Genetic population structure of the swimming crab Callinectes danae (Crustacea: Decapoda) in southern Brazil

The population genetic structure of the swimming crab Callinectes danae (Crustacea, Portunidae) was studied by allozyme electrophoresis along the southern coast of Brazil (Santa Catarina and Rio Grande do Sul States). The biology of C. danae is poorly known, but some studies suggest that this species depends on estuaries for reproduction and for completing its life cycle, using them as recruitment sites and nursery grounds. If estuarine retention is an important process acting in favour of the recruitment of local populations, we should expect restriction of gene flow among populations inhabiting different estuaries. Therefore, our aim was to establish whether gene flow between populations of C. danae from different estuaries was restricted. Samples were collected in four estuaries: Sao Francisco do Sul, Laguna (Santa Catarina), Patos Lagoon and Chui Stream (Rio Grande do Sul). Eleven loci were resolved. Contingency table tests (chi(2) and G) showed significant differences (P less than or equal to 0.05) between pair-wise subpopulation comparisons. The estimated F-ST was theta=0.065 +/- 0.019, suggesting a moderate structuring of C. danae populations. No relationship was found for the number of migrants between pairs of subpopulations and the geographic distance separating them (P=0.292; r(2)=0.269). Nevertheless, UPGMA analysis clustered together those estuaries separated by less than 250 km. Low adult migration, the requirement of estuaries as reproductive areas, recruitment sites and nursery grounds for juveniles, together with larval and post-larval retention processes, are discussed in the context of their importance in preventing panmixia among subpopulations inhabiting different estuaries.