This project proposes to examine the involvement of thyroid hormones in regulating aerobic energetic capacities to sustain locomotor activity in reptiles. As endothermy evolved independently in mammals and birds along essentially parallel lines of reptilian ancestry, these studies on extent reptiles may provide insight into non-thermoregulatory roles of thyroid hormones in the ancestral conditions that led to modern endotherms. Three complementary lines of research will be conducted. Firstly, natural seasonal cycles in total and free levels of thyroid hormones and correlated changes in physiological and behavioral factors will be analyzed to provide the interpretational framework for experimental work. Secondly, laboratory experiments will employ new methods to induce physiological alterations in levels of thyroid hormones in regulating particular processes. Thirdly, field experiments will be done to regulate levels of thyroid hormones in field-active lizards and to test the involvement of seasonal hormone cycles in regulating particular processes. The research is expected to yield new information on the regulation by thyroid hormones of physiological processes that support activity and may help to clarify the adaptive significance of these processes in relation to natural activity.
