DISSERTATION RESEARCH: HORMONAL REGULATION OF IMMUNE FUNCTION IN SEASONALLY-BREEDING BIRDS
Noah T. Owen-Ashley & John C. Wingfield
University of Washington, Seattle
The steroid hormone testosterone (T) is thought to have bidirectional effects on fitness in many vertebrates. T is important in orchestrating reproductive and aggressive behavior in males, and promoting the development of many secondary sex characters important for female choice. On the other hand, high levels of T are thought to suppress immune function. Many studies in birds have found that T suppresses some component(s) of the immune system, but it is not known if this mechanism occurs through direct or indirect pathways. The main goal of this research is to understand the contributions of these pathways in regulating T-induced immunosuppression in the Northwestern Song Sparrow (Melospiza melodia morphna) and the White-crowned Sparrow (Zonotrichia leucophrys). Experimental elevation of T in many bird species alters the levels of other hormones, such as corticosterone and estradiol, which also regulate immunity. Therefore, avian immune function may be altered through these intermediary hormones, rather than by testosterone directly. A suite of experiments will be conducted on both species involving the use of hormone implants and/or pharmacological blockers to tease apart these direct and indirect effects on physiological and behavioral immune function. These studies will provide new insights into hormonal regulation of immunity in seasonally-breeding birds, and reconcile existing theories which assume a direct role of T in regulating a tradeoff between immunocompetence and reproductive success in male vertebrates.
