Is structural variation necessary to create islands of divergence in
moderate gene flow species? A case study in sockeye salmon
Local adaptation is often facilitated by loci clustered in relatively
few regions of the genome, termed genomic islands of divergence.
However, the mechanisms that create, mold, and maintain these islands
are poorly understood. Here, we use sockeye salmon as a model species to
investigate the mechanisms responsible for creating islands of
divergence linked to adaptive variation. Previous research suggests that
multiple islands are involved in adaptive radiation of sockeye salmon.
However, these studies were based on low-density genomic methods that
genotyped tens to thousands of loci, making it difficult to elucidate
the mechanisms responsible for islands. We used whole genome
resequencing to genotype millions of loci to investigate these
mechanisms. We discovered 64 islands, 16 of which were shared between
two isolated populations; these 16 islands were clustered in four
genomic regions. Characterization of the shared regions suggested that
three of four were likely created by chromosomal inversions, while the
other was created by processes not involving structural variation.
Additionally, all four regions were relatively small (< 600
kb), suggesting inversions and other low recombination regions do not
have to span megabases to be important for adaptive divergence. In sum,
our study demonstrates that heterogeneous selection can lead to a mosaic
of islands created by different mechanisms within the same genome.
Future studies should continue to investigate how gene flow, selection,
and the architecture of genetic traits interact to influence the genomic
landscape of adaptive divergence.