Hilary M. Lease

Interests

Teaching

Comparative Animal Physiology, Human Physiology, Physiological Adaptations to Environment

Research

Comparative Physiology, Physiological Ecology

Courses

Scholarly Contributions

Journals/Publications

• Lease, H. M., Botha, A., Fuller, A., Mitchell, D., & Hetem, R. S. (2019). Biologging subcutaneous temperatures to detect orientation to solar radiation remotely in savanna antelope: BOTHAet al.. Journal of Experimental Zoology Part A: Ecological and Integrative Physiology, 331(5), 267-279. doi:10.1002/jez.2267
• Lease, H. M., Kirchhof, S., Hetem, R. S., Miles, D. B., Mitchell, D., Müller, J., Rödel, M., Sinervo, B., Wassenaar, T., & Murray, I. W. (2017). Thermoregulatory behavior and high thermal preference buffer impact of climate change in a Namib Desert lizard. Ecosphere, 8(12). doi:10.1002/ecs2.2033
• Sebastian, K., Robyn, H., Lease, H. M., Miles, D., Mitchell, D., Muller, J., Rodel, M., Sinervo, B., Wassenaar, T., & Murray, I. W. (2017). Thermoregulatory behavior and high thermal preference buffer impact of climate change in a Namib Desert lizard. ECOSPHERE, 8(12), e02033.
• Murray, I. W., Fuller, A., Lease, H. M., Mitchell, D., & Hetem, R. S. (2016). Ecological niche separation of two sympatric insectivorous lizard species in the Namib Desert. JOURNAL OF ARID ENVIRONMENTS, 124, 225-232.
• Murray, I. W., Lease, H. M., Hetem, R. S., Mitchell, D., Fuller, A., & Woodborne, S. (2016). Stable isotope analysis of diet confirms niche separation of two sympatric species of Namib Desert lizard. INTEGRATIVE ZOOLOGY, 11(1), 60-75.
• Rey, B., Fuller, A., Hetem, R. S., Lease, H. M., Mitchell, D., & Meyer, L. (2016). Microchip transponder thermometry for monitoring core body temperature of antelope during capture. JOURNAL OF THERMAL BIOLOGY, 55, 47-53.
• Wolf, B. O., Murray, I. W., Mitchell, D., Lease, H. M., Hetem, R. S., & Fuller, A. (2015). Low field metabolic rates for geckos of the genus Rhoptropus may not be surprising. Journal of Arid Environments, 113, 35-42. doi:10.1016/j.jaridenv.2014.09.006
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  Abstract Geckos of the genus Rhoptropus are small diurnal lizards occurring in arid regions of Namibia and Angola, and are not well studied relative to other desert lizards. Rhoptropus afer has a field metabolic rate significantly lower than that of other desert lizards, but comparable studies have not been carried out in any other Rhoptropus species. We examined the field metabolic rate, water turnover, foraging behavior, and thermal biology of Bradfield's Namib day gecko, Rhoptropus bradfieldi , in the Namib Desert. This species occupies rocky habitats and feeds on arthropods via a sit-and-wait strategy. We found that it has a field metabolic rate (140 J d −1 ) that is 26% that of a typical desert lizard of the same size (540 J d −1 ). We also found that R. bradfieldi had a relatively high water influx rate (0.07 ml d −1 ) for its low rate of energy turnover, and suggest that a significant proportion of this water was sourced from fog. Active body temperatures varied between summer (32.7 ± 2.4 °C) and autumn (34.4 ± 2.5 °C), but in both seasons R. bradfieldi maintained high and stable body temperatures while active. Our study supports the idea that a minimal energy requirement could be widespread within Rhoptropus geckos.
• Murray, I. W., Lease, H. M., Hetem, R. S., & Fuller, A. (2014). Black wildebeest seek shade less and use solar orientation behavior more than do blue wildebeest.. Journal of thermal biology, 45, 150-6. doi:10.1016/j.jtherbio.2014.08.008
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  Many ungulates, including wildebeest, seek shade and orient their bodies relative to incoming solar radiation in order to reduce environmental heat loads. Blue (Connochaetes taurinus) and black wildebeest (Connochaetes gnou), which co-exist artificially in some reserves in South Africa, are thought to adopt different thermoregulatory behaviors to mitigate high environmental heat loads. However, whether or not blue and black wildebeest use different behaviors to reduce heat loads in regions where they co-occur has never previously been examined. We compared the shade seeking and solar orientation behavior of free-ranging blue and black wildebeest in summer at three locations in South Africa where both species co-occur. We found that blue wildebeest exhibited more shade seeking behavior than did black wildebeest at all times of day, at all study sites. Black wildebeest remained in the sun but were more likely than blue wildebeest to orient their bodies parallel to the sun at all study sites, a behavior which reduces the amount of surface area exposed to incoming radiation. Black wildebeest were most likely to employ parallel solar orientation during the hottest times of the day when the sun was not directly overhead (i.e., solar noon ± 1 hour). We thus demonstrate that co-occurring blue and black wildebeest use different thermoregulatory behaviors to reduce high heat loads. It is possible that the lack of shade in the historical distribution of black wildebeest led to selective pressure for reliance on solar orientation. Differences in thermoregulatory behavior can affect species-specific heat loads, habitat use, body mass, fitness and grazing activity. Such differences may also allow blue and black wildebeest to inhabit separate microclimates within the same habitat, provided there is sufficient heterogeneity in vegetation structure, potentially facilitating reproductive isolation.
• Seely, M. K., Mitchell, D., Lease, H. M., & Goelst, K. (2014). Evidence of temperature-independent metabolic rates in diurnal Namib Desert tenebrionid beetles. Physiological Entomology, 39(3), 254-262. doi:10.1111/phen.12070
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  To investigate whether the sensitivity to environmental temperature varies between nocturnal and diurnal species of tenebrionid beetle, the metabolic rates of three diurnal species (Onymacris plana Peringuey, Onymacris rugatipennis Haag and Physadesmia globosa Haag) and three nocturnal species (Epiphysa arenicola Penrith, Gonopus sp. and Stips sp.) of beetles from the Namib Desert are measured over a range of temperatures (15–40 °C) that are experienced by these beetles in their natural habitat. The diurnal species O. plana, O. rugatipennis and P. globosa exhibit temperature-independent metabolic rates (mean Q10 = 1.2) within temperature ranges that are ecologically relevant for diurnal desert beetles (30–40 °C). Onymacris plana, in particular, has a 20–40 °C rate–temperature slope (0.007 log10 mL O2 h−1 g−1 °C−1; Q10 = 1.1) that is less than half that of the other five beetle species (0.022–0.063 log10 mL O2 h−1 g−1 °C−1; Q10 ranges from 1.3–1.9), suggesting that O. plana is more metabolically independent of temperature than the other nocturnal and diurnal tenebrionids being investigated. Animals with metabolic rates that are decoupled from body temperature (or ambient temperature) may have an ecological advantage that allows them to exploit thermal and spatial niches during extreme temperature conditions.
• Smith, F. A., Murray, I. W., Martin, J., Lease, H. M., & Harding, L. E. (2014). Life in an extreme environment: a historical perspective on the influence of temperature on the ecology and evolution of woodrats. Journal of Mammalogy, 95(6), 1128-1143. doi:10.1644/13-mamm-s-070
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  The heterogeneous topography of the Great Basin province leads to one of the most climatically variable regions in the Northern Hemisphere. Along the southwestern edge lies Death Valley, an area of even more extreme climate and physiographic relief; Death Valley has the dubious distinction of being the hottest place on earth. Our research investigates the adaptive response of Neotoma (woodrats) to temperature fluctuations over the late Quaternary on the valley floor and along a nearby elevational and environmental gradient. By combining fieldwork on extant animals living on the valley floor with historical information from museum specimens and paleomiddens, we reconstruct the evolutionary histories of 2 species (N. lepida and N. cinerea) differing significantly in size and habitat preferences. Here, at the modern limit of both species' thermal and ecological thresholds, we find fluctuations in body size and range boundaries over the Holocene as climate shifted. Although N. cinerea is extirpated on the east side of the valley today, it was ubiquitous throughout the late Quaternary. Moreover, we find fundamental differences in the adaptive response of woodrats related to elevation and local microclimate. Modern work suggests the mechanism is physiological; exposure to consistently high temperatures leads to high mortality. Thus, high temperatures strongly restrict time available for the essential activities of foraging and mating. Our results illustrate the profound influence temperature has on all aspects of woodrat life history, ecology, distribution, and evolution.
• Lease, H. M., Klok, C. J., Kaiser, A., & Harrison, J. F. (2012). Body size is not critical for critical PO₂ in scarabaeid and tenebrionid beetles.. The Journal of experimental biology, 215(Pt 14), 2524-33. doi:10.1242/jeb.057141
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  Constraints on oxygen delivery potentially limit animal body size. Because diffusion rates are highly distance dependent, and because tracheal length increases with size, gas exchange was traditionally thought to be more difficult for larger insects. As yet the effect of body size on critical oxygen partial pressure (P(crit)) has not been measured for any clade of insect species for which there are interspecific data on tracheal scaling. We addressed this deficiency by measuring P(crit) over a 4150-fold mass range (ratio of largest to smallest species mean) of two families of Coleoptera (Tenebrionidae and Scarabaeidae). We exposed adult beetles to progressively lower oxygen levels and measured their ability to maintain CO(2) release rates. Absolute metabolic rates increased hypometrically with beetle body mass (M) at both normoxic (M(0.748)) and hypoxic (M(0.846)) conditions. P(crit), however, was independent of body size. Maximum overall conductances for oxygen from air to mitochondria (G(O(2),max)) matched metabolic rates as insects became larger, likely enabling the similar P(crit) values observed in large and small beetles. These data suggest that current atmospheric oxygen levels do not limit body size of insects because of limitations on gas exchange. However, increasing relative investment in the tracheal system in larger insects may produce trade-offs or meet spatial limits that constrain insect size.
• Wolf, B. O., & Lease, H. M. (2011). Lipid content of terrestrial arthropods in relation to body size, phylogeny, ontogeny and sex. Physiological Entomology, 36(1), 29-38. doi:10.1111/j.1365-3032.2010.00767.x
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  Energy storage in arthropods has important implications for survival and reproduction. The lipid content of 276 species of adult arthropods with wet mass in the range 0.2-6.13 g is determined to assess how lipid mass scales with body mass. The relative contribution of lipids to total body mass is investigated with respect to phylogeny, ontogeny and sex. The lipid content of adult insects, arachnids, and arthropods in general shows an isometric scaling relationship with respect to body mass (M )( Marthropod lipid =− 1.09 × Mdry 1.01 and Marthropod lipid =− 1.00 × Mlean 0.98 ). However, lipid allocation varies between arthropod taxa, as well as with sex and developmental stage within arthropod taxa. Female insects and arachnids generally have higher lipid contents than males, and larval holometabolous insects and juvenile arachnids have higher lipid contents than adults.
• Wolf, B. O., & Lease, H. M. (2010). Exoskeletal chitin scales isometrically with body size in terrestrial insects.. Journal of morphology, 271(6), 759-68. doi:10.1002/jmor.10835
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  The skeletal system of animals provides the support for a variety of activities and functions. For animals such as mammals, which have endoskeletons, research has shown that skeletal investment (mass) scales with body mass to the 1.1 power. In this study, we ask how exoskeletal investment in insects scales with body mass. We measured the body mass and mass of exoskeletal chitin of 551 adult terrestrial insects of 245 species, with dry masses ranging from 0.0001 to 2.41 g (0.0002-6.13 g wet mass) to assess the allometry of exoskeletal investment. Our results showed that exoskeletal chitin mass scales isometrically with dry body mass across the Insecta as M(chitin) = a M(dry) (b), where b = 1.03 +/- 0.04, indicating that both large and small terrestrial insects allocate a similar fraction of their body mass to chitin. This isometric chitin-scaling relationship was also evident at the taxonomic level of order, for all insect orders except Coleoptera. We additionally found that the relative exoskeletal chitin investment, indexed by the coefficient, a, varies with insect life history and phylogeny. Exoskeletal chitin mass tends to be proportionally less and to increase at a lower rate with mass in flying than in nonflying insects (M(flying insect chitin) = -0.56 x M(dry) (0.97); M(nonflying insect chitin) = -0.55 x M(dry) (1.03)), and to vary with insect order. Isometric scaling (b = 1) of insect exoskeletal chitin suggests that the exoskeleton in insects scales differently than support structures of most other organisms, which have a positive allometry (b > 1) (e.g., vertebrate endoskeleton, tree secondary tissue). The isometric pattern that we document here additionally suggests that exoskeletal investment may not be the primary limit on insect body size.
• Wolf, B. O., Mcdowell, N. G., Lease, H. M., Engel, S., & Corbett, A. H. (2009). The use of tunable diode laser absorption spectroscopy for rapid measurements of the delta13C of animal breath for physiological and ecological studies.. Rapid communications in mass spectrometry : RCM, 23(9), 1281-6. doi:10.1002/rcm.4004
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  In this study we introduce the use of tunable diode laser absorption spectroscopy (TDLAS) as a technique for making measurements of the delta13C of animal 'breath' in near real time. The carbon isotope ratios (delta13C) of breath CO2 trace the carbon source of the materials being metabolized, which can provide insight into the use of specific food resources, e.g. those derived from plants using C3 versus C4 or CAM photosynthetic pathways. For physiological studies, labeled substrates and breath analyses provide direct evidence of specific physiological (e.g. fermentative digestion) or enzymatic (e.g. sucrase activity) processes. Although potentially very informative, this approach has rarely been taken in animal physiological or ecological research. In this study we quantify the utilization of different plant resources (photosynthetic types--C3 or C4) in arthropod herbivores by measuring the delta13C of their 'breath' and comparing it with bulk tissue values. We show that breath delta13C values are highly correlated with bulk tissues and for insect herbivores reflect their dietary guild, in our case C3-specialists, C4-specialists, or generalists. TDLAS has a number of advantages that will make it an important tool for physiologists, ecologists and behaviorists: it is non-invasive, fast, very sensitive, accurate, works on animals of a wide range of body sizes, per-sample costs are small, and it is potentially field-deployable.
• Youberg, K. M., Smith, F. A., Raniszewski, A., Murray, I. W., Lease, H. M., Harding, L. E., & Crawford, D. L. (2009). A tale of two species: Extirpation and range expansion during the late Quaternary in an extreme environment. Global and Planetary Change, 65(3), 122-133. doi:10.1016/j.gloplacha.2008.10.015
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  Abstract Death Valley, California is today the hottest hyperarid area in the western Hemisphere with temperatures of 57 °C (134 °F) recorded. During the late Quaternary, pluvial Lake Manly covered much of the Valley and contributed to a much more moderate climate. The abrupt draining of Lake Manly in the mid-Holocene and coincident dramatic shifts in temperature and aridity exerted substantial selection pressure on organisms living in this area. Our research investigates the adaptive response of Neotoma (woodrats) to temperature change over the late Quaternary along a steep elevational and environmental gradient. By combining fieldwork, examination of museum specimens, and collection of paleomiddens, our project reconstructs the divergent evolutionary histories of animals from the valley floor and nearby mountain gradients (− 84 to > 3400 m). We report on recent paleomidden work investigating a transition zone in the Grapevine Mountains (Amargosa Range) for two species of woodrats differing significantly in size and habitat preferences: N. lepida, the desert woodrat, and N. cinerea, the bushy-tailed woodrat. Here, at the limits of these species' thermal and ecological thresholds, we demonstrate dramatic fluctuations in the range boundaries over the Holocene as climate shifted. Moreover, we find fundamental differences in the adaptive response of these two species related to the elevation of the site and local microclimate. Results indicate that although N. cinerea are currently extirpated in this area, they were ubiquitous throughout the late Pleistocene and into the middle Holocene. They adapted to climate shifts over this period by phenotypic changes in body mass, as has been demonstrated for other areas within their range; during colder episodes they were larger, and during warmer intervals, animals were smaller. Their presence may have been tied into a much more widespread historical distribution of juniper (Juniperus sp.); we document a downward displacement of approximately 1000 m relative to juniper's modern extent in the Amargosa Range. These results suggest a cooler and more mesic habitat association persisting for longer and at lower elevations than previously reported.
• Suedkamp, M. J., Snyder-conn, E., Morris, J. M., Meyer, J. S., Lease, H. M., Holt, R. A., Foott, J. S., & Clearwater, S. J. (2006). Survival of Lost River suckers (Deltistes luxatus) challenged with Flavobacterium columnare during exposure to sublethal ammonia concentrations at ph 9.5.. Archives of environmental contamination and toxicology, 50(2), 256-63. doi:10.1007/s00244-004-0194-x
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  The Lost River sucker (Deltistes luxatus) is a federally listed, endangered species inhabiting the hypereutrophic waters of Upper Klamath Lake in southern Oregon, USA. High pH (> or =10) and elevated ammonia concentrations (> or =1 mg NH(3)-N/L) often occur during blooms of cyanobacteria (Aphanizomenon flos-aquae) in the lake, with major fish kills sometimes following a mid- or late-summer "crash" of the cyanobacterial population. Previous histopathology analyses and bacterial sampling indicated that infections of the pathogenic bacterium Flavobacterium columnare might contribute to the fish kills. We hypothesized that prior exposure to adverse water quality conditions increases the susceptibility of Lost River suckers to F. columnare infections. To test this, we exposed juvenile Lost River suckers to four sublethal ammonia concentrations at pH 9.4 for 62 d. On day 31, fish in half of the aquaria were exposed to F. columnare. As expected, survival of the Lost River suckers decreased in aquaria inoculated with F. columnare. Ninety-four percent of the fish that died were infected by F. columnare in the gills, kidney, or skin, whereas none of the survivors or unexposed control fish was infected. However, contrary to our hypothesis, survival of the fish exposed to F. columnare increased significantly (p < 0.05) as unionized ammonia concentrations increased. Our results suggest that complex interactions can complicate prediction of the responses of fish to concurrent chemical stressors and bacterial pathogens.
• Wolf, B. O., Lease, H. M., & Harrison, J. F. (2006). Intraspecific variation in tracheal volume in the American locust, Schistocerca americana, measured by a new inert gas method.. The Journal of experimental biology, 209(Pt 17), 3476-83. doi:10.1242/jeb.02343
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  The volume of a tracheal system influences breath-holding capacity and provides an index of an insect's investment in its respiratory system. Here, we describe a new, generally applicable method to measure tracheal volume that enables repeatable determinations on live animals. Animals are isolated in a closed chamber of a known volume and equilibrated with a helium:oxygen gas mixture. The chamber is then rapidly flushed with a nitrogen:oxygen gas mixture to eliminate the helium surrounding the animal, and sealed. After a period of time sufficient to allow equilibration of helium between tracheal system and chamber air, a gas sample is taken from the chamber, and tracheal volumes are calculated from the helium content of the sample, using a gas chromatograph. We show that relative investment in the tracheal system increases with age/size in the grasshopper; tracheal volume scales with mass to the power 1.3. This increased proportional investment in the tracheal system provides a mechanistic basis for the enhanced respiratory capacity of older grasshoppers. Tracheal volumes decrease strongly as grasshoppers grow within an instar stage, explaining reduced safety margins for oxygen delivery. Finally, tracheal volumes are smaller in gravid females than males, probably due to compression of air sacs by eggs.
• Wolf, B. O., Meehan, T. D., & Lease, H. M. (2005). Negative indirect effects of an avian insectivore on the fruit set of an insect-pollinated herb. Oikos, 109(2), 297-304. doi:10.1111/j.0030-1299.2005.13578.x
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  Though an abundance of research has focused on direct interactions between birds and plants, relatively few studies have reported on indirect interactions. Of those reports, all have focused on positive indirect effects of birds on plants through predation of plant natural enemies. We conducted an observational study along the Middle Rio Grande in New Mexico to determine if avian aerial insectivores had a negative, indirect impact on insect-pollinated plants through predation of insect pollinators. We found considerable taxonomic overlap, at the order and family level, between insects visiting sweet clover (Melilotus officinalis) and those eaten by cliff swallows (Hirundo pyrrhonota). We found a significant negative relationship between proximity of sweet clover to cliff swallow breeding colonies and sweet clover fruit set during the cliff swallow nestling period. The apparent effect of cliff swallows was strongest within 200 m of breeding colonies (approximately 50% reduction in fruit set) and decreased nonlinearly to a distance of approximately 400 m. Finally, we found that the clover fruit set gradient disappeared after the nestling period, when chicks had fledged and the colony was abandoned.
• Meyer, J. S., Lease, H. M., Hansen, J. A., & Bergman, H. L. (2003). Structural changes in gills of Lost River suckers exposed to elevated pH and ammonia concentrations.. Comparative biochemistry and physiology. Toxicology & pharmacology : CBP, 134(4), 491-500. doi:10.1016/s1532-0456(03)00044-9
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  The Lost River sucker (Deltistes luxatus) is a federally listed, endangered fish that occurs primarily in Upper Klamath Lake-a hypereutrophic lake in southern Oregon, USA. A decline of the sucker population in the lake over the past few decades has been partly attributed to adverse water quality conditions, including elevated pH and ammonia concentrations that occur during summer cyanobacterial blooms. We quantitatively analyzed structural changes in gills of larval Lost River suckers after they were exposed to elevated pH and ammonia concentrations for 30 d. Exposure to pH as high as 10 caused no observed structural changes. However, lamellar thickness and O(2) diffusion distance increased significantly (P

Presentations

• Lease, H. M. (2018, July). Differences in habitat selection in co-occurring blue (Connochaetes taurinus) and black wildebeest (C. gnou) based on thermoregulatory differences. The Society for Experimental Biology. Florence: Company of Biologists / Journal of Experimental Biology.