Meeting Abstract
Strong divergent selection and limited gene flow across varying environments should lead to adaptive population differentiation. Archipelagos are unique evolutionary models to understand the role of divergent selection on phenotypic differences given the relative isolation of island populations. On the California Channel Islands, song sparrows (Melospiza melodia graminea) are found along a strong climate gradient and exhibit low dispersal across islands. Divergent selection due to climate has been linked to variation in bill size, a tool used to radiate heat. However, the bill represents only a small proportion of a bird’s surface area that can lose heat, and denser plumage may be an effective means of reducing heat dissipation in cooler environments. Here, we test the relationship between climate and feather micro-structure. Specifically, we looked at breast contour feathers from birds on islands representing different climates and compared characteristics of the plumulaceous and pennaceous sections—the plumulaceous section being most closely associated with insulation ability. We find significant differences between islands in the proportion of the feather that is plumulaceous, as well as evidence for greater barb density in birds from colder islands. Both higher barb density and a higher proportion of plumulaceous feather area provide better insulation, and this suggests selection due to climate differences may facilitate these population differences.
