• Physiological Responses to Temperature in the Lizard, Sceloporus Undulatus

      Ehrenberger, Joseph C. (2010-07-20)
      Temperature affects all organisms differently. Physiological processes, such as metabolism, interact with temperature to determine a minimal rate of energy loss. Physiological limits, such as heat and cold tolerances, likely constrain the activity and survival of organisms. Ultimately, these physiological processes and limits determine a species‘ geographical distribution. Through experiments, I sought to understand specifically how temperature affects the physiology of the lizard Sceloporus undulatus. This species is a model organism to answer such questions, as it is geographically widespread species and well-described phylogenetically. In the first experiment, I compared standard metabolic rates of lizards from three locales and interpreted these rates in the context of the metabolic theory of ecology—a set of models that describes the effects of body mass and body temperature on metabolic rate. My findings indicate that metabolic rate increases with body size, but that the exact nature of this relationship depends on temperature; this result contrasts a major assumption of the metabolic theory of ecology, which stresses the need to evaluate this theory through by examining intraspecific variation. In my second experiment, I measured the preferred body temperatures and critical thermal limits of S. undulatus. Existing theory indicates that physiological traits associated with temperature may be evolutionary static or labile. By measuring these traits from seven populations, which cover the majority of this species‘ range, I have provided one of the most comprehensive comparisons of thermal physiology in a single biological species. My results are consistent with the static view of thermal physiology, suggesting that thermal physiology has not adapted to local conditions in this species.