P1.47 Wednesday, Jan. 4 The relationship between testosterone and aggressive phenotype in male song sparrows (Melospiza melodia ) SEWALL, K. B.*; NOWICKI, S.; Duke University; Duke University firstname.lastname@example.org
Male songbirds face a trade-off between providing parental care and seeking mates. Individuals may resolve this trade-off differently, potentially generating equally adaptive paternal and aggressive male behavioral phenotypes in a population. Even in the absence of distinct phenotypes, male songbirds often vary in their behavioral strategy, as seen for example in the persistent individual differences in levels of territorial aggression described in male song sparrows (Melospiza melodia ). Consistent individual differences in aggression could be explained by individual differences in circulating levels of testosterone, or by brain mechanisms such as arginine vasotocin (AVT) levels or aromatase activity. To determine how plasma testosterone might contribute to persistent differences in aggressiveness, we measured male response to standardized field simulated territory intrusions (STIs). We captured males immediately after STI and took plasma samples within 3 min. and then again after males had been held in the lab for 2 weeks and were habituated to captivity. We quantified plasma testosterone levels using enzyme immunoassay (Assay Designs). We did not find that either base-line or STI-induced testosterone levels correlated reliably with an established measure of aggressive phenotype, the mean approach to the decoy mount and speaker. However, latency to finally approach the decoy and be captured in response to field playback was negatively correlated with STI-induced testosterone. Fully characterizing the endocrine and neuroendocrine architecture of aggressive phenotypes will require future studies examining testosterone levels in response to GnRH challenge and neuropeptide and aromatase expression in the brain.