Off-campus UMass Amherst users: To download dissertations, please use the following link to log into our proxy server with your UMass Amherst user name and password.

Non-UMass Amherst users, please click the view more button below to purchase a copy of this dissertation from Proquest.

(Some titles may also be available free of charge in our Open Access Dissertation Collection, so please check there first.)

Functional consequences of acute temperature stress in the western fence lizard, Sceloporus occidentalis

David Michael McMillan, University of Massachusetts Amherst

Abstract

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.

Subject Area

Ecology|Physiology

Recommended Citation

McMillan, David Michael, "Functional consequences of acute temperature stress in the western fence lizard, Sceloporus occidentalis" (2010). Doctoral Dissertations Available from Proquest. AAI3397733.
https://scholarworks.umass.edu/dissertations/AAI3397733

Share

COinS