Endothermy provides substantial freedom from the vagaries of the environment, but comes at considerable energetic costs. While the advantages of effective endothermy have been "explained" by various models, including the thermoregulatory model, the aerobic capacity model, and the reproductive model, very few empirical studies have been conducted. Furthermore, the initial driving forces that provided selective advantages of limited endothermic ability are not only untested but also are rarely explained by the proposed models. The reproductive model is unique in providing selective advantages to a stepwise progression in endothermic ability. While novel in this respect, the reproductive model also remains untested. It is not surprising that empirical tests of the models for the evolution of endothermy are rare since few extant organisms provide an opportunity to assess the selective advantages of limited endothermy. However, this project will capitalize on the unique egg brooding characteristics of pythons, where all species brood their eggs, but only some species have evolved limited facultative endothermy. This study will use a combination of experiments. First, a comparative assessment of endothermic capability among pythons will be conducted in order to evaluate the effect that various species traits (e.g., phylogenetic relationships, body size, climate) have on endothermic capability. Second, the investigators will construct artificial variably-endothermic snake models to test the hypothesis that stepwise increments in endothermic capability lead to stepwise control of the embryonic thermal environment. Lastly, eggs will be incubated at various thermal environments to assess the impact that thermal regulation of the embryonic environment has on offspring quality. Combined, these experiments will provide a rare empirical test of the reproductive model for the evolution of endothermy. Beyond its strong scientific merit, this project has a broader impact in that it will provide an exceptional educational opportunity in requiring the direct participation of both graduate and undergraduate researchers. The nature of this project will emphasize to students the importance of using physiological approaches to empirically test evolutionary models. Additionally, the broader impact of this study will extend beyond academia into the general public through media coverage, documentaries, and the creation of a public outreach component to the laboratory's web site.
