Dispersal vs. retention: correspondence of species-specific reproductive cycles and settlement periods in a blue mussel hybrid zone

Abstract

While long distance dispersal of planktotrophic larvae in marine organisms has tradi- tionally been considered the norm, several recent studies have shown that local retention of larvae and hydrodynamic barriers to dispersal often exist. This study focuses on the question of whether genetically distinct populations within a blue mussel hybrid zone typically exchange larvae or if larvae are often retained within the population of origin. Larvae were tracked to their point of settle- ment using a genetic marker and analyzed for correlations with differential timing of reproduction and settlement among 3 genetically distinct populations (Mytilus edulis, M. galloprovincialis and hybrid). Correspondence of allele frequencies to local reproduction and settlement suggest that larvae settling within the M. edulis and the hybrid zone populations originated from those locations. On the other hand, larvae settling within the M. galloprovincialis populations often contain signifi- cant proportions of immigrants from the hybrid zone. The observed patterns are consistent with pre- vious studies of the local hydrodynamics, suggesting that physical barriers to dispersal often exist and result in retention of larvae.