observed differences in sensitivity between bees specialized on water, pollen and nectar collection. © 2010 Springer-Verlag.
• Gronenberg, W., Snell-Rood, E. C., Papaj, D. R., & Gronenberg, W. -. (2009). Brain size: a global or induced cost of learning?. Brain, behavior and evolution, 73(2).
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  The role of brain size as a cost of learning remains enigmatic; the nature and timing of such costs is particularly uncertain. On one hand, comparative studies suggest that congenitally large brains promote better learning and memory. In that case, brain size exacts a global cost that accrues even if learning does not take place; on the other hand, some developmental studies suggest that brains grow with experience, indicating a cost that is induced when learning occurs. The issue of how costs are incurred is an important one, because global costs are expected to constrain the evolution of learning more than would induced costs. We tested whether brain size represented a global and/or an induced cost of learning in the cabbage white butterfly, Pieris rapae. We assayed the ability of full sibling families to learn to locate either green hosts, for which butterflies have an innate search bias, or red hosts, which are more difficult to learn to locate. Naïve butterflies were sacrificed at emergence and congenital brain volume estimated as a measure of global costs; experienced butterflies were sacrificed after learning and change in brain volume estimated as a measure of induced costs. Only for the mushroom body, a brain region involved in learning and memory in other insects, was volume at emergence related to learning or host-finding. Butterfly families that emerged with relatively larger mushroom bodies showed a greater tendency to improve their ability to find red hosts across the two days of host-search. The volume of most brain regions increased with time in a manner suggesting host experience itself was important: first, total number of landings during host-search was positively related to mushroom body calyx volume, and, second, experience with the red host was positively related to mushroom body lobe volume. At the family level, the relative volume of the mushroom body calyx and antennal lobes following learning was positively related to overall success in finding red hosts. Overall, our results suggest that within species, brain size might act as a small global cost of learning, but that environment-specific changes in brain size might reduce the overall costs of neural tissue in the evolution of learning.
• Paulk, A. C., Dacks, A. M., & Gronenberg, W. (2009). Color processing in the medulla of the bumblebee (Apidae: Bombus impatiens). Journal of Comparative Neurology, 513(5), 441-456.
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  PMID: 19226517;Abstract: The mechanisms of processing a visual scene involve segregating features (such as color) into separate information channels at different stages within the brain, processing these features, and then integrating this information at higher levels in the brain. To examine how this process takes place in the insect brain, we focused on the medulla, an area within the optic lobe through which all of the visual information from the retina must pass before it proceeds to central brain areas. We used histological and immunocytochemical techniques to examine the bumblebee medulla and found that the medulla is divided into eight layers. We then recorded and morphologically identified 27 neurons with processes in the medulla. During our recordings we presented color cues to determine whether response types correlated with locations of the neural branching patterns of the filled neurons among the medulla layers. Neurons in the outer medulla layers had less complex color responses compared to neurons in the inner medulla layers and there were differences in the temporal dynamics of the responses among the layers. Progressing from the outer to the inner medulla, neurons in the different layers appear to process increasingly complex aspects of the natural visual scene. © 2009 Wiley-Liss, Inc.
• Paulk, A. C., Dacks, A. M., Phillips-Portillo, J., Fellous, J., & Gronenberg, W. (2009). Visual processing in the central bee brain. Journal of Neuroscience, 29(32), 9987-9999.
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  PMID: 19675233;PMCID: PMC2746979;Abstract: Visual scenes comprise enormous amounts of information from which nervous systems extract behaviorally relevant cues. In most model systems, little is known about the transformation of visual information as it occurs along visual pathways. We examined how visual information is transformed physiologically as it is communicated from the eye to higher-order brain centers using bumblebees, which are known for their visual capabilities. We recorded intracellularly in vivo from 30 neurons in the central bumblebee brain (the lateral protocerebrum) and compared these neurons to 132 neurons from more distal areas along the visual pathway, namely the medulla and the lobula. In these three brain regions (medulla, lobula, and central brain), we examined correlations between the neurons' branching patterns and their responses primarily to color, but also to motion stimuli. Visual neurons projecting to the anterior central brain were generally color sensitive, while neurons projecting to the posterior central brain were predominantly motion sensitive. The temporal response properties differed significantly between these areas, with an increase in spike time precision across trials and a decrease in average reliable spiking as visual information processing progressed from the periphery to the central brain. These data suggest that neurons along the visual pathway to the central brain not only are segregated with regard to the physical features of the stimuli (e.g., color and motion), but also differ in the way they encode stimuli, possibly to allow for efficient parallel processing to occur. Copyright © 2009 Society for Neuroscience.
• Riveros, A. J., & Gronenberg, W. (2009). Learning from learning and memory in bumblebees. Communicative and Integrative Biology, 2(5), 437-440.
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  PMID: 19907712;PMCID: PMC2775245;Abstract: The difficulty to simultaneously record neural activity and behavior presents a considerable limitation for studying mechanisms of insect learning and memory. The challenge is finding a model suitable for the use of behavioral paradigms under the restrained conditions necessary for neural recording. In honey-bees, Pavlovian conditioning relying on the proboscis extension reflex (PER) has been used with great success to study different aspects of insect cognition. However, it is desirable to combine the advantages of the PER with a more robust model that allows simultaneous electrical or optical recording of neural activity. Here, we briefly discuss the potential use of bumblebees as models for the study of learning and memory under restrained conditions. We base our arguments on the well-known cognitive abilities of bumblebees, their social organization and phylogenetic proximity to honeybees, our recent success using Pavlovian conditioning to study learning in two bumblebee species, and on the recently demonstrated robustness of bumblebees under conditions suitable for electrophysiological recording. © 2009 Landes Bioscience.
• Riveros, A. J., & Gronenberg, W. (2009). Olfactory learning and memory in the bumblebee Bombus occidentalis. Naturwissenschaften, 96(7), 851-856.
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  PMID: 19322551;Abstract: In many respects, the behavior of bumblebees is similar to that of the closely related honeybees, a long-standing model system for learning and memory research. Living in smaller and less regulated colonies, bumblebees are physiologically more robust and thus have advantages in particular for indoor experiments. Here, we report results on Pavlovian odor conditioning of bumblebees using the proboscis extension reflex (PER) that has been successfully used in honeybee learning research. We examine the effect of age, body size, and experience on learning and memory performance. We find that age does not affect learning and memory ability, while body size positively correlates with memory performance. Foraging experience seems not to be necessary for learning to occur, but it may contribute to learning performance as bumblebees with more foraging experience on average were better learners. The PER represents a reliable tool for learning and memory research in bumblebees and allows examining interspecific similarities and differences of honeybee and bumblebee behavior, which we discuss in the context of social organization. © 2009 Springer-Verlag.
• DeGrandi-Hoffman, G., Lucas, T., Gronenberg, W., & Caseman, D. (2008). Brains and brain components in African and European honey bees (Hymenoptera: Apidae) - A volumetric comparison. Journal of Apicultural Research, 47(4), 281-285.
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  Abstract: The volumes of brains and major brain regions were compared between European (EHB) and African (AHB) honey bee workers. The brain volume was not significantly different between the two bee races. The overall composition of major brain regions appeared similar except for the lobes of the mushroom bodies, which were significantly larger in EHB. Discriminant analysis indicated that brains from EHB could be distinguished from those of AHB based on the volumes of the central body together with either the mushroom body lobe or the mushroom body calyx. Whether learning and memory capacities differ between AHB and EHB based on the size of mushroom body lobes and whether the differences are adaptive due to the environments where EHB and AHB originated are discussed. © IBRA 2008.
• Paulk, A. C., & Gronenberg, W. (2008). Higher order visual input to the mushroom bodies in the bee, Bombus impatiens. Arthropod Structure and Development, 37(6), 443-458.
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  PMID: 18635397;PMCID: PMC2571118;Abstract: To produce appropriate behaviors based on biologically relevant associations, sensory pathways conveying different modalities are integrated by higher-order central brain structures, such as insect mushroom bodies. To address this function of sensory integration, we characterized the structure and response of optic lobe (OL) neurons projecting to the calyces of the mushroom bodies in bees. Bees are well known for their visual learning and memory capabilities and their brains possess major direct visual input from the optic lobes to the mushroom bodies. To functionally characterize these visual inputs to the mushroom bodies, we recorded intracellularly from neurons in bumblebees (Apidae: Bombus impatiens) and a single neuron in a honeybee (Apidae: Apis mellifera) while presenting color and motion stimuli. All of the mushroom body input neurons were color sensitive while a subset was motion sensitive. Additionally, most of the mushroom body input neurons would respond to the first, but not to subsequent, presentations of repeated stimuli. In general, the medulla or lobula neurons projecting to the calyx signaled specific chromatic, temporal, and motion features of the visual world to the mushroom bodies, which included sensory information required for the biologically relevant associations bees form during foraging tasks. © 2008 Elsevier Ltd. All rights reserved.
• Paulk, A. C., Phillips-Portillo, J., Dacks, A. M., Fellous, J., & Gronenberg, W. (2008). The processing of color, motion, and stimulus timing are anatomically segregated in the bumblebee brain. Journal of Neuroscience, 28(25), 6319-6332.
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  PMID: 18562602;PMCID: PMC3844780;Abstract: Animals use vision to perform such diverse behaviors as finding food, interacting socially with other animals, choosing a mate, and avoiding predators. These behaviors are complex and the visual system must process color, motion, and pattern cues efficiently so that animals can respond to relevant stimuli. The visual system achieves this by dividing visual information into separate pathways, but to what extent are these parallel streams separated in the brain? To answer this question, we recorded intracellularly in vivo from 105 morphologically identified neurons in the lobula, a major visual processing structure of bumblebees (Bombus impatiens). We found that these cells have anatomically segregated dendritic inputs confined to one or two of six lobula layers. Lobula neurons exhibit physiological characteristics common to their respective input layer. Cells with arborizations in layers 1-4 are generally indifferent to color but sensitive to motion, whereas layer 5-6 neurons often respond to both color and motion cues. Furthermore, the temporal characteristics of these responses differ systematically with dendritic branching pattern. Some layers are more temporally precise, whereas others are less precise but more reliable across trials. Because different layers send projections to different regions of the central brain, we hypothesize that the anatomical layers of the lobula are the structural basis for the segregation of visual information into color, motion, and stimulus timing. Copyright © 2008 Society for Neuroscience.
• Schmitz, H., Schmitz, A., Kreiss, E., Gebhardt, M., & Gronenberg, W. (2008). Navigation to forest fires by smoke and infrared reception: The specialized sensory systems of "fire-loving" beetles. Navigation, Journal of the Institute of Navigation, 55(2), 137-145.
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  Abstract: "Fire-loving" (pyrophilous) beetles depend on forest fires for their reproduction. Such insects approach ongoing fires and invade the burnt area immediately. Two genera of pyrophilous jewel beetles (Buprestidae) and one species of the genus Acanthocnemus (Acanthocnemidae) show a highly pyrophilous behavior. For the long-range navigation towards a fire as well as for the short-range orientation on a freshly burnt area these beetles have special sensors for smoke and infrared (IR) radiation. In the best studied beetle, Melanophila acuminata, infrared receptors and their associated sensory neurons are derived from mechanoreceptors. Unlike other mechanosensory neurons, IR sensitive neurons directly send their information to be processed centrally (e.g., by the brain) rather than locally in their respective ganglia of origin. It is suggested that smoke-derived odors and IR information converge on descending brain neurons which, in turn, control and direct flight toward the forest fire.
• Tibbetts, E. A., Gronenberg, W., & Ash, L. E. (2008). Correlation between facial pattern recognition and brain composition in paper wasps.. Brain, behavior and evolution, 71(1), 1-14. doi:10.1159/000108607
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  Unique among insects, some paper wasp species recognize conspecific facial patterns during social communication. To evaluate whether specialized brain structures are involved in this task, we measured brain and brain component size in four different paper wasp species, two of which show facial pattern recognition. These behavioral abilities were not reflected by an increase in brain size or an increase in the size of the primary visual centers (medulla, lobula). Instead, wasps showing face recognition abilities had smaller olfactory centers (antennal lobes). Although no single brain compartment explains the wasps' specialized visual abilities, multi-factorial analysis of the different brain components, particularly the antennal lobe and the mushroom body sub-compartments, clearly separates those species that show facial pattern recognition from those that do not. Thus, there appears to be some neural specialization for visual communication in Polistes. However, the apparent lack of optic lobe specialization suggests that the visual processing capabilities of paper wasps might be preadapted for pattern discrimination and the ability to discriminate facial markings could require relatively small changes in their neuronal substrate.
• Gronenberg, W., Ash, L. E., & Tibbetts, E. A. (2007). Correlation between facial pattern recognition and brain composition in paper wasps. Brain, Behavior and Evolution, 71(1), 1-14.
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  PMID: 17878714;Abstract: Unique among insects, some paper wasp species recognize conspecific facial patterns during social communication. To evaluate whether specialized brain structures are involved in this task, we measured brain and brain component size in four different paper wasp species, two of which show facial pattern recognition. These behavioral abilities were not reflected by an increase in brain size or an increase in the size of the primary visual centers (medulla, lobula). Instead, wasps showing face recognition abilities had smaller olfactory centers (antennal lobes). Although no single brain compartment explains the wasps' specialized visual abilities, multi-factorial analysis of the different brain components, particularly the antennal lobe and the mushroom body sub-compartments, clearly separates those species that show facial pattern recognition from those that do not. Thus, there appears to be some neural specialization for visual communication in Polistes. However, the apparent lack of optic lobe specialization suggests that the visual processing capabilities of paper wasps might be preadapted for pattern discrimination and the ability to discriminate facial markings could require relatively small changes in their neuronal substrate. Copyright © 2007 S. Karger AG.
• Schmitz, H., Schmitz, A., Kreiss, E., Gebhardt, M., & Gronenberg, W. (2007). Navigation to forest fires by smoke and infrared reception: The specialized sensory systems of "fire-loving" beetles. Proceedings of the Annual Meeting - Institute of Navigation, 121-129.
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  Abstract: "Fire-loving" (pyrophilous) beetles depend on forest fires for their reproduction. Such insects approach ongoing fires and invade the burnt area immediately. Two genera of pyrophilous jewel beetles (Buprestidae) and one species of the genus Acanthocnemus (Acanthocnemidae) show a highly pyrophilous behaviour. For the long-range navigation towards a fire as well as for the short-range orientation on a freshly burnt area these beetles have special sensors for smoke and infrared (IR) radiation. Whereas the olfactory receptors for smoke are located on the antennae, the IR receptors are housed in extraantennal sensory organs which can be found on the thorax or on the abdomen. In the best-studied beetle, Melanophila acuminata, infrared receptors and their associated sensory neurons are derived from mechanoreceptors. Unlike other mechanosensory neurons, IR sensitive neurons directly send their information to be processed centrally (e.g. by the brain) rather than locally in their respective ganglia of origin. It is suggested that smoke - derived odours and IR information converge on descending brain neurons which, in turn, control and direct flight toward the forest fire.
• Mares, S., Ash, L., & Gronenberg, W. (2005). Brain allometry in bumblebee and honey bee workers. Brain, Behavior and Evolution, 66(1), 50-61.
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  PMID: 15821348;Abstract: Within a particular animal taxon, larger bodied species generally have larger brains. Increased brain size usually correlates with increased behavioral repertoires and often with superior cognitive abilities. Bumblebees are eusocial insects that show pronounced size polymorphism among workers, whereas in honey bees size variation is much less pronounced. Recent studies suggest that within a given colony, large bumblebee workers are more efficient foragers and are better learners than their smaller sisters. Here we examine the allometric relationship between brain and body size of worker bumblebees and honey bees. We find that larger bees have larger brains and that most brain components show a similar size increase as the overall brain. One particular brain structure, the central body, is relatively smaller in large bumblebees compared to small bees. The same is true for the mushroom body lobes, whereas the mushroom body calyces, which receive sensory input, are not reduced in larger bumblebees or honey bees. Honey bees have relatively smaller brains, as well as smaller mushroom bodies, than bumblebee workers. We discuss why brain or mushroom body size does not necessarily correlate with the degree of a species' social organization. Copyright © 2005 S. Karger AG.
• Ramón, F., & Gronenberg, W. (2005). Electrical potentials indicate stimulus expectancy in the brains of ants and bees. Cellular and Molecular Neurobiology, 25(2), 313-327.
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  PMID: 16047544;Abstract: 1. In vertebrates, and in humans in particular, so-called 'omitted stimulus potentials' can be electrically recorded from the brain or scalp upon repeated stimulation with simple stimuli such as light flashes. 2. While standard evoked potentials follow each stimulus in a series, 'omitted stimulus potentials' occur when an additional stimulus is expected after the end of a stimulus series. These potentials represent neuronal plasticity and are assumed to be involved in basic cognitive processes. 3. We recorded electroretinograms from the eyes and visually evoked potentials from central brain areas of honey bees and ants, social insects to which cognitive abilities have been ascribed and whose rich-behavioral repertoires include navigation, learning and memory. 4. We demonstrate that omitted stimulus potentials occur in these insects. Omitted stimulus potentials in bees and ants show similar temporal characteristics to those found in crayfish and vertebrates, suggesting that common mechanisms may underlie this form of short-term neuronal plasticity. © 2005 Springer Science+Business Media, Inc.
• Ehmer, B., & Gronenberg, W. (2004). Mushroom Body Volumes and Visual Interneurons in Ants: Comparison between Sexes and Castes. Journal of Comparative Neurology, 469(2), 198-213.
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  PMID: 14694534;Abstract: The mushroom bodies are brain centers involved in complex behaviors such as learning and orientation. Here we examine the organization of mushroom bodies in ants, focusing on visual input. We describe the structure of visual neurons and compare the volume of brain structures involved in visual processing, especially the optic lobes and parts of the mushroom bodies receiving visual input in males, winged females, and workers of carpenter ants (Camponotus). A relatively small number of neurons connect the medulla with the mushroom bodies, and these neurons have relatively large dendritic fields in the medulla, suggesting low spatial resolution in ants. These neurons terminate in different yet overlapping strata in the mushroom bodies' collar region. While males have larger optic lobes than workers, their collar region is smaller than in females. Male ants have an additional type of medulla-mushroom body neuron with dendrites probing the distal medulla. These neurons are absent in female and worker ants. Most mushroom body Kenyon cells that are postsynaptic to visual input neurons appear to integrate visual as well as antennal input. This is in contrast to honey bees, where visual input to the mushroom bodies is more prominent and where Kenyon cells are not known to combine visual and antennal input. © 2003 Wiley-Liss, Inc.
• Gronenberg, W., & López-Riquelme, G. (2004). Multisensory convergence in the mushroom bodies of ants and bees. Acta Biologica Hungarica, 55(1-4), 31-37.
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  PMID: 15270216;Abstract: The mushroom bodies, central neuropils in the arthropod brain, are involved in learning and memory and in the control of complex behavior. In most insects, the mushroom bodies receive direct olfactory input in their calyx region. In Hymenoptera, olfactory input is layered in the calyx. In ants, several layers can be discriminated that correspond to different clusters of glomeruli in the antennal lobes, perhaps corresponding to different classes of odors. Only in Hymenoptera, the mushroom body calyx also receives direct visual input from the optic lobes. In bees, six calycal layers receive input from different classes of visual interneurons, probably representing different parts of the visual field and different visual properties. Taken together, the mushroom bodies receive distinct multisensory information in many segregated input layers.
• Gronenberg, W., Doyle, M. P., Yan, M., Hu, W., & Gronenberg, W. -. (2003). Highly selective catalyst-directed pathways to dihydropyrroles from vinyldiazoacetates and imines. Journal of the American Chemical Society, 125(16).
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  Copper-catalyzed reactions of vinyldiazoacetates with imines occur via a pathway in which the activated imine undergoes electrophilic addition to the vinyldiazo compound, whereas reactions catalyzed by rhodium(II) proceed through a metal carbene to an intermediate iminiumylide. Both pathways exhibit high stereoselectivities.
• Ehmer, B., & Gronenberg, W. (2002). Segregation of visual input to the mushroom bodies in the honeybee (Apis mellifera). Journal of Comparative Neurology, 451(4), 362-373.
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  PMID: 12210130;Abstract: Insect mushroom bodies are brain regions that receive multisensory input and are thought to play an important role in learning and memory. In most neopteran insects, the mushroom bodies receive direct olfactory input. In addition, the calyces of Hymenoptera receive substantial direct input from the optic lobes. We describe visual inputs to the calyces of the mushroom bodies of the honeybee Apis mellifera, the neurons'dendritic fields in the optic lobes, the medulla and lobula, and the organization of their terminals in the calyces. Medulla neurons terminate in the collar region of the calyx, where they segregate into five layers that receive alternating input from the dorsal or ventral medulla, respectively. A sixth, innermost layer of the collar receives input from lobula neurons. In the basal ring region of the calyx, medulla neuron terminals are restricted to a small, distal part. Lobula neurons are more prominent in the basal ring, where they terminate in its outer half. Although the collar and basal ring layers generally receive segregated input from both optic neuropils, some overlap occurs at the borders of the layers. At least three different types of mushroom body input neurons originate from the medulla: (a) neurons with narrow dendritic fields mainly restricted to the vicinity of the medulla's serpentine layer and found throughout the medulla; (b) neurons restricted to the ventral half of the medulla and featuring long columnar dendritic branches in the outer medulla; and (c) a group of neurons whose dendrites are restricted to the most ventral part of the medulla and whose axons form the anterior inferior optic tract. Most medulla neurons (groups a and b) send their axons via the anterior superior optic tract to the mushroom bodies. Neurons connecting the lobula with the mushroom bodies have their dendrites in a defined dorsal part of the lobula. Their axons form a third tract to the mushroom bodies, here referred to as the lobula tract. Our findings match the anatomy of intrinsic mushroom body neurons (Strausfeld, 2002) and together indicate that the mushroom bodies may be composed of many more functional subsystems than previously suggested. © 2002 Wiley-Liss, Inc.
• Julian, G. E., & Gronenberg, W. (2002). Reduction of brain volume correlates with behavioral changes in queen ants. Brain, Behavior and Evolution, 60(3), 152-164.
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  PMID: 12417820;Abstract: The behavior of reproductive female ants distinctly changes during the transition from virgin to mature, egg-laying queen. A winged female ant flies only once during her lifetime when she engages in the nuptial flight. Once she is mated she sheds her wings, excavates a nest and starts laying eggs, the basis for her future colony. We show for two species of harvester ants that this transition is accompanied by changes in the performance of behavioral tests: flying virgins are positively phototactic and prefer open areas, whereas young queens prefer the dark, avoid open areas and, given the opportunity, dig into the soil. These behavioral changes coincide with morphological changes in the brain. The brains of mature queens are significantly smaller than those of virgin females at the time of their mating flight. A disproportionately large shrinkage occurs in the medulla and other parts of the visual system during the early adult life of the queen. The brain reduction appears to be adaptive as mature queens show reduced behavioral repertoires and live in the dark. In contrast to virgin females, they do not rely on vision and might increase their fitness by reducing metabolically costly neural tissue. Copyright © 2002 S. Karger AG, Basel.
• Paul, J., & Gronenberg, W. (2002). Motor control of the mandible closer muscle in ants. Journal of Insect Physiology, 48(2), 255-267.
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  Abstract: Despite their simple design, ant mandible movements cover a wide range of forces, velocities and amplitudes. The mandible is controlled by the mandible closer muscle, which is composed of two functionally distinct subpopulations of muscle fiber types: fast fibers (short sarcomeres) and slow ones (long sarcomeres). The entire muscle is controlled by 10-12 motor neurons, 4-5 of which exclusively supply fast muscle fibers. Slow muscle fibers comprise a posterior and an antero-lateral group, each of which is controlled by 1-2 motor neurons. In addition, 3-4 motor neurons control all muscle fibers together. Simultaneous recordings of muscle activity and mandible movement reveal that fast movements require rapid contractions of fast muscle fibers. Slow and subtle movements result from the activation of slow muscle fibers. Forceful movements are generated by simultaneous co-activation of all muscle fiber types. Retrograde tracing shows that most dendritic arborizations of the different sets of motor neurons share the same neuropil in the subesophageal ganglion. In addition, fast motor neurons and neurons supplying the lateral group of slow closer muscle fibers each invade specific parts of the neuropil that is not shared by the other motor neuron groups. Some bilateral overlap between the dendrites of left and right motor neurons exists, particularly in fast motor neurons. The results explain how a single muscle is able to control the different movement parameters required for the proper function of ant mandibles. © 2002 Elsevier Science Ltd. All rights reserved.
• Gronenberg, W. (2001). Subdivisions of hymenopteran mushroom body calyces by their afferent supply. Journal of Comparative Neurology, 435(4), 474-489.
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  PMID: 11406827;Abstract: The mushroom bodies are regions in the insect brain involved in processing complex multimodal information. They are composed of many parallel sets of intrinsic neurons that receive input from and transfer output to extrinsic neurons that connect the mushroom bodies with the surrounding neuropils. Mushroom bodies are particularly large in social Hymenoptera and are thought to be involved in the control of conspicuous orientation, learning, and memory capabilities of these insects. The present account compares the organization of sensory input to the mushroom body's calyx in different Hymenoptera. Tracer and conventional neuronal staining procedures reveal the following anatomic characteristics: The calyx comprises three subdivisions, the lip, collar, and basal ring. The lip receives antennal lobe afferents, and these olfactory input neurons can terminate in two or more segregated zones within the lip. The collar receives visual afferents that are bilateral with equal representation of both eyes in each calyx. Visual inputs provide two to three layers of processes in the collar subdivision. The basal ring is subdivided into two modality-specific zones, one receiving visual, the other antennal lobe input. Some overlap of modality exists between calycal subdivisions and within the basal ring, and the degree of segregation of sensory input within the calyx is species-specific. The data suggest that the many parallel channels of intrinsic neurons may each process different aspects of sensory input information. © 2001 Wiley-Liss, Inc.
• Gronenberg, W. (1999). Ant mushroom bodies reflect living conditions and species specific behavior. Comparative Biochemistry and Physiology A-molecular & Integrative Physiology, 124, S56. doi:10.1016/s1095-6433(99)90222-2
• Gronenberg, W. (1999). Modality-specific segregation of input to ant mushroom bodies. Brain, Behavior and Evolution, 54(2), 85-95.
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  PMID: 10529521;Abstract: The mushroom bodies are central brain neuropils involved in the control of complex behavior. In ants, the mushroom bodies are relatively large compared to those of honey bees, whereas the optic lobes of ants are considerably smaller. The general morphology of ant mushroom bodies is similar to that of honey bees. As in other Hymenoptera, the main input region of the mushroom bodies, the calyx, is subdivided into three compartments: the lip, the collar, and the basal ring. In many ant species this compartmentalization is not obvious and can only be visualized using neuronal tracers. The lip region receives antennal input and is large in all ant species, it appears to be composed of at least two different regions that have not yet been characterized in detail. The collar is large in other Hymenoptera, yet in ant workers it varies in size and is always much smaller than the lip region. The collar receives visual input and is relatively larger in males, which generally are more dependant on vision than are workers. The basal ring receives input from both the optic and antennal lobes. In one ant tribe, the Ponerini, the collar region appears to have changed its position, but based on afferent input it appears to be homologous to the hymenopteran collar. Generally, the composition of the mushroom body calyx correlates with the living conditions of ants, reflecting the great importance of olfaction and the lesser and more variable significance of vision for workers of the observed ant species.
• Gronenberg, W., & Hölldobler, B. (1999). Morphologic representation of visual and antennal information in the ant brain. Journal of Comparative Neurology, 412(2), 229-240.
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  PMID: 10441753;Abstract: Ants in general are primarily olfactory animals, but many species also express visual behaviors. We analyze in 14 species, which range from purely olfactory to predominantly visually behaving ants, how the brains are equipped to control such behavior. We take the size and manifestation of the eyes as an indicator for the prevalence of vision in a given species, and we correlate it with the size of particular brain regions. Our morphometric data show that the size of the eyes generally correlates well with that of the optic lobes. The antennal lobes and the mushroom bodies have a surprisingly constant relative volume whereas, as expected, the relative size of the optic lobes varies strongly across species. Males of different species are more similar. Compared with workers, they all have large eyes, relatively larger optic lobes, smaller mushroom bodies, and similarly sized antennal lobes. The input regions of the mushroom bodies, the lip and the collar, generally correlate with the size of the optic and antennal lobe, respectively. Accordingly, the composition of the calyx reflects the importance of vision for the animal. We present data supporting the view that the mushroom bodies may participate in spatial orientation, landmark recognition, and visual information storage.
• Gronenberg, W., & Liebig, J. (1999). Smaller brains and optic lobes in reproductive workers of the ant Harpegnathos. Naturwissenschaften, 86(7), 343-345.
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  Abstract: Most animals show longterm modifications of their behavior which often reflect an adaptation to seasonal variations (e.g., hibernation) or result from changes in the animal's internal state (e.g., estrous cycle or sexual maturity). Such modifications may substantially affect the nervous system [1, 2]. A particularly striking behavioral change can occur in workers of the ant Harpegnathos. A few young workers in the colony may become reproductives and are thus confined to their dark nest chambers, whereas most workers spend their lives as foragers, employing acute vision when hunting prey. This behavioral difference coincides with a marked decrease in brain volume and with an even stronger reduction in the large visual brain centers. Instead of maintaining superfluous brain functions, these ants reduce brain matter which is expensive to support.
• Gronenberg, W., & Schmitz, H. (1999). Afferent projections of infrared-sensitive sensilla in the beetle Melanophila acuminata (Coleoptera: Buprestidae). Cell and Tissue Research, 297(2), 311-318.
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  PMID: 10470501;Abstract: Beetles of the genus Melanophila are able to detect infrared radiation by using specialized sensilla in their metathoracic pit organs. We describe the afferent projections of the infrared-sensitive neurons in the central nervous system. The axons primarily terminate in the central neuropil of the fused second thoracic ganglia where they establish putative contacts with ascending interneurons. Only a few collaterals appear to be involved in local (uniganglionic) circuits. About half of the neurons send their axons further anterior to the prothoracic ganglion. A subset of these ascend to the subesophageal ganglion, and about 10% project to the brain. Anatomical similarities suggest that the infrared-sensitive neurons are derived from neurons supplying mechanosensory sensilla. The arborization pattern of the infrared afferents suggests that infrared information is processed and integrated upstream from the thoracic ganglia.
• Just, S., & Gronenberg, W. (1999). The control of mandible movements in the ant Odontomachus. Journal of Insect Physiology, 45(3), 231-240.
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  Abstract: Ants use their mandibles to manipulate many different objects including food, brood and nestmates. Different tasks require the modification of mandibular force and speed. Besides normal mandible movements the trap-jaw and Odontomachus features a particularly fast mandible reflex during which both mandibles close synchronously within 3 ms. The mandibular muscles that govern mandible performance are controlled by four opener and eight closer motor neurons. During slow mandible movements different motor units can be activated successively, and fine tuning is assisted by co-activation of the antagonistic muscles. Fast and powerful movements are generated by the additional activation of two particular motor units which also contribute to the mandible strike. The trap-jaw reflex is triggered by a fast trigger muscle which is derived from the mandible closer. Intracellular recording reveals that trigger motor neurons can generate regular as well as particularly large postsynaptic potentials, which might be passively propagated over the short distance to the trigger muscle. The trigger motor neurons are dye-coupled and receive input from both sides of the body without delay, which ensures the synchronous release of both mandibles.
• Paul, J., & Gronenberg, W. (1999). Optimizing force and velocity: Mandible muscle fibre attachments in ants. Journal of Experimental Biology, 202(7), 797-808.
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  Abstract: To be able to perform swift and powerful movements, ant mandible closer muscles are composed of two subpopulations of muscle fibres: fast fibres for rapid actions and slow fibres for forceful biting. All these fibres attach to a sturdy and complex apodeme which conveys force into the mandible base. Fast muscle fibres attach directly to the apodeme. Slow fibres may attach directly or insert at individual thin filament processes of the apodeme which vary in length. Comparisons of different ant species suggest two basic principles underlying the design of mandible muscles. (1) Ants specialized for fast mandible movements generally feature long heads which contain long fast muscle fibres that attach to the apodeme at small angles. Their muscles comprise only a few filament attached fibres and they maximize speed of action at the expense of force output. (2) Ants performing particularly forceful mandible movements, such as seed cracking, rely on many short parallel muscle fibres contained within a broad head capsule. Their slower muscles incorporate a large proportion of filament-attached fibres. Two simple models explain how the attachment angles are optimized with respect to force and velocity output and how filament-attached fibres help to generate the largest power output from the available head capsule volume.
• Gronenberg, W., Hölldobler, B., & Alpert, G. D. (1998). Jaws that snap: Control of mandible movements in the ant Mystrium. Journal of Insect Physiology, 44(3-4), 241-253.
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  Abstract: Ants of the genus Mystrium employ a peculiar snap-jaw mechanism in which the closed mandibles cross over to deliver a stunning blow to an adversary within about 0.5 ms. The mandible snapping is preceded by antennation and antennal withdrawal. The strike is initiated by contact of the adversary with mechanosensory hairs at the side of the mandible, and is powered by large yet slow closer muscles whose energy is stored by a catapult mechanism. Recording of closer muscle activity indicates that the mandibles are not triggered by any fast muscle. Instead, we suppose that activity differences between the left and right mandible muscles imbalance a pivot at the mandible tip and release the strike. The likelihood for the strike to occur can be modulated by an alarm pheromone. The presence of specialized sensilla and for a complex muscle receptor organ shows that the mandibles are also adapted to functions other than snapping and suggests that the force of the mandible can be finely adjusted for other tasks.
• Gronenberg, W., Roberto, C., Brandäo, F., Dietz, B. H., & Just, S. (1998). Trap-jaws revisited: The mandible mechanism of the ant Acanthognathus. Physiological Entomology, 23(3), 227-240.
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  Abstract: Ants of the genus Acanthognathus stalk small insects and catch their prey by a strike with their long, thin mandibles. The mandibles close in less than 2.5 ms and this movement is controlled by a specialized closer muscle. In Acanthognathus, unlike other insects, the mandible closer muscle is subdivided into two distinct parts: as in a catapult, a large slow closer muscle contracts in advance and provides the power for the strike while the mandibles are locked open. When the prey touches specialized trigger hairs, a small fast closer muscle rapidly unlocks the mandibles and thus releases the strike. The fast movement is steadied by large specialized surfaces in the mandible joint and the sensory-motor reflex is controlled by neurones with particularly large, and thus fast-conducting, axons.
• Holldobler, B., & Gronenberg, W. (1998). Ameisen - Leben in einer Welt von Duft· und Berührungsreizen. E-neuroforum, 4(3). doi:10.1515/nf-1998-0305
• Ehmer, B., & Gronenberg, W. (1997). Antennal muscles and fast antennal movements in ants. Journal of Comparative Physiology - B Biochemical, Systemic, and Environmental Physiology, 167(4), 287-296.
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  Abstract: The antennal movements of eight ant species (subfamilies Ponerinae, Myrmicinae, and Formicinae) are examined by high-frequency videograplly. They show a wide range of antennal velocities which is generated by antennal muscles composed of particularly diverse muscle fibers. Fiber diameter, sarcomere length and histochemically assessed myosin ATPase activity suggest that some thin fibers are fairly slow, while the bulk of antennal muscle fibers show intermediate or fast properties. These morphological properties correlate with the antennal movement velocities measured for the respective species. Based on their morphology, the fibers that generate the fast antennal retraction in some trapjaw ants appear particularly fast and comprise the shortest sarcomeres yet described (1.1 μm).
• Ehmer, B., & Gronenberg, W. (1997). Proprioceptors and fast antennal reflexes in the ant Odontomachus (Formicidae, Ponerinae). Cell and Tissue Research, 290(1), 153-165.
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  PMID: 9377635;Abstract: In ants, antennal movements support the stimulus perception of olfactory and mechanosensory sensilla, most of which are located on the distal part of the antenna. In addition, sensory hair plates, campaniform sensilla, and Janet's organ provide the ant with proprioceptive information about the position, velocity, and acceleration of their antennae. We describe the morphology of these proprioceptors and their afferent neurons with special reference to the trap-jaw ant genus Odontomachus. All these sensory neurons terminate in the dorsal lobe, the part of the brain that also contains antennal motor neurons and that controls antennal movements. Neurons originating from campaniform sensilla and Janet's organ send additional collaterals into the subesophageal ganglion. Particularly fast antennal movements occur during protective withdrawal of the antenna. Under natural conditions, antennal retraction in Odontomachus always precedes the rapid mandible strike. We have found no indication of monosynaptic coupling between the antennal proprioceptive afferents and the trigger motor neurons that release the mandible strike. Instead, complex neuronal interactions in the involved neuromeres are more likely to control the timing of the two reflexes. The normal behavioral sequence of antennal retraction can be reversed by artificially releasing the mandible strike earlier than normal. The significance of fast antennal reflexes and of proprioceptive control is discussed.
• Gronenberg, W., Paul, J., Just, S., & Hölldobler, B. (1997). Mandible muscle fibers in ants: Fast or powerful?. Cell and Tissue Research, 289(2), 347-361.
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  PMID: 9211838;Abstract: Ants use their mandibles for catching prey, cracking seeds, cutting leaves, or for the construction of nests and the tender care of brood. The functional morphology of the mandibles reflect the species' adaptations to particular foraging habits and social life. The versatility and specialization of the mandibles depend directly on the design and physiology of the mandible closer muscles and their component fibers. A comparative video analysis of the closing movements of ant mandibles revealed that the maximal velocity varies considerably among species. The speed is correlated with the morphology of the mandible closer muscle, the largest muscle in ants. It is composed of two morphologically very distinct fiber types: long fibers with short sarcomeres (sarcomere length approximately 2 μm) showing all the structural attributes of fast muscle fibers, and shorter fibers with longer sarcomeres (sarcomere length approximately 5 μm) exhibiting the characteristics of slow and powerful fibers. Ants with fast-moving mandibles have a very high proportion of fast closer fibers, whereas the muscles of ants that cannot perform fast mandible movements have only a few or no fast fibers at all. Fast fibers always attach directly to the solid apodeme, while slow fibers often attach to thin apodeme threads. We suppose that the latter kind of fiber attachment is disadvantageous for fast contracting fibers but helps the ants to make better use of the space in the head capsule.
• Gronenberg, W. (1996). Fast actions in small animals: Springs and click mechanisms. Journal of Comparative Physiology A: Sensory, Neural, and Behavioral Physiology, 178(6), 727-734.
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  Abstract: Small animals that jump or perform predatory strikes depend on much higher limb accelerations than larger animals. To overcome the temporal restrictions of muscle contraction, some arthropod muscles slowly load spring-like structures with potential energy. In flight, sound generation, jumping, or predatory strikes arthropods employ different strategies to transform muscular action to the desired movement. Click mechanisms control the frequency of oscillating spring - muscle systems while other accessory structures such as snap mechanism or latches with trigger muscles determine the stability and control the timing of the instantaneous discharge in catapult mechanisms. muscles which is somewhere between 1 ms and 20 ms (Huxley 1965, 1974). The present account explains how these small animals are able to cope with this dilemma.
• Gronenberg, W. (1996). NEUROETHOLOGY OF ANTS. Naturwissenschaften, 83(1), 15-27. doi:10.1007/bf01139305
• Gronenberg, W. (1996). Neuroethology of ants. Naturwissenschaften, 83(1), 15-27.
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  Abstract: Despite the wealth of information produced by the flourishing ethology of ants, little is known about the neural mechanisms that control their behavior. This review summarizes the starting points of an emerging field of ant neuroethology which so far has mainly been concerned with basic sensory and motor information processing. Projects involving behavioral modulation by visual and mechanosensory input as well as reflex pathways, motor control, and the structure and function of ant muscles are illustrated. The distinct structural properties of the ant brain suggest challenging perspectives that address the higher 'cognitive' functions which set the ants apart from socially less highly organized insects.
• Gronenberg, W. (1996). The trap-jaw mechanism in the dacetine ants Daceton armigerum and Strumigenys sp.. Journal of Experimental Biology, 199(9), 2021-2033.
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  Abstract: Ants of three different subfamilies, among them the tribe Dacetini, have evolved very fast snapping mandibles called trap-jaws. The two dacetine genera examined, the large Daceton and the small Strumigenys, employ the same mechanism for their mandible strike. Video analysis reveals that, in Strumigenys sp., the strike takes less than 2.5 ms. It is released within 5 ms by contact of trigger hairs on the labrum. The ants employ a catapult mechanism to generate such a fast movement. Before the strike, the mandibles are opened wide and locked in the open position by the labrum, which functions as a latch. They stay open even when the large slow closer muscles contract. Upon trigger hair stimulation, the labrum is pulled backwards by a small, fast trigger muscle. The mandibles are thus freed from the catch and close rapidly. This reflex is controlled by giant sensory and motor neurones in the labral neuromere that are probably monosynaptically coupled. The short latency of the reflex thus results from the combination of a catapult mechanism, fast trigger muscles, high neuronal conduction velocities and small synaptic delays. Comparison with the trap-jaw mechanism of the ant genus Odontomachus reveals a remarkable example of convergent evolution.
• Gronenberg, W., & Ehmer, B. (1996). The mandible mechanism of the ant genus Anochetus (Hymenoptera, Formicidae) and the possible evolution of trap-jaws. Zoology, 99(3), 153-162.
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  Abstract: Ants of the genus Anochetus are able to close their mandibles extremely rapidly when specialized trigger hairs contact a prey object. This so-called trap-jaw strike takes less than 2.5 ms and the entire reflex can be performed within 5 ms. The trap-jaw design is based on a catapult mechanism composed of a large slow closer and a small fast trigger muscle. The reflex is controlled by giant sensory and motor neurons and is very similar to that described for the ant Odontomachus. We discuss the similarities and differences between the two genera and propose a sequence of steps that may have led to the evolution of trap-jaws. © by Gustav Fischer Verlag Jena.
• Gronenberg, W., Heeren, S., & Hölldobler, B. (1996). Age-dependent and task-related morphological changes in the brain and the mushroom bodies of the ant Camponotus floridanus. Journal of Experimental Biology, 199(9), 2011-2019.
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  Abstract: Based on a brief description of the general brain morphology of Camponotus floridanus, development of the brain is examined in ants of different ages (pupa to 10 months). During this period, brain volume increases by approximately 20% while the antennal lobes and the mushroom body neuropile show a more substantial growth, almost doubling their volume. In addition to the age-dependent changes, the volume of the mushroom body neuropile also increases as a consequence of behavioural activity associated with brood care and foraging. Foraging activity may lead to a more than 50% additional increase in mushroom body neuropile volume. It is unlikely that the growth of mushroom body neuropile results from cell proliferation because no neurogenesis could be observed in adult ant brains.
• Gronenberg, W. (1995). The fast mandible strike in the trap-jaw ant Odontomachus - I. Temporal properties and morphological characteristics. Journal of Comparative Physiology A, 176(3), 391-398.
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  Abstract: Ants of the ponerine genus Odontomachus employ a trap-jaw mechanism that allows them to instantaneously close their long, sturdy mandibles to catch prey or to defend themselves. Photoelectric scanning has revealed that these trap-jaws can be closed in less than 0.5 ms and that they decelerate before they collide with each other. The mandible strike is released in a reflexlike action when particular trigger hairs are touched. This reflex takes 4 to 10 ms and is probably the fastest reflex yet described for any animal. This speed is based on a catch mechanism in the mandible joint that keeps the extended mandibles open during contraction of the powerful closer muscle and allows the potential energy it produces to be stored within cuticular elements, apodemes, and the closer muscle itself. During a strike a relatively small specialized trigger muscle unlocks the catch, instantaneously releasing the stored energy to accelerate the mandible. © 1995 Springer-Verlag.
• Gronenberg, W. (1995). The fast mandible strike in the trap-jaw ant Odontomachus - II. Motor control. Journal of Comparative Physiology A, 176(3), 399-408.
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  Abstract: Ants of the ponerine genus Odontomachus employ a trap jaw mechanism for prey catching or defense. The mandible strike is released within less than 10 ms upon stimulation of particular mechanosensory trigger hairs. It is based on the storage of mechanical energy produced by the large but slow mandible closer muscle which cocks the mandible several seconds in advance of the strike. The strike is released from the catch by a small trigger muscle composed of tubular fibers. It features fast potentials and highly synchronized activation of all its muscle fibers only a few milliseconds in advance of the strike. The trigger muscle is supplied by two unusually large motor neurons that are enclosed in a glial sheath. The trap jaw action is thus controlled by a system composed of 2 giant sensory and 2 giant motor neurons on either side. The giant neurons are most likely monosynaptically coupled. The large axon diameter and the synaptic coupling result in high conduction velocity which underlies the very fast mandible reflex. The reflex activity is modulated by antennal and other sensory input probably converging onto the large dendritic trees of the trigger motor neurons. © 1995 Springer-Verlag.
• Milde, J. J., Strausfeld, N. J., Strausfeld, N. J., Milde, J. J., & Gronenberg, W. (1995). Oculomotor control in calliphorid flies: organization of descending neurons to neck motor neurons responding to visual stimuli.. The Journal of comparative neurology, 361(2), 267-84. doi:10.1002/cne.903610206
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  In insects, head movements are mediated by neck muscles supplied by nerves originating in the brain and prothoracic ganglion. Extracellular recordings of the nerves demonstrate units that respond to visual stimulation of the compound eyes and to mechanosensory stimulation of the halteres. The number of neck muscles required for optokinetic eye movements in flies is not known, although in other taxa, eye movements can involve as few as three pairs of muscles. This study investigates which neck motor neurons are likely to be involved in head movements by examining the relationships between neck muscle motor neurons and the terminals visiting them from approximately 50 pairs of descending neurons. Many of these descending neurons have dendrites in neuropils that are associated with modalities other than vision, and recording show that visual stimuli activate only a few neck motor neurons, such as the sclerite depressor neurons, which respond to local or wide-field, directionally specific motion, as do a subset of descending neurons coupled to them. The results suggest that, like in the vertebrate eye or the retinas of jumping spiders, optokinetic head movements of flies require only a few muscles. In addition to the importance of visual inputs, a major supply to neck muscle centers by nonvisual descending neurons suggests a role for tactile, gustatory, and olfactory signals in controlling head position.
• Strausfeld, N. J., Strausfeld, N. J., Gronenberg, W., & Gilbert, C. (1995). Oculomotor control in calliphorid flies: head movements during activation and inhibition of neck motor neurons corroborate neuroanatomical predictions.. The Journal of comparative neurology, 361(2), 285-97. doi:10.1002/cne.903610207
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  In tethered flying flies, moving contrast gratings or small spots elicit head movements which are suited to track retinal images moving at velocities up to 3,000 degrees/sec (about 50 Hz contrast frequency for gratings of spatial wavelength 15 degrees). To investigate the neural basis of these movements we have combined videomicroscopy with electrophysiological stimulation and recording to demonstrate that excitation of prothoracic motor neurons projecting in the anterodorsal (ADN) and frontal nerves (FN), respectively, generates the yaw and roll head movements measured behaviorally. Electrical stimulation of the ADN produces head yaw. The visual stimuli which excite the two ADN motor neurons (ADN MNs) are horizontal motion of gratings or spots moving clockwise around the yaw axis in the case of the right ADN (counterclockwise for left ADN). Activity is inhibited by motion in the opposite direction. Spatial sensitivity varies in the yaw plane with a maximum between 0 degree and 40 degrees ipsilaterally, but both excitation and inhibition are elicited out to 80 degrees in the ipsilateral and contralateral fields. ADN MNs respond to contrast frequencies up to 15-20 Hz, with a peak around 2-4 Hz for grating motion in the excitatory or inhibitory directions. Electrical stimulation of the FN primarily elicits roll down to the ipsilateral side. The one FN MN consistently driven by visual stimulation is excited by downward motion and inhibited by upward motion at 80 degrees azimuth in the ipsilateral visual field. At -80 degrees contralateral, visual motion has the opposite effect: Upward is excitatory and downward is inhibitory. The FN MN is tuned to contrast frequencies in the same range as the ADN MNs, with peak sensitivity around 4 Hz. The functional organization of inputs to the ADN and FN is discussed with respect to identified visual interneurons and parallel pathways controlling motor output.
• Gronenberg, W., & Tautz, J. (1994). The sensory basis for the trap-jaw mechanism in the ant Odontomachus bauri. Journal of Comparative Physiology A, 174(1), 49-60.
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  Abstract: Ants of the ponerine genus Odontomachus have evolved a mechanism that allows them to instantaneously close their long mandibles to catch prey or defend themselves. This trap-jaw action is triggered by contact of trigger hairs with a potential prey item. Two of these long mechanosensory hair sensilla reside proximally on each mandible and are supplied by giant sensory cells. Extracellular recordings demonstrate that the sensory cells respond to tactile stimulation. Their phasic responses encode amplitude and velocity of hair-deflection away from the midline, but not hair position. The discharge of action potentials follows stimulus frequencies of more than 300 Hz. During sinusoidal stimulation, the cells adapt very little, sustain discharge rates of more than 200 Hz for more than 20 s, and reach peak spike rates of about 450 Hz. The afferent axons of these sensory cells give rise to huge axon terminals within the suboesophageal ganglion. One of the afferents has a prominent contralateral branch, the other is confined to ipsilateral neuropil. Anatomical data indicate that the 4 afferents may be coupled and may serve as the substrate for a very fast reflex. © 1994 Springer-Verlag.
• Hölldobler, B., Braun, U., Gronenberg, W., Kirchner, W. H., & Peeters, C. (1994). Trail communication in the ant Megaponera foetens (Fabr.) (Formicidae, Ponerinae). Journal of Insect Physiology, 40(7), 585-593.
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  Abstract: The African ponerine ant Megaponera foetens conducts well organized group raids on termites. Observations of raids in western Africa, together with laboratory experiments, confirm previous reports that recruitment is based on a scout system and trail pheromones. One component of the trail signal derives from the poison gland. We discovered a second trail pheromone which originates from the pygidial gland. The latter secretions have a more powerful recruitment effect whereas poison gland secretions contain a much longer-lasting orientation cue. The secretions of the sternal gland, Dufour's gland and hind gut contents do not elicit trail-following. The long bristles surrounding the tip of the gaster are innervated and probably serve as mechano-receptors during trail-laying. No evidence could be found that the conspicuous stridulatory sounds produced by the ant columns serve intraspecific communication. In the field, stridulation by raiding ants was observed exclusively as a response to disturbance. In the laboratory, strong vibrations of the ground as well as air currents elicit stridulation. Air/CO2 mixtures are significantly more efficient in releasing stridulation compared to pure air. We suggest that these sounds are aposematic warning signals aimed at potential vertebrate predators. © 1994.
• Gronenberg, W., & Peeters, C. (1993). Central projections of the sensory hairs on the gemma of the ant Diacamma: substrate for behavioural modulation?. Cell & Tissue Research, 273(3), 401-415.
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  Abstract: In the ant genus Diacamma, all workers eclose from their cocoons with little clublike thoracic appendages, called gemmae. Whether these gemmae are mutilated determines individual behaviour, and ultimately reproductive role, in two of the three species examined. The gemmae are covered with sensory hairs, which probably serve a mechanoreceptive function. The sensory afferents arising from these hairs were stained and traced into the central nervous system (CNS). They feature widely distributed collaterals invading all three thoracic ganglia as well as the suboesophageal and the second abdominal ganglia. The multisegmental arborization pattern of the gemma afferents is very similar to that of wing-hair afferents of other ants (queens and males) or other insects in general. This implies that gemmae and wings are homologous structures. We discuss the morphology of the gemma afferents with respect to their possible involvement in the behavioural changes associated with mutilation. The neuronal processing may be modulated by (1) the decrease of sensory input onto interneurons (suggested by the afferents' extensive arborizations); or (2) by the effect of neuromodulatory substances (suggested by the finding that terminals occur within the cell body rind of the ganglion). © 1993 Springer-Verlag.
• Gronenberg, W., Tautz, J., & Hölldobler, B. (1993). Fast trap jaws and giant neurons in the ant Odontomachus. Science, 262(5133), 561-563.
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  PMID: 17733239;Abstract: Ants of the ponerine genus Odontomachus use a trap jaw mechanism when hunting fast prey. When particular trigger hairs, located on the inner edge of the mandibles, are touched by prey, the jaws close extremely rapidly and trap the target. This trap jaw response lasts only 0.33 to 1 millisecond. Electrophysiological recordings demonstrated that the trigger hairs function as mechanoreceptors. Associated with each trigger hair are large sensory cells, the sensory axons of which measure 15 to 20 micrometers in diameter. These are among the largest sensory neurons, and their size implies that these axons conduct information very rapidly.
• Strausfeld, N. J., Strausfeld, N. J., & Gronenberg, W. (1992). Premotor descending neurons responding selectively to local visual stimuli in flies.. The Journal of comparative neurology, 316(1), 87-103. doi:10.1002/cne.903160108
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  The responses of dorsal descending neurons suggest great versatility of the visual system in detecting features of the visual world. Although wide-field motion-sensitive neurons respond to symmetric visual flow fields presented to both eyes, other neurons are known to respond selectively to asymmetric movement of the visual surround. The present account distinguishes yet a third class of descending neurons (DNs) that is selectively activated by local presentation of moving gratings or small contrasting objects. Excitation of these DNs in response to local motion contrasts with their inhibitory responses to wide-field motion. The described DNs invade dorsal neuropil of the pro- and mesothoracic ganglia where they converge with other morphologically and physiologically characterized descending elements. Axon collaterals of DNs visit thoracic neuropil containing the dendrites of motor neurons supplying indirect neck and flight muscles. The present results are discussed with respect to the organization of small-field retinotopic outputs from the lobula, and with respect to the parallel projection of many information channels from the brain to the neck and flight motors.
• Strausfeld, N. J., Strausfeld, N. J., & Gronenberg, W. (1991). Descending pathways connecting the male-specific visual system of flies to the neck and flight motor.. Journal of comparative physiology. A, Sensory, neural, and behavioral physiology, 169(4), 413-26. doi:10.1007/bf00197654
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  During sexual pursuit, male flies Sarcophaga bullata, stabilize the image of a pursued target on the dorso-frontal acute zone of their compound eyes. By retinotopic projection, this region is represented in the upper frontal part of the lobula where it is sampled by ensembles of male-specific motion- and flicker-sensitive interneurons. Intracellular recordings of descending neurons, followed by biocytin injection, demonstrate that male-specific neurons are dye-coupled to specific descending neurons and that the response characteristics of these descending neurons closely resemble those of male-specific lobula neurons. Such descending neurons are biocytin-coupled in the thoracic ganglia, revealing their connections with ipsilateral frontal nerve motor neurons supplying muscles that move the head and with contralateral basalar muscle motor neurons that control wing beat amplitude. Recordings from neck muscle motor neurons demonstrate that although they respond to movement of panoramic motion, they also selectively respond to movement of small targets presented to the male-specific acute zone. The present results are discussed with respect to anatomical and physiological studies of sex-specific interneurons and with respect to sex-specific visual behavior. The present study, and those of the two preceding papers, provide a revision of Land and Collett's hypothetical circuit underlying target localization and motor control in males pursuing females.
• Gronenberg, W. (1990). The organization of plurisegmental mechanosensitive interneurons in the central nervous system of the wandering spider Cupiennius salei. Cell and Tissue Research, 260(1), 49-61.
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  PMID: 2340585;Abstract: In spiders the bulk of the central nervous system (CNS) consists of fused segmental ganglia traversed by longitudinal tracts, which have precise relationships with sensory neuropils and which contain the fibers of large plurisegmental interneurons. The responses of these interneurons to various mechanical stimuli were studied electrophysiologically, and their unilateral or bilateral structure was revealed by intracellular staining. Unilateral interneurons visit all the neuromeres on one side of the CNS. They receive mechanosensory input either from a single leg or from all ipsilateral legs via sensory neurons that invade leg neuromeres and project into specific longitudinal tracts. The anatomical organization of unilateral interneurons suggests that their axons impart their information to all ipsilateral leg neuromeres. Bilateral interneurons are of two kinds, symmetric and asymmetric neurons. The latter respond to stimulation of all legs on one side of the body, having their dendrites amongst sensory tracts of the same side of the CNS. Anatomical evidence suggests that their terminals invade all four contralateral leg neuromeres. Bilaterally symmetrical plurisegmental interneurons have dendritic arborizations in both halves of the fused ventral ganglia. They respond to the stimulation of any of the 8 legs. A third class of cells, the ascending neurons have unilateral or bilateral dendritic arborizations in the fused ventral ganglia and show blebbed axons in postero-ventral regions of the brain. Their response characteristics are similar to those of other plurisegmental interneurons. Descending neurons have opposite structural polarity, arising in the brain and terminating in segmental regions of the fused ventral ganglia. Descending neurons show strong responses to visual stimulation. Approximately 50% of all the recorded neurons respond exclusively to stimulation of a single type of mechanoreceptor (either tactile hairs, or trichobothria, or slit sensilla), while the rest respond to stimulation of a variety of sensilla. However, these functional differences are not obviously reflected by the anatomy. The functional significance of plurisegmental interneurons is discussed with respect to sensory convergence and the coordination of motor output to the legs. A comparison between the response properties of certain plurisegmental interneurons and their parent longitudinal tracts suggests that the tracts themselves do not reflect a modality-specific organization. © 1990 Springer-Verlag.
• Strausfeld, N. J., Strausfeld, N. J., & Gronenberg, W. (1990). Descending neurons supplying the neck and flight motor of Diptera: organization and neuroanatomical relationships with visual pathways.. The Journal of comparative neurology, 302(4), 954-72. doi:10.1002/cne.903020419
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  In dipterous insects, a volume of behavioral and electrophysiological studies promote the contention that three wide-field motion-sensitive tangential neurons provide a necessary and sufficient input to specific channels that drive the torque motor during flight. The present studies describe the results of neuroanatomical investigations of the relationships between motion-sensitive neuropil in the fly optic lobes and descending neurons that arise from a restricted area of the brain and supply segmental neck and flight motor neuropil. The present observations resolve at least 50 pairs of descending neurons supplying flight motor centers in the thoracic ganglia. The majority of descending neurons receive a distributed output from horizontal motion-sensitive neurons. However, the same descending neurons are also visited by numerous small-field retinotopic neurons from the lobula plate as well as hitherto undescribed small tangential neurons. Neuroanatomical studies, using cobalt, Golgi, and Texas red histology, demonstrate that these smaller inputs onto descending neurons have dendrites that are organized at specific strata in retinotopic neuropil and that these correspond to horizontal and vertical motion sensitivity layers. Conclusions that only a restricted number of wide-field neurons are necessary and sufficient for visually stabilized flight may be premature. Rather, neuroanatomical evidence suggests that descending neurons to the flight motor may each be selectively tuned to specific combinations of wide- and small-field visual cues, so providing a cooperative descending network controlling the rich repertoire of visually evoked flight behavior.
• Strausfeld, N. J., Strausfeld, N. J., & Gronenberg, W. (1990). Descending neurons supplying the neck and flight motor of Diptera: physiological and anatomical characteristics.. The Journal of comparative neurology, 302(4), 973-91. doi:10.1002/cne.903020420
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  In Diptera, dorsal neuropils of the pro-, meso-, and metathoracic ganglia supply motor neurons to neck and flight muscles. Motor circuits are supplied by more than 50 pairs of descending neurons (DNs) whose dendritic trees in the brain are restricted to dorsal neuropils of the deutocerebrum where they are grouped together into discrete clusters. Each cluster is visited by wide-field motion-sensitive neurons and by morphologically small-field retinotopic elements. This organization suggests that flight descending neurons should respond to complex stimuli reflecting panoramic movement and small-field motion. Intracellular recordings, combined with dye filling, confirm this. Certain descending neurons responding to visual flow fields terminate bilaterally in superficial pterothoracic neuropils, at the level of indirect (power) flight muscle motor neurons. Other DNs terminate laterally, and provide segmental collaterals to areas containing neck and direct (steering) flight muscle motor neurons. Such DNs are activated by wide-field directional stimuli corresponding to pitch, roll, or yaw, and to small-field stimuli. Appropriate directional mechanosensory stimuli also activate dorsal descending neurons. The significance of dorsal descending neurons for the control of flight is discussed and compared with studies on course deviation neurons in other insects. It is suggested that, in Diptera, dorsal descending neurons may separately be involved in the control of velocity, stabilization, and steering manoeuvres.
• Gronenberg, W. (1989). Anatomical and physiological observations on the organization of mechanoreceptors and local interneurons in the central nervous system of the wandering spider Cupiennius salei. Cell and Tissue Research, 258(1), 163-175.
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  PMID: 2805041;Abstract: In the wandering spider Cupiennius salei, the functional neuroanatomy of leg mechanosensory receptor neurons and interneurons associated with a single leg neumere was investigated by combined intracellular recording and Lucifer yellow ionophoresis. Trichobothria axons that selectively respond to air currents and to low-frequency airborne vibrations have arborizations restricted to ventral regions of the appropriate leg neuromere. Receptor afferents that respond selectively to substrateborne vibrations are distributed ventrally in the corresponding leg neuromere and extend into certain interganglionic tract neuropiles. Golgi impregnation and intracellular dye filling show that local interneurons originate in ventral sensory neuropiles of leg neuromeres and ascend dorsally to terminate amongst dendrites of motor neurons. Local interneurons generally show higher thresholds for vibration stimuli than do receptors. Local interneurons typically receive inputs from one or several types of receptors. Some respond to stimulation of a single leg, others respond to stimulation of several legs on the same side of the body. The functional morphology of the receptor afferents is correlated with known physiological characteristics of slit sensilla and trichobothria. Structure and activity of the local interneurons are compared with analogous interneurons in other arthropods. © 1989 Springer-Verlag.
• Gronenberg, W. (1987). Anatomical and physiological properties of feedback neurons of the mushroom bodies in the bee brain.. Experimental biology, 46(3), 115-125.
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  PMID: 3582581;Abstract: "Feedback neurons" in the bee's mushroom body were recorded from and filled iontophoretically with either Lucifer Yellow or cobalt-hexammino-chloride (III). The neurons have complex shapes arborizing in one, or sometimes two layers of the alpha-lobe, and sometimes in the beta-lobe and pedunculus. Their axons project via the protocerebral-calycal-tract into the calyx lip and collar zones, ending as blebbed processes. Additionally these neurons also project around the alpha-lobe into the protocerebrum. More than 70% of the recorded neurons were multimodal responding to several test-stimuli. These include: light, airstreams towards the antennae and the abdomen, various odors, water and sugar-water presented to the antennae and proboscis, and mechanical stimulation of the legs. Responses were usually excitatory and in many cases showed aftereffects which lasted for many seconds. Some neurons showed spontaneous changes in their response-properties. There appeared to be no clear match between the modality of any one neuron and the anatomical features of its dendritic regions. The possible functional rôles of feedback neurons in learning and behaviour are discussed with particular reference to their structural identity as a recurrent loop from the lobes to the calyces.
• Gronenberg, W. (1986). Physiological and anatomical properties of optical input-fibres to the mushroom body in the bee brain. Journal of Insect Physiology, 32(8), 695-699,701-704.
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  Abstract: More than 150 neurones in the nushroom body area of the bee brain were recorded and stained intracellularly with either Lucifer Yellow or Cobalt-Hexamminochloride (III). Among them 12 neurones have been characterized physiologically and anatomically which connect the medulla and the lobula with the mushroom bodies. All neurones responded to stationary or moving light stimuli exclusively. Movement-sensitive neurones were all direction-selective. Excitatory and inhibitory responses occurred in response to moving stripe patterns in the preferred and null directions respectively. Anatomically, the neurones could be clearly distinguished as belonging to three types depending on their input features in the optic lobes: (a) Neurones with small dendritic fields (up to 100 μm) in the lobula; (b) Neurones with large dendritic fields (up to 400 μm) in the lobula; (c) Neurones with small dendritic fields (up to 100 μm) in the medulla. The axons of all three cell types run from the optic lobes on each side to the outer ring tract around the pedunculus-calyx-transition and arborize in the collar region of the ipsilateral calyces. Additional branches invading the basal ring of the calyces had been observed; endings in the lip region were not found. The endings in the calyces often exhibited bleb-like specializations indicating their presynaptic nature. Retinotopic organization of the optic inputs into the calyces could not be proven. The results are compared with the characteristics of multimodal mushroom body output fibres and are discussed in context with the complex information processing and storage functions ascribed to the mushroom bodies. © 1986.

Presentations

• Davidowitz, G., Favela, A., Allen, N., Gronenberg, W., & Moore, A. F. (2015, January). Male and female allocation strategies to head function is mediated by resource limitation. Society for Integrative and Comparative Biology (SICB). West Palm Beach, Florida: SICB.

Poster Presentations

• Gronenberg, W., & Godfrey, K. (2017, January). Reliance on social information and trail pheromone processing in two species of Dolichoderinae ants. Society for Comparative and Integrative Biology Annual meeting. New Orleans: Society for Comparative and Integrative Biology.
• Gronenberg, W., & Riveros, A. J. (2017, June). Riveros AJ, Leonard AS, Gronenberg W, Papaj DR (2017) Timing and composition of bimodal signals underlie diversity of performance during classical conditioning in restrained bumblebees.. Gordon Research Conference ‘Neuroethology: Behavior, Evolution and Neurobiology. Geneva, Switzerland: Gordon Conferences.
• Gronenberg, W., Carhart, B., Hutchison, D., & Manjom, I. (2016, April). Chemosensory pathways in spiders and their kin.. XII International Congress of Neuroethology. Montevideo, Uruguay: International Society for Neuroethology.
• Keating, R., Nguyen, D. M., Davidson-Knapp, R., Sadatmousavi, L., & Gronenberg, W. (2016, April). Linking Variation in Learning Ability with Regional Brain Metabolism in Foragers of the Ant Novomessor cockerelli. XII International Congress of Neuroethology. Montevideo, Uruguay: International Society for Neuroethology.
• Gronenberg, W., & Gowda, V. (2015, Fall). Comparative analysis of brain and brain component size in different honey bee species. Entomological Society of America. Minneapolis,MN: Entomological Society of America.
• Jones, B., Leonard, A. S., Papaj, D. R., & Gronenberg, W. (2011, August). The role of multimodal experience in bumble bee brain development. Animal Behavior Society, Annual Meeting. Bloomington, IN: Animal Behavior Society.
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  won Honorable Mention for Best Poster