47.3 Thursday, Jan. 5 Population-level Variation in Endogenous Testosterone, Mating and Paternal Effort Across an Elevation Gradient KAISER, S/A*; WEBSTER, M/S; SILLETT, T/S; Cornell University, Ithaca; Cornell University, Ithaca; Smithsonian Migratory Bird Center, Washington, DC email@example.com
Climate change is causing temporal shifts in the environmental cues migratory birds and other animals use to synchronize breeding events with optimal foraging conditions, and these shifts potentially could have drastic consequences. Seasonal changes in circulating hormone levels can modulate avian reproductive behaviors that directly influence fitness, but we know surprisingly little about the environmental cues that signal the underlying endocrine mechanisms generating behavioral variation, nor how these will respond to changing conditions. At the population level, we examined the linkage between endogenous testosterone and investment in mating and parental behaviors by Black-throated Blue Warbler males breeding along a 600 m elevation gradient in New Hampshire. Birds nesting at high elevation experience cooler temperatures than those nesting at low elevation, however the caterpillar biomass is two times greater at high elevation. We found that testosterone levels were elevated during the fertile period compared to the parental period and greatest during the fertile period at mid and high elevations where males invested more effort in extra-pair mating and less in paternal care. These results suggest a testosterone-mediated trade-off between mating and paternal effort influenced by differences in environment across the elevation gradient. However, endogenous testosterone levels were variable among males within the same nesting stage across elevations. Therefore, an important next step to understand the extent to which plasticity in the hormone-regulated reproductive behaviors is adaptive is to examine these relationships at the level of the individual experiencing different environmental extremes.