Genetic Divergence And Loss Of Diversity In Two Cultured Populations Of The Bay Scallop, Argopecten Irradians (Lamarck, 1819)

Researchers at the Virginia Institute of Marine Science (VIMS) have been maintaining a small-scale bay scallop (Argopecten irradians) culturing operation since the late 1960s. The cultured Line was originally established with broodstock collected from the coasts of Virginia and North Carolina, but it has since been augmented with a \u27\u27grab bag\u27\u27 of introductions from other source populations. A large bay scallop-culturing operation was reportedly founded in China in the early 1980s, with 26 individuals provided by the VIMS researchers. The degree of genetic divergence between these two populations since the founding of the Chinese operation is unknown, as are the relative amounts of genetic diversity that may have been maintained under the selective pressures of the hatchery. Samples of cultured bay scallops were obtained from culturing operations in Wachapreague, VA, in 1993 and 1995, and from the Shandong Province of China in 1993. Mitochondrial DNA (mtDNA) was isolated from individual scallops, digested with a battery of eight restriction enzymes, and analyzed by restriction fragment length polymorphism analysis. Measures of haplotype diversity and divergence were calculated for the samples to reveal genetic differences between the cultured populations and to allow comparison of the levels of genetic variation maintained in the cultured populations relative to those observed in several natural populations of bay scallops. A sample of 55 Virginia cultured bay scallops was found to be monotypic, represented by a single haplotype, and three haplotypes were observed in 36 individuals sampled from China. No haplotypes were shared between the samples, indicating that significant divergence has occurred between the populations. The single haplotype from Virginia was observed in a sample of bay scallops from New England, and the least common haplotype from the Chinese sample was also found in samples from New England, North Caroling and Crystal River, FL. Haplotype diversity and genotypic divergence values for the cultured samples indicate that mtDNA variation may be lost in the culturing process and that a bottleneck effect and/or genetic drift has affected the levels of variation in these populations differently. Assuming that the Chinese culturing operation was founded exclusively with individuals from the Virginia population, it can be concluded that the latter has lost a greater proportion of the original variation in the intervening generations of hatchery breeding