RAWSON, P*; SLAUGHTER, C; YUND, P: Asymmetric Gametic Incompatibility Among Two Species of Marine Mussel

Two species of blue mussel, Mytilus edulis and M. trossulus, are sympatric on the east coast of North America. Although mussels with hybrid genotypes are commonly observed in this region, the frequency of hybrids is low relative to other mussel hybrid zones. We have initiated several studies investigating the ecological and genetic factors that may restrict hybridization between M. edulis and M. trossulus. In the summer of 2001, we conducted a series of intra- and inter-specific matings with these two species to test the hypothesis that limited inter-specific fertilization success contributes to a reduced frequency of hybrids. Our results indicate that gametes from these two species are generally incompatible; when interspecific crosses are successful, gametic compatibility is highly asymmetric. While M. edulis sperm can only fertilize M. trossulus eggs when present at extremely high concentrations, occasionally M. trossulus sperm are as successful at fertilizing M. edulis eggs as they are at fertilizing M. trossulus eggs. In addition, our results suggest that successful cross-fertilization between these species is dependent upon the source of the eggs (ie. particular M. edulis females) but not necessarily on the source of sperm.