Pattern of genetic isolation in the crab pachygrapsus marmoratus within the tuscan archipelago (Mediterranean Sea)

Abstract

The genetic connectivity level of the benthic crab Pachygrapsus marmoratus was assessed within the Tuscan Archipelago, an area between the Ligurian and Tyrrhenian Seas, Italy. The archipelago comprises 7 islands lying inside the largest marine protected area of the Mediterranean Sea. We genotyped a total of approximately 230 individuals from 8 populations (4 protected and 4 unprotected) at 8 microsatellites. Overall, our results showed a clear partitioning of genetic variation within this area; all populations were separated from one another, except the 2 southernmost islands. This genetic subdivision could be due to a 'sweepstakes reproductive effect' (i.e. only a small proportion of the available gene pool successfully contributes to the replenishment of each population). Furthermore, the lack of a pattern of isolation by distance, coupled with a low percentage of individuals assigned to their own populations, indicates that retention of larvae near the parent population is unlikely to be the main cause of the recorded genetic structure. However, we also found evidence of past demographic events in all populations, which may have played a pivotal role in shaping the recorded pattern of intraspecific differentiation. Finally, we did not detect any difference in the level of genetic variation between populations that were protected (i.e. experiencing less human pressure) and those that were unprotected. This suggests that, from a genetic point of view, the effects of protection have not yet been demonstrated. © Inter-Research 2013.