Meeting Abstract

103.4  Tuesday, Jan. 7 09:00  Advanced reproductive phenology of an urban bird is not mirrored in the underlying reproductive physiology DAVIES, S*; DEVICHE, P; Arizona State University; Arizona State University Scott.Davies@asu.edu

For seasonally breeding animals, the decision of when to begin breeding each year has considerable effects on fitness. Birds cycle between periods of breeding activity and inactivity, which is associated with large changes in reproductive physiology and morphology. These changes require time, so birds begin to develop their reproductive system well before environmental conditions are optimal for breeding. To do this, they use environmental cues that predict conditions favorable for reproduction. Environmental conditions in urban areas of Phoenix differ from those of outlying desert areas in many respects. We hypothesized that environmental differences are associated with differences in the timing of development of reproductive morphology and physiology between urban and desert birds. To test this hypothesis, we compared the development of gonads and cloacal protuberances (a secondary sexual characteristic in male birds) between urban and desert adult male Abert’s Towhees, Melozone aberti. To investigate the mechanism controlling reproductive development, we also measured plasma concentrations of the key reproductive hormone testosterone, which is thought to promote development of the cloacal protuberance and expression of reproductive behavior. Compared to desert conspecifics, development of reproductive morphology was advanced in urban birds. The vernal increase in testosterone, however, was similar in urban and desert birds. The reason for the discrepancy between development of reproductive morphology and physiology is unclear. It may reflect the lability of plasma hormone levels over short periods and/or it may suggest that physiological processes other than or in addition to reproductive hormones transduce environmental information to reproductive development.