MITOCHONDRIAL-DNA VARIATION IN INTRODUCED POPULATIONS OF PACIFIC OYSTER, CRASSOSTREA-GIGAS, IN BRITISH-COLUMBIA

Crassostrea gigas, a species native to Japan, was transplanted in very large numbers from the Miyagi Prefecture from 1927 to 1977 to British Columbia coastal waters. We examined the genetic structure and diversity of wild British Columbian populations of C. gigas using restriction enzyme analysis of mitochondrial DNA. Forty-four mtDNA haplotypes were identified in 141 animals from the populations sampled, implying the existence of considerable genetic diversity. The frequency distribution of these haplotypes is unusual in that only two haplotypes predominate whereas 34 are represented by a single individual and five by two individuals. The four British Columbia populations sampled all shared the two common haplotypes in roughly the same frequencies and a third haplotype at low frequencies. Between 9 and 11 haplotypes were found uniquely in each of the four British Columbia populations sampled, but 34 of those 40 private haplotypes were observed only once. Much larger sample sizes would be required to conclude that those haplotypes are indeed ''private'' and not present in low frequencies in all populations. We conclude that there is substantial genetic variation in these introduced populations, but there is little evidence of genetic divergence between them.