Variation in Resource Environment Drives Adaptive Divergence inDrosophila melanogaster

Abstract

Natural populations often experience heterogeneity in the quality and abundance of environmentally acquired resources across both space and time, and this variation can influence population demographics and evolutionary dynamics. In this study, we directly manipulate resource quality in replicate populations of Drosophila melanogaster cultured in experimental mesocosms in the field. We found no significant effect of resource variability on demographic patterns. Furthermore, while resource variation altered the patterns of phenotypic and genomic evolution, this effect is secondary to population responses to seasonally fluctuating selective pressures. Seasonal adaptation was observed for all traits assayed and was highly polygenic; in contrast, adaptation to the resource environment was trait-specific and exhibited an oligogenic architecture. This illustrates the capacity of populations to adapt to an additional axis of variation (resource availability) without hindering the adaptive response to seasonal change. This ability for populations to simultaneously track and respond to variations in multiple environmental factors likely drives divergent or fluctuating selection, contributing to the maintenance of genetic and phenotypic variation in natural populations.