Population dynamics and genetic differentiation in the bivalve mollusc Abra tenuis: aplanic dispersal

Abstract

The bivalve mollusc Abra tenuis is an aplanic (directly developing) species occupying a discontinuous (fragmented) habitat in the high intertidal area of mudflats. In view of its mode of reproduction and habitat, populations of A. tenuis should exhibit temporal stability and be geneti- cally dissimilar. Examination of the population dynamics of A. tenuis, at 2 sites in the Dutch Western Wadden Sea over the last 29 yr, has revealed that population densities fluctuate wildly from year to year, and that there have been 2 'apparent' local extinction events, one of which lasted for 3 yr. Inves- tigation into the population genetics of Abra tenuis in the Dutch Western Wadden Sea, using random amplified polymorphic DNA (RAPD) analysis, both at the macro (≥2 km) and microscale (≥30 m), determined that 6 of the 7 studied populations formed 3 groups that were genetically homogenous within a group, but genetically distinct from each other. This included a group pair where the dis- tance of geographical separation was ~3 km. The 7th population was genetically distinct from all other population groups. While there is some degree of genetic differentiation among populations, given both the population genetics and dynamics results, it is evident that dispersal has occurred among some populations.