Genetic and morphological variation in the mussel Mytilus in Newfoundland

The genus Mytilus in Newfoundland is thought to be differentiated into two taxa, presently called M. trossulus and M. edulis. In the present study a survey of the distribution of these two taxa was undertaken. Ten sites along the east coast of Newfoundland were sampled; two of these sites were sampled on a finer scale. Four partially diagnostic enzyme loci, Pgm, Est, Lap, and Ap differentiated two groups. Both groups were found at most sites. Heterozygote deficiencies (relative to Hardy Weinberg Equilibrium) were found in one or more loci at all but one site. However the presence of some heterozygotes suggests that the two taxa interbreed. Pgm, Est, and Lap genotypes were significantly associated and together were useful in separating the two taxa. -- Inner shell colour was correlated with enzyme genotype, M. trossulus being relatively darker than M. edulis, but this failed to be a robust taxonomic character across all sites. In a fine scale analysis at Traytown, genotype frequency was found to be correlated with increasing shell length. This suggests variation in recruitment, growth and/or mortality between the two taxa