Meeting Abstract

S3.6  Tuesday, Jan. 4  Assortative fertilization across hybrid genotypes promotes reproductive isolation in a bimodal hybrid zone between Mytilus blue mussels MCCARTNEY, MA*; SCHMIDT, VS; Univ. of North Carolina, Wilmington; MBL, Woods Hole mccartneym@uncw.edu

Support for the view that hybrid zones demonstrate speciation in progress (rather than its failure to complete) comes from comparative studies of genotype distributions. Flat or unimodal zones (intermediate genotypes dominate) may represent earlier stages, and bimodal zones (intermediate genotypes uncommon) later stages in a succession towards full speciation. That assortative mating and fertilization are associated with bimodality suggests an involvement in driving speciation, but the strength and causes of assortative mating are more poorly understood in hybrid zones. This is in part because compatibility between the range of combinations between hybrid and non-hybrid mates is rarely evaluated. We studied assortative fertilization in vitro across the full spectrum of combinations between pure and hybrid genotypes in the western Altantic bimodal hybrid zone between blue mussels Mytilus edulis and M. trossulus. We find assortative fertilization not only between pure parentals, but also between hybrids, with its strength increasing with the number of species-diagnostic marker alleles shared between mates. In contrast, sharing of species-specific alleles at the putative gamete recognition locus M7 lysin did not contribute to compatibility. The results underscore the potential for assortative mating to promote progress towards speciation in hybrid zones of free spawning animals.