Abstracts (first author)
High relatedness and chaotic genetic patchiness of a polychaete in a heterogeneous estuarine landscape
Population genetic structure in marine organisms frequently defies clear explanation and is described as chaotic genetic patchiness. In these cases, patterns of genetic structure may be determined by barriers to dispersal that are difficult to observe, e.g., those created by variable oceanic currents or by the behavior of dispersive larvae and adults. We examined population genetic structure using seven microsatellite loci in the polychaete worm, Pygospio elegans, sampled from 16 sites in a heterogeneous estuarine landscape in Denmark. Most samples showed significant pairwise Fst and Jost’s D, and there was no indication of isolation by distance. Using GESTE, we calculated sample-specific Fst values, which characterize how the samples differ from the metapopulation as a whole. Variation in these estimates was not explained by environmental variables, including salinity, substrate, and distance from the mouth of the estuary. The samples most dissimilar in terms of observed allele frequencies, and those with high estimated numbers of siblings, had larger sample-specific Fst. We hypothesize that polymorphism in the developmental mode of P. elegans, which produces both dispersive planktonic larvae and non-dispersive larvae brooded by the mother, contributes to chaotic genetic patchiness in this estuarine landscape. The large numbers of siblings estimated within samples could reflect high local recruitment of brooded larvae, despite effective dispersal and high gene flow via planktonic larvae.