Hormones simultaneously mediate numerous traits of plants and animals thus coordinating expression of size, physiology and behavior. When environments change or new environments are colonized, this common control of traits by hormones may or may not facilitate adaptation to the altered environment, depending on the details of hormonal control. In vertebrate animals, the hormone testosterone (T) has particular importance for traits related to reproduction, such as ornamentation and aggression. The common control of traits by T may facilitate adaptation by preserving favorable combinations (e.g., aggression coupled with ornamentation to simultaneously deter rivals and attract mates) or delay adaptation if control of a potentially beneficial trait is linked by the hormone to another trait that would be detrimental. This interplay has important implications for species evolution and response to climate change, yet we know surprisingly little about its actual nature. This project will support field and laboratory research to address whether relationships between T and various behavioral and morphological traits observed in one sub-species of a songbird, the dark-eyed junco, can be used to predict the same relationships in another subspecies that lives in a very different environment. The project will also examine the underlying physiological mechanisms that may contribute to potential differences in these relationships, asking whether they vary among individuals and subspecies. Specifically, hormone manipulations and neural studies with captive birds will examine hormonal cascades that trigger T release, as well as hormone receptors that affect T's influence on traits. Consistent co-variation between T, traits, and physiological mechanisms across subspecies will suggest that hormone systems evolve as a unit. Alternatively, absence of similarity across populations will suggest high potential for independent evolution, allowing hormone systems to diverge more freely or less consistently. The research will provide numerous opportunities for effective mentorship of diverse undergraduates, and the findings are expected to contribute to an understanding of hormone system evolution.
