Inter-island local adaptation in the Galápagos Archipelago: genomics of the Galápagos blue-banded goby, Lythrypnus gilberti

Abstract

The Galápagos Archipelago is a place where terrestrial adaptive radiations of finches, mockingbirds, and tortoises have been studied extensively. In contrast, little is known about the potential for marine species to diverge among islands. The overall degradation of coral reefs in the Galápagos makes understanding the mechanisms and factors of speciation, the engine of biodiversity, important, and timely. While speciation in marine archipelagos has been described in the past, such as for cone snails in Cabo Verde Archipelago and limpets in Hawaii, adaptive radiations in the marine environment are still rare and poorly understood. In this study, we focused on the Galápagos blue-banded goby, Lythrypnus gilberti, a small endemic fish that is found in shallow subtidal rocky habitats. Using RAD sequencing, we analyzed 19,504 loci that were either neutral, or potentially under directional selection. As expected, considering the small geographic range, population structure based on neutral markers was weak. For loci under directional selection, however, marked differences between islands suggested potential for local adaptation. Our data suggest that for marine species, where dispersal barriers are less apparent, mechanisms of local adaptation may also be at play in the Galápagos Archipelago.