Analysis of population genetic structure of the green sea urchin (Strongylocentrotus droebachiensis) using microsatellites

We measured within- and among-population genetic variation in the green sea urchin (Strongylocentrotus droebachiensis) at 11 sites in the north Atlantic and northeast Pacific by using four-locus microsatellite genotypes. We found no differentiation among populations from Atlantic Canada, but strong differentiation across the north Atlantic and between the Atlantic and Pacific samples. High inbreeding coefficients at three loci are consistent with high variance in reproductive success. One population that was recently decimated by disease was strongly differentiated from some others, but there was little differentiation otherwise among populations in Atlantic Canada. On a larger scale, populations in Atlantic Canada were more similar to a population from the north Pacific than to populations in the northwest Atlantic. Differentiation among populations at this large spatial scale is consistent with biogeographical hypotheses of: (1) Pleistocene population reduction and isolation in the northeast Atlantic, but (2) extinction in the northwest Atlantic followed by extensive recolonization from the Pacific. In contrast to other recent studies of trans-Atlantic organisms, we found no evidence of extensive gene flow across the north Atlantic.