This project investigates the development of endothermy - the ability to maintain a high, internally regulated, and constant body temperature ? in birds that span a range of functional maturity at hatching. All vertebrate embryos are ectothermic, for which metabolic rate and body temperature decrease as ambient temperature decreases. The "thermostat" and cellular "furnace" of ectothermic stages are unable to maintain a high constant body temperature without an external heat source. Endothermy develops in birds as they mature from an embryo to a free-living hatchling. An endothermic phenotype matures rapidly in precocial birds that hatch with feathers and quickly develop a high basal metabolic rate. In contrast, the endothermic phenotype develops gradually in altricial birds that hatch featherless, with little motor control, and limited metabolic capacity. The metabolic transition from ectothermy to endothermy has been well documented at the whole animal level, but the biochemical and cellular basis governing this transition remain unclear. Research proposed here will elucidate the physiological ontogeny of endothermy in birds by 1) correlating organism level physiology with cellular level physiology of ATP production and consumption in tissues serving as the cellular furnace and 2) manipulating levels of thyroid hormones to examine their role in regulating this metabolic conversion. The research questions will be addressed using a comparative approach that focuses on precocial and altricial species that develop endothermy at different rates post-hatching and compares them with out-group species that remain ectotherms throughout life. Experimentally, thyroid hormone levels will be manipulated in precocial and altricial species to determine its regulatory role in this energetic metamorphosis. Elucidating the developmental trajectories of whole animal metabolism, mitochondria function, and cellular processes and the role of thyroid hormones associated with attaining endothermy will provide a major new interpretation of important developmental events, leading to a better understanding of the evolution of endothermy. This project features collaboration of labs at University of North Texas, Kalamazoo College, and North Dakota State University. The research project will include educational and research training for graduate, undergraduate, and high school students.
