Evidence of selection in sympatry between two closely related species of
rockfish
Abstract
Ecological or reproductive barriers can maintain species by preventing
introgression in closely related taxa when their distributions overlap.
In sympatry, sister-taxa may have greater genetic divergence than
comparing the sister-taxa in allopatric parts of their range. When
analyzing populations within a species, this may translate to greater
genetic divergence between sympatry and allopatry. This genetic
differentiation can be caused by either genetic drift or natural
selection, depending on the evolutionary history of secondary contact.
To identify a selective process, it is critical to find genes
responsible for maintaining species barriers in sympatry. Here, we
examined the role of natural selection in genetic differentiation within
two recently diverged rockfish species, Sebastes diaconus and
Sebastes mystinus. These species overlap along over 400 km of
coastline in the eastern Pacific, with no evidence of hybridization. We
found evidence of geographic genetic differentiation across a large span
of the S. diaconus range, but not within S. mystinus. For
both species, we identified outlier loci associated with regions of the
genome under directional selection in allopatric versus sympatric
populations. We also found signals of directional selection in shared
genomic regions of both species, suggesting the evolutionary process of
reinforcement maintained species boundaries once the two species were in
secondary contact.