METABOLIC ADAPTATIONS TO TEMPERATURE IN LIZARDS OF THE GENUS SCELOPORUS FROM DIFFERENT LATITUDES (WASHINGTON, CALIFORNIA, COSTA RICA)

Thermal acclimation is considered an important short-term, physiological adaptation of ectotherms to adjust to change in environmental temperature. Various acclimation responses to temperature are described as ecologically significant; however, these adaptive hypotheses are largely untested. This study uses an integrative approach to evaluate these hypotheses by examining patterns of thermal acclimation of resting metabolism in different thermal environments. Specifically, latitudinally separate populations of lizards (Sceloporus occidentalis from Washington and southern California and S. variabilis from Costa Rica) are compared to test predictions of acclimation responses in relation to thermal variability. The magnitude of acclimation should increase with latitude, and the direction of the response (increase or decrease metabolic rate after cold exposure) should depend on whether lizards are active or hibernate in cool seasons.;The third chapter establishes that populations from temperate-zone and tropical latitudes differ in acclimation response after common exposure to cold conditions in the laboratory. As expected, tropical lizards from Costa Rica showed no acclimation at 35 C, 16 C, and 10 C, California lizards increased metabolic rate, and Washington lizards decreased metabolic rate. Strong experimental protocols and statistical techniques enhanced the power of these analyses. This study examines acclimation within individuals and tests for repeatability of variation in metabolic rate among individuals across temperature and time. Consequently, this research supports the theory that acclimation responses depend on adaptation at different latitudes, and also demonstrates that acclimation responses are affected by other factors such as experimental regimes.;The first chapter documents daily and seasonal changes in body and environmental temperatures to establish that thermal variability experienced by lizards increases with latitude. In the second chapter, seasonal changes in metabolic rate at 35 C, 16 C, and 10 C of the temperate-zone populations are quantified to examine latitudinal differences in pattern of acclimatization in nature. Lizards from Washington had the lowest metabolic rates in winter during hibernation. California lizards, which are active during winter, had winter rates that were similar to those of mid-summer and lowest rates in late-summer at the hottest time of the year.