Here be dragons: Functional analyses of thermal adaptation and biogeography of reptiles in a changing world
Environments around the world are changing rapidly and a major challenge for modern biologists is to understand how these changes affect organisms, communities, and ecosystems. Ideally, we would like to predict which taxa/populations are likely to remain stable, increase, or decline in response to predicted environmental perturbations. This information will allow us to create informed management plans and will provide insight into the ecological and evolutionary processes that shape biodiversity. For my Ph.D. dissertation, I examined factors that mediate the responses of reptile populations to rapid changes in the thermal environment, explored the ability of these factors to shift through phenotypic plasticity and evolution, and examined the power of a phenotypically plastic behavioral response to buffer populations from thermal environmental change.
In Chapters 2-4, I explored the evolutionary history and physiology of alligator lizards (Elgaria coerulea, E. multicarinata, and E. panamintina, family Anguidae) to identify mechanisms that mediate their responses to changing thermal environments. First, I integrated morphological data and species distribution modeling with prior molecular data to examine alligator lizard taxonomy. My results support the species status of E. panamintina and the existence of two cryptic taxa within E. multicarinata>. Next, I examined the thermal physiology of confirmed alligator lizard taxa and explored the biogeographical implications of their thermal physiology. Adult alligator lizards are active at virtually identical body temperatures even though species occur in very different thermal environments, suggesting average differences in environmental temperature are not limiting. To examine whether extreme temperatures might be more limiting, I examined the effects of extreme temperatures on the physiological stress response of alligator lizards. My results suggest that the thermal-stress response in alligator lizards is species specific and might be important for limiting alligator lizard biogeography. However, adults might not be the most thermally sensitive life-history stage. Thus, I also examined the effects of temperature during alligator lizard development and compared embryonic and adult thermal physiologies. My results suggest that the thermal physiology of alligator lizards changes across their ontogeny and embryonic thermal tolerances are more limiting than adult thermal tolerances. Together, my results suggest that relatively extreme thermal environments and the developmental thermal environment will have the greatest influence on how alligator lizards respond to changes in the thermal environment.
As environments change, many species may be able to respond adaptively through phenotypic plasticity, thereby countering any negative consequences of shifting environments. For example, the most common biotic response to ongoing global climate change is a plastic shift in spring phenology. While altered spring phenology is viewed as an adaptive response to changing thermal environments, this issue has not been examined directly. To test this hypothesis, in Chapter 6, I constructed a mechanistic model examining the power of shifting spring phenology to buffer populations from climate change, and examined this model using data on painted turtles (Chrysemys picta, family Emydidae), a species with temperature-dependent sex determination. Somewhat surprisingly, the model suggested that advancing phenology is a poor buffering mechanism, and only effectively counters the negative consequences of < 1.0 Â°C increase in environmental temperature.
In combination, my dissertation explores the diverse processes that mediate responses of reptiles to rapid changes in thermal environments such as those predicted to occur as a result of global climate change. This information is necessary to better understand effects of major environmental changes on the ecology and evolution of species as well as for making accurate predictions for conservation/management.