Despite decades of work, our understanding of the distribution of fitness effects of segregating genetic variants in natural populations remains largely incomplete. One form of selection that can maintain genetic variation is spatially varying selection, such as that leading to latitudinal clines. While the introduction of population genomic approaches to understanding spatially varying selection has generated much excitement, little successful effort has been devoted to moving beyond genome scans for selection to experimental analysis of the relevant biology and the development of experimentally motivated hypotheses regarding the agents of selection.
Solar UVB incidence is negatively correlated with latitude and an important agent of DNA damage in nature. Motivated by population genomic results, we investigated whether clinal variation in UVB incidence has led to genetic differences in the DNA damage response of D. melanogaster populations. Using a combination of population genomics, transcriptomics, and organismal phenotypic analysis, we show that genetic variation in the DNA damage response in D. melanogaster is maintained by spatially varying selection due to latitudinal variation in solar UVB incidence.