MEPS 253:183-195 (2003)  -  doi:10.3354/meps253183

ABSTRACT: Human-mediated biological invasions are known to threaten biodiversity and are often the cause of economic problems, mainly via interspecific interactions with commercially valuable indigenous species. The hermaphroditic gastropod Crepidula fornicata (L.) is a successful marine invader of European coasts. In France, it was first recorded in the 1940s and now proliferates, competing with cultured and fished bivalves. To analyze the patterns of spread and the genetic architecture of the populations of this invader, 13 populations, 12 French and 1 native (American) (N = 660) were sexed and analyzed using 8 polymorphic enzyme loci. The majority of the populations showed balanced sex ratios. A high level of genetic diversity was detected in the French populations, contrary to the usual pattern of founder effect frequently reported for invaders. Moreover, most of the introduced populations were shown to be in migration-drift equilibrium. Thus, our results suggest that, in its introduced range, C. fornicata has stable populations and behaves genetically and demographically in the same way that it does over its native range. The pattern among French populations suggests that the introduction process was complex, and that C. fornicata from France derives from several genetically diverse, but poorly differentiated, source populations. Finally, this dataset also showed that the effects of shell-farmer-mediated transport between bays are only detectable at some specific localities. On the other hand, there was a good fit between patterns of genetic differentiation and the major hydrodynamic features along the French coasts, strongly suggesting that larval dispersal plays an important role in the spread of C. fornicata in Europe.

KEY WORDS: Biological invasion · Slipper-limpet · Founder effect · Dispersal · Genetic diversity · Protandry