Thesis (M.S.)--Western Washington University, 2010. / Includes bibliographical references (leaves 69-75). Also issued online.

Thesis (Ph. D.)--University of Nevada, Reno, 2006. / "May 2006." Includes bibliographical references. Online version available on the World Wide Web.

The Western Fence Lizard (Sceloporus occidentalis) is a major host of juvenile stages of the Western Black-legged Tick (Ixodes pacificus), which is the vector for the Lyme disease causative spirochete bacterium Borrelia burgdorferi in the western United States. Because S. occidentalis is reservoir incompetent and capable of eliminating spirochetes from infected ticks, it has been implicated as a major factor in the ecology of Lyme disease in the West. Although complement proteins in lizard blood have been established as the borreliacidal factor, no studies have examined intraspecific variability in host lizard borreliacidal capacity. In Chapter 1 of this thesis, we introduce the complexity of the Borrelia burgdorferi transmission cycle and it’s implications for transmission risk. In Chapter 2 we tested the hypothesis that host lizard physiological condition impacts their borreliacidal capacity. Blood plasma of lizards in varying physiological conditions was challenged against cultured B. burgdorferi, and the complement-mediated inactivation of spirochetes was quantified. Adult lizards had higher bactericidal activity than first-year juveniles, suggesting that complement-mediated inactivation develops with maturity and/or exposure to spirochete antigens. Also, bactericidal activity was positively associated with lizard tick load and body condition. Adult lizard sex did not significantly affect spirochete mortality. Lizards from an inland site with little exposure to ticks had higher bactericidal activity than lizards from a coastal population that is heavily parasitized by ticks.

Chapter 1: Animals can respond to extreme climate by behaviorally avoiding it, or by physiologically coping with it. We understand behavioral thermoregulation and physiological thermal tolerances, but water balance has largely been neglected. Climate change includes both global warming and changes in precipitation regimes, so improving our understanding of organismal water balance is increasingly urgent. We assessed the hydric physiology of endangered Blunt-nosed Leopard Lizards (Gambelia sila) by measuring cutaneous evaporative water loss (CEWL), plasma osmolality, body mass, and body condition throughout their active season. On average, G. sila had low CEWL that is likely desert-adaptive, and high plasma osmolality that is indicative of dehydration. Given that our study was in a drought year, it is reasonable to believe that every lizard measured was dehydrated to a degree. We hypothesized that throughout the G. sila active season, as their habitat got hotter and drier, G. sila would become increasingly dehydrated and watertight. Instead, CEWL and plasma osmolality showed minimal change for females and nonlinear change for males, which we hypothesize is connected to sex-specific reproductive behaviors and changes in food availability. We also measured thermoregulation and microhabitat use, expecting that more hydrated lizards would have higher body temperature, better thermoregulatory accuracy, and spend more time aboveground. However, we found no effect of CEWL, plasma osmolality, body mass, or body condition on these thermal and behavioral metrics. We posit either that G. sila tolerate dehydration to maintain activity during their brief active season, or that because every lizard was dehydrated due to the drought, they all experienced equally constrained thermoregulation and microhabitat use. Finally, G. sila spend considerable time underground in burrows, and we believe burrows serve as essential hydric, not only thermal, refugia. Our findings suggest that these lizards might benefit from artificial humid refugia and supplemental hydration, especially during drought. Chapter 2: Testing acclimation plasticity informs our understanding of functional biodiversity and applies to conservation management amidst our rapidly changing climate. While there is a wealth of research on the plasticity of thermal and hydric physiology in response to temperature acclimation, there is a comparative gap for research on acclimation to different hydric regimes, as well as the interaction between water and temperature. We sought to fill this gap by acclimating Western Fence Lizards (Sceloporus occidentalis) to experimental climate conditions (crossed design of Hot or Cool, Dry or Humid) for eight days, and measuring cutaneous evaporative water loss (CEWL), plasma osmolality, hematocrit, and body condition before and after acclimation under common conditions. CEWL changed plastically in response to the different climates, with lizards acclimated to Hot Humid conditions experiencing the greatest increase in CEWL. Change in CEWL among individuals was negatively related to treatment vapor pressure deficit. Plasma osmolality, hematocrit, and body condition all showed greater changes in response to temperature than to humidity or vapor pressure deficit. CEWL and plasma osmolality were positively related across treatment groups before acclimation and within treatment groups after acclimation, but the two variables showed different responses to acclimation, suggesting that they are interrelated but governed by different mechanisms. This study is among just a small number of studies that assess more than one metric of hydric physiology and that test the interactive effects of temperature and humidity. Such measurements will be essential for predictive models of activity and survival for animals under climate change.

Understanding the effects of natural variation in environmental temperature on organisms and how those organisms evolve to live in different thermal environments is a central tenet of evolutionary physiology. Phenotypic differences among populations are the result of local adaptation, innate genetic differences between populations, and phenotypic plasticity, differential responses to the environment. Although not mutually exclusive, distinguishing between these paradigms can help illuminate species boundaries resulting from thermal limitations in physiology. For my dissertation, I examined geographic variation in measures of thermal physiology of the western fence lizard, Sceloporus occidentalis to understand the relative role of adaptation and acclimation in determining the thermal biology of populations of this species living in different thermal environments. To achieve this goal I measured three indices of physiological function; body temperature, thermal tolerance and heat shock protein (Hsp70) abundance, across geographic and seasonal variation in temperature. Furthermore, I examined variation in sprint speed performance before and after heat stress and its relationship to Hsp70 to determine if stress protein expression is a reliable indicator of whole organism physiological stress. I found that geographic location can have a major effect on thermal physiology and performance in S. occidentalis in that thermal tolerance, Hsp70, and sprint speed varied with site and season with warmer southern sites typically more heat adapted than cooler northern sites. I also found a trade off in thermal tolerance suggesting that specialization to temperature was occurring in these lizards. Finally, lizards with increased Hsp70 were typically slower after heat stress indicating that Hsp70 is a reliable indicator of organism stress. Despite these findings, there was no difference in body temperature among sites and seasonal patterns in thermal tolerance suggest that during certain times of the year plastic responses to temperature may mask adaptive differences. Here, I argue that temperature differences between sites has resulted in temperature adaptation at these sites, but that plastic responses to seasonal variation in temperature can become more important during certain times of the year. Although these relationships have been thoroughly studied in invertebrate organisms, further research should examine whether these patterns exist in other vertebrate ectotherm species.

The thermal environment exerts a strong influence on many aspectsof squamate life history. Environmental temperatures constrain daily activity time, fecundity, growth rate, and also influences hatchling phenotype. Cold nest temperatures can slow the development of eggs deposited in the soil, cause developmental abnormalities or result in mortality of embryos.