New genetic markers reveal population genetic structure at different spatial scales in the opportunistic polychaete Pygospio elegans

Identifying population genetic structure can shed light on how life history characteristics of opportunistic species affect population turnover and (re)colonization of disturbed habitats. Plasticity in life history traits can be particularly important for opportunistic species. In this study, we investigated population genetic structure of two populations of Pygospio elegans, an opportunistic polychaete worm. The populations represented extremes of the range of habitats P. elegans exploits: a subtidal brackish site where P. elegans is found at lower densities associated with seagrass patches; and a disturbed mudflat in a marine tidal environment where P. elegans can reach very high densities with patchy distribution. Eight novel microsatellite loci were isolated from P. elegans for the genetic studies. We found higher genetic diversity in the mudflat, which could be due to larger population size, opportunistic behaviour, or the predominantly planktonic larval production of P. elegans in this population. No genetic structure was found within the seagrass patch in the Archipelago Sea (SW Finland) where samples were separated by 5–15 m. However, low structure was observed in the Bay of Somme, mudflat (France) where samples were separated by approx. 100 m. When the two locations were compared, high genetic differentiation was observed, indicating restrictions on gene flow between the sea areas. The microsatellite loci were highly polymorphic and proved to be useful tools for investigating the genetic diversity and genetic structure in P. elegans at different spatial scales, despite deviations from Hardy–Weinberg expectations at some loci.