Biogeography of Beringian fishes after the molecular revolution and into the post-genomics era

Significant progress in our knowledge of Beringian biodiversity and in the technologies available for biodiversity research has been made in the several decades since a comprehensive biogeographic synthesis of Beringian freshwater fishes was compiled and published in 1986. Further, the fish fauna of Beringia and, more broadly, of high latitude freshwater systems of the northern hemisphere face some of the most intense well documented effects of global climate change. Here we synthesize current understanding of how the dynamic spatial and ecological landscapes of Pleistocene glaciations have shaped the distribution of taxonomic and genetic diversity in fish faunas of Beringia. Through a more complete integration of knowledge obtained in studies of fishes in Russian drainages, we aimed to identify promising strategies to test alternative biogeographic hypotheses on the roles played by the Bering land bridge, paleorivers and glacial history in intercontinental faunal movement. We focus on freshwater fishes of the Bering Strait region, which live in an environment that is premised on extreme instability and profound changes in long-term connectivity for fishes and offers opportunities to assess long-term evolutionary trends in both speciation and life history variation. Such information is critical for both our scientific understanding of evolutionary processes in fishes and valuable for those tasked with the challenges of management and conservation of natural resources in this expansive, dynamic and remote region. We provide an overview of Beringian freshwater ichthyofauna and examine genetic differentiation among population units within these lineages. We also examine evidence for how long population units have been separated based on historic glacially-related separations and the more recent marine barrier of the Bering Strait that constrains freshwater or diadromous species based on their ability to disperse in salt water. Our review concludes on how Arctic and sub-Arctic fishes may adapt and persist in their dynamic environment considering low genetic diversity, the role of adaptive introgression, and epigenetic variation. We find that Beringian fishes may poorly fit traditional taxonomic categories and the designation of conservation units below the species level may be of great practical application. Furthermore, as hybridization is documented to increase in the Arctic, the use of this process for ecological monitoring may also be of high utility with Beringian fishes.