TY - JOUR T1 - Ancient genomic variation underlies recent and repeated ecological adaptation JF - bioRxiv DO - 10.1101/167981 SP - 167981 AU - Thomas C. Nelson AU - William A. Cresko Y1 - 2017/01/01 UR - http://biorxiv.org/content/early/2017/07/25/167981.abstract N2 - Adaptation in the wild often involves the use of standing genetic variation (SGV), allowing rapid responses to selection on ecological timescales. Despite increasing documentation of evolutionarily important SGV in natural populations, we still know little about how the genetic and genomic structure and molecular evolutionary history of SGV relate to adaptation. Here, we address this knowledge gap using the threespine stickleback fish (Gasterosteus aculeatus) as a model. We demonstrate that adaptive genetic variation is structured genome-wide into distinct marine and freshwater haplogroups. This divergent variation averages six million years old, nearly twice the genome-wide average, but has been evolving over the 15-million-year history of the species. Divergent marine and freshwater genomes maintain regions of ancient ancestry that include multiple chromosomal inversions and extensive linked variation. These discoveries about ancient SGV demonstrate the intertwined nature of selection on ecological timescales and genome evolution over geological timescales. ER -