Abstract
AIM: Evolutionary history of natural populations can be confounded by human intervention such as the case of decorator worm species Diopatra (Onuphidae), which have a history of being transported through anthropogenic activities. Because they build tubes and act as ecosystem engineers, they can have a large impact on the overall ecosystem in which they occur. One conspicuous member, Diopatra biscayensis, which was only described in 2012, has a fragmented distribution that includes the Bay of Biscay and the Normanno-Breton Gulf in the English Channel. This study explores the origin of these worms in the Normanno-Breton region, which has been debated to either be the result of a historic range contraction from a relic continuous population or a more recent introduction. LOCATION: Northeastern Atlantic, the Bay of Biscay, and the Normanno-Breton Gulf. METHODS: We utilized a RAD-tag-based SNP approach to create a reduced genomic data set to recover fine-scale population structure and infer which hypothesis best describes the D. biscayensis biogeographic distribution. The reduced genomic data set was used to calculate standard genetic diversities and genetic differentiation statistics, and utilized various clustering analyses, including PCAs, DAPC, and admixture. RESULTS: Clustering analyses were consistent with D. biscayensis as a single population spanning the Bay of Biscay to the Normanno-Breton Gulf in the English Channel, although unexpected genetic substructure was recovered from Arcachon Bay, in the middle of its geographic range. Consistent with a hypothesized introduction, the isolated Sainte-Anne locality in the Normanno-Breton Gulf was recovered to be a subset of the diversity found in the rest of the Bay of Biscay. MAIN CONCLUSIONS: These results are congruent with previous simulations that did not support connectivity from the Bay of Biscay to the Normanno-Breton Gulf by natural dispersal. These genomic findings, with support from previous climatic studies, further support the hypothesis that D. biscayensis phylogeographic connectivity is the result of introductions, likely through the regions' rich shellfish aquaculture, and not of a historically held range contraction.