Spatial genetic structure in Themisto libellula (Amphipoda: Hyperiidae) from the coastal Gulf of Alaska, Bering and Chukchi seas

Abstract

Arctic marine ecosystems are undergoing rapid biogeographic responses to climate changes following the highest warming rates observed around the globe in recent decades. These drastic changes undoubtfully affect gene flow and genetic structure in the polar and subpolar regions. Here, we examine the genetic structure of the cold-water holozooplankton hyperiid Themisto libellula (Amphipoda: Hyperiidae), a key species in the Arctic ecosystem, using molecular population genetic approach. For the first time, we examine and compare populations across the Arcto-Pacific sector of the species biographical range from the northern Gulf of Alaska through the northern Chukchi Sea. We hypothesized that the complex history of the North Pacific and Amerasian Arctic marked by periodic intermissions and restrictions of the dominant northward flow resulted in vicariant differentiation of T. libellula along the latitudinal gradient. Mitochondrial and Rad-sequencing analyses revealed little genetic differentiation between closely connected Arctic populations in the Arctic Chukchi and Bering seas. In contrast, population from sub-Arctic glacial fjords in the Gulf of Alaska were distinct with few shared COI haplotypes. Strong FST estimates (FST = 0.16) based on 5197 neutral SNPs between the Gulf of Alaska and Bering Sea populations indicated very limited exchanges despite an existing connection between the areas via the Alaska Coastal Current. Our results suggest strong opportunities for genetic differentiation among marine zooplankton populations along the Pacific Alaskan coast and from the Arctic marginal seas.