GENETIC-VARIATION AMONG POPULATIONS OF MYTILUS SPP IN EASTERN NEWFOUNDLAND

Limited sampling of Mytilus spp. in eastern Newfoundland has suggested that M. trossulus Gould and M. edulis L. are distributed as pure popu lations or mixtures of both species. In 1989 and 1990 we collected a w ider series of samples of Mytilus spp. from 16 sites in eastern Newfou ndland in order to determine the genetic structure based on four polym orphic enzyme loci (Est, Pgm, Lap, Ap). Associations among loci (parti cularly Pgm and Est), and a bimodal distribution of individual princip al-component scores (based on four-locus genotypes) provided evidence for the presence of both M. trossulus and M. edulis. Most of the sites consisted of a mixture of the two species. The relative frequency of each species in the samples varied on both a macro- and microgeographi c scale. Two wave-exposed sites had the highest frequency (>90%) of M. trossulus. The distribution of hybrid index scores, based on three pa rtially diagnostic loci (Est, Pgm, Lap), provided no evidence for hybr idization.