A chromosomal inversion may facilitate adaptation despite periodic gene flow in a freshwater fish

Abstract

Genomic architecture, such as chromosomal inversions, may play an important role in facilitating adaptation despite opportunities for gene flow. One system where chromosomal inversions may be important for eco-evolutionary dynamics are in freshwater fish, which often live in heterogenous environments characterized by varying levels of connectivity and varying opportunities for gene flow. In the present study, reduced representation sequencing was used to study possible adaptation in n=345 walleye (Sander vitreus) from three North American waterbodies: Cedar Bluff Reservoir (Kansas, USA), Lake Manitoba (Manitoba, Canada), and Lake Winnipeg (Manitoba, Canada). Haplotype and outlier-based tests revealed a putative chromosomal inversion that contained three expressed genes and was nearly fixed for alternate genotypes in each Canadian lake. These patterns exist despite several opportunities for gene flow between these proximate Canadian lakes, suggesting that the inversion may be important for facilitating adaptative divergence between the two lakes despite gene flow. Our study illuminates the importance of genomic architecture for facilitating local adaptation in freshwater fish and provides additional evidence that inversions may facilitate local adaptation in many organisms that inhabit connected but heterogenous environments.