Nicole Elise Leitner

Interests

Research

I use D. melanogaster to explore the gene pathways regulating neuronal development. My research focuses on how the intersection of different developmental pathways shapes the pathfinding decisions of growing neurons, how these mechanisms vary both across and within individuals, and how this variation influences behavior.

Courses

Scholarly Contributions

Journals/Publications

• Vernier, C. L., Leitner, N., Zelle, K. M., Foltz, M., Dutton, S., Liang, X., Halloran, S., Millar, J. G., & Ben-Shahar, Y. (2023). A pleiotropic chemoreceptor facilitates the production and perception of mating pheromones. iScience, 26(1).
• Leitner, N., & Ben-shahar, Y. (2020). The neurogenetics of sexually dimorphic behaviors from a postdevelopmental perspective.. Genes, brain, and behavior, 19(2), e12623. doi:10.1111/gbb.12623
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  Most sexually reproducing animal species are characterized by two morphologically and behaviorally distinct sexes. The genetic, molecular and cellular processes that produce sexual dimorphisms are phylogenetically diverse, though in most cases they are thought to occur early in development. In some species, however, sexual dimorphisms are manifested after development is complete, suggesting the intriguing hypothesis that sex, more generally, might be considered a continuous trait that is influenced by both developmental and postdevelopmental processes. Here, we explore how biological sex is defined at the genetic, neuronal and behavioral levels, its effects on neuronal development and function, and how it might lead to sexually dimorphic behavioral traits in health and disease. We also propose a unifying framework for understanding neuronal and behavioral sexual dimorphisms in the context of both developmental and postdevelopmental, physiological timescales. Together, these two temporally separate processes might drive sex-specific neuronal functions in sexually mature adults, particularly as it pertains to behavior in health and disease.
• Leitner, N., & Dornhaus, A. (2019). Dynamic task allocation: how and why do social insect workers take on new tasks?. Animal Behaviour, 158, 47-63. doi:10.1016/j.anbehav.2019.09.021
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  Complex living systems often exist in noisy environments and must have a way to respond to change. In social insects, the colony itself is a complex system composed of dozens to millions of essentially autonomous workers. Studying the behaviour of these workers in response to experimental disturbance provides insight into the mechanisms by which colonies, and complex systems in general, can achieve flexibility. Here, we explore dynamic task allocation within colonies of Temnothorax rugatulus ants by separately increasing the demand for three different types of work: nest maintenance, brood care and foraging. We investigate (1) whether colonies respond to dynamic task demand and the timeline of their responses, (2) whether the colony achieves this flexibility by recruiting new workers to these tasks or modulating individual worker effort and (3) the rules by which individual workers switch tasks. We found that T. rugatulus ants are responsive to colony perturbation, yet the means by which they achieve this flexibility are task dependent, as is the time it takes them to respond. Flexibility is achieved both by the increased effort of already active workers and the recruitment of new workers to the focal task. We suggest that newly recruited workers may come from task-specific reserve pools of unemployed workers: roaming ‘walkers’ appear to be a generalized reserve force for most tasks except for brood care, while previously inactive workers might act as a specialized reserve pool for brood care and be prompted to engage in this task when they locally encounter brood.
• Leitner, N., Charbonneau, D., Dornhaus, A., Gronenberg, W., & Leitner, N. E. (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.
• Leitner, N., Dornhaus, A., Leitner, N. E., & Lynch, C. (2019). Ants in isolation: obstacles to testing worker responses to task stimuli outside of the colony context. Insectes Sociaux, 66(3), 343-354. doi:10.1007/s00040-019-00692-1
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  In social insects, division of labor is commonly thought to be driven by differences among workers in their sensitivity, or response thresholds, to task-related stimuli. Despite the wide use of this mechanism throughout social insect research, actual empirical evidence for these thresholds is comparatively scarce. Here, we attempt to fill this empirical gap by testing individual task stimulus response thresholds, their consistency over time, and their relation to behavior in Temnothorax rugatulus ants. We also explored morphological differences in the antenna as one potential neural mechanism generating differences in sensitivity, and thus response threshold variation, across workers. Ants were exposed to different amounts of hungry brood, fungal spores, or sugar— stimuli that appear to drive brood care, grooming, and foraging behavior, respectively. Our measures of response thresholds were not repeatable across two trials for any of the three tested stimuli. In addition, responses to different stimulus intensities (possible response thresholds) were not associated with worker task allocation in the colony with the exception of brood care, in which case the results directly contradicted what the response threshold hypothesis predicts. Workers from different task groups also did not differ in their latency to respond to these stimuli or in the duration of their response. Sensilla density varied across workers but did not predict our measures of response thresholds to any of the tested stimuli. Though this is not what the response threshold hypothesis would have predicted, it is possible that testing ants in isolation may not accurately reflect their behavior in the colony, or that sensitivity to a task stimulus, alone, is not sufficient for driving division of labor. We suggest approaches to testing response thresholds that incorporate the roles of social context and competing task stimuli.
• Ramirez-esquivel, F., Leitner, N. E., Zeil, J., & Narendra, A. (2017). The sensory arrays of the ant, Temnothorax rugatulus.. Arthropod structure & development, 46(4), 552-563. doi:10.1016/j.asd.2017.03.005
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  Individual differences in response thresholds to task-related stimuli may be one mechanism driving task allocation among social insect workers. These differences may arise at various stages in the nervous system. We investigate variability in the peripheral nervous system as a simple mechanism that can introduce inter-individual differences in sensory information. In this study we describe size-dependent variation of the compound eyes and the antennae in the ant Temnothorax rugatulus. Head width in T. rugatulus varies between 0.4 and 0.7 mm (2.6-3.8 mm body length). But despite this limited range of worker sizes we find sensory array variability. We find that the number of ommatidia and of some, but not all, antennal sensilla types vary with head width. The antennal array of T. rugatulus displays the full complement of sensillum types observed in other species of ants, although at much lower quantities than other, larger, studied species. In addition, we describe what we believe to be a new type of sensillum in hymenoptera that occurs on the antennae and on all body segments. T. rugatulus has apposition compound eyes with 45-76 facets per eye, depending on head width, with average lens diameters of 16.5 μm, rhabdom diameters of 5.7 μm and inter-ommatidial angles of 16.8°. The optical system of T. rugatulus ommatidia is severely under focussed, but the absolute sensitivity of the eyes is unusually high. We discuss the functional significance of these findings and the extent to which the variability of sensory arrays may correlate with task allocation.