DOI: 10.5061/dryad.cjsxksn6r
title: Genetic structure and dispersal in peripheral populations of a marine fish (Pacific cod, Gadus macrocephalus) and their importance for adaptation to climate change

description: Small and isolated peripheral populations, which are often remnants of
 glacial refugia, offer an opportunity to determine the magnitude and
 direction of fine-scale connectivity in high gene flow marine species.
 When located at the equatorial edge of a species’ range, these populations
 may also harbor genetic diversity related to survival and reproduction at
 higher temperatures, a critical resource for marine species facing warming
 ocean temperatures. Pacific cod (Gadus macrocephalus), a marine fish in
 the North Pacific, has already experienced major shifts in biomass and
 distribution linked to climate change. We estimated the magnitude and
 direction of connectivity between peripheral populations of Pacific cod at
 the southern edge of the species’ range, by conducting restriction
 site-associated DNA (RAD) sequencing and individual assignment on fish
 collected around the Korean Peninsula during the spawning season. Three
 populations on the western, eastern, and southern Korean coasts were
 highly differentiated (FST =0.025 – 0.042) and relatively small (Ne =
 433-1777). Ten putative dispersers and estimates of contemporary migration
 rates revealed asymmetrical, west-to-east movement around the Korean
 Peninsula, at a higher rate than predicted by indirect estimates of
 connectivity (FST). Allele frequencies at 87 RAD loci were decisively
 correlated with strong marine temperature gradients between the warmer
 southern coast and the cooler waters of the eastern and western coasts.
 Despite relatively small sample sizes, our data suggest asymmetrical
 dispersal and gene flow, potentially involving adaptive alleles, between
 peripheral populations inhabiting markedly different thermal regimes. Our
 study emphasizes the conservation value of peripheral populations in high
 gene flow marine fish species.
description: Fin clips and tissue samples were collected from aggregations of
 Pacific cod at known spawning sites around the Korean Peninsula, during
 the spawning season. Restriction site-associated DNA (RAD) libraries were
 prepared according to Baird et al. (2008) and Etter et al. (2011), with
 modifications developed for North American Pacific cod samples by Drinan
 et al. (2018). RAD-sequencing data was processed using the Stacks v1.44
 pipeline (Catchen et al., 2011; Catchen et al., 2013), Bowtie (Langmead et
 al., 2009), and NCBI’s Basic Local Alignment Search Tool, BLAST (Altschul
 et al., 1990), per Drinan et al. (2018) and Brieuc et al.
 (2014). Please see the associated publication for
 methodology details.  
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