A Tale of Two Skates: Comparative Phylogeography of North American Skate Species with Implications for Conservation

Genomic data can provide novel insights into the natural history of oceanic species. These data can inform the management of vulnerable and slow-maturing species by estimating population structure, rates of migration, and the distribution of genetic diversity. In this study we focus on two protected elasmobranch species, the Winter Skate, Leucoraja ocellata, and the Little Skate, L. erinacea. We use genome-wide SNPs to estimate population structure, and quantify migration and genetic diversity among both species from four sampling localities across the Atlantic coast of North America. We find that species of Leucoraja are generally isolated by distance, although we infer some fine-scale population structure. Specifically, estimates of effective migration infer fine-scale population structure in L. ocellata between the northern sites of Georges Bank and the Mid-Atlantic sampling sites, whereas L. erinacea shows no evidence of population genetic structure in any analyses. We also found that genetic diversity is concentrated in the central sites of Georges Bank and the Mid-Atlantic Bight for L. ocellata, but is reduced at these two sites in L. erinacea, suggesting opposite distributions of genetic diversity between species. Thus, genomic data suggest that while species of Leucoraja lack discrete population structure, they likely employ only mid-range dispersal. These findings correspond to ecological studies that have found eco-physiological differences between embryonic and juvenile Leucoraja from different localities. Taken together, small-bodied skate research emphasizes the importance of local adaptive plasticity for marine species, even without population genetic structure. Conservation strategies should focus on managing the portions of the Atlantic coast considered most vital to reproduction of Leucoraja, but should not recognize multiple populations across their range.