Meeting Abstract
Divergent selection and limited gene flow across varying environments may lead to population differentiation at small spatial scales. On the California Channel Islands, song sparrows (Melospiza melodia graminea) occupy a steep climate gradient and exhibit low dispersal. Population genomic results suggest selection drives observed bill variation with larger bills found on hotter islands, consistent with hypotheses stating the avian bill is a thermoregulatory tool. However, the bill represents only a small proportion of the body capable of heat loss. Furthermore, how the relationship between thermogenesis, thermal conductance, and morphology varies between populations remains unknown. Here, we examine the relationship between (1) climate and feather microstructure and (2) climate and thermal physiology. Specifically, we quantified differences in breast contour feathers between island and mainland sparrows (M. m. heermanni) to infer insulatory ability. We coupled this with respirometry experiments to determine whether populations exhibit differences in metabolic rates and thermal limits. We found no significant difference among regions in physiological traits. Yet, we identified a significant difference in the proportion of the feather that was plumulaceous and evidence for greater barb density in birds from colder islands. Plumage results suggest birds on colder islands have better insulation, likely a plastic response to climate based on work in other species. Together, this suggests that populations may cope with climatic challenges by first modifying morphological characteristics before altering complex, physiological traits.
