Meeting Abstract

14.4  Tuesday, Jan. 4  The effect of testosterone on molt in House Finches (Carpodacus mexicanus) BRAZEAL, K.R.*; HAHN, T.P.; Univ. of California, Davis; Univ. of California, Davis krbrazeal@ucdavis.edu

In seasonally-breeding birds, the timing of the transition between breeding and molt represents an important life-history trade-off between the benefits of extended current reproduction and the costs of delayed molt, which may reduce long-term survival. Despite its importance, little is known about the endocrine control mechanisms responsible for orchestrating the breeding-molt transition. Past studies have established that high levels of sex steroids (e.g. estradiol and testosterone associated with breeding) can delay the onset of molt. The details of how sex steroids regulate the timing of this transition remain unclear. In this study male house finches were given testosterone implants of one of three different doses prior to the start of molt and the effect on molt onset and progression was quantified. Control males were given empty implants. Testosterone-implants delayed onset of molt compared with controls, but not in a dose-dependent way (at least not at the doses we used). There was large variation in molt onset date among individuals in each testosterone dose group. It remains to be seen whether testosterone has dose-dependent effects on timing of completion of molt. Our finding contrasts with a similar study of molt in starlings which showed a strong dose-dependent response to testosterone. This suggests that species may vary in the mechanisms that control the transition from breeding to molt. Further comparative work will elucidate whether such mechanistic differences can help to explain species differences in annual schedules observed in the wild.