Changes in molecular genetic variation at AFLP loci associated with naturalization and domestication of the Pacific oyster (
The Pacific oyster (Crassostrea gigas) is an important commercial species in the US Pacific Northwest with a history of production initially based on wild-caught seed imported directly from the Miyagi region of northern Japan (1920s–1970s) followed by an extended period of seed collection from a small number of naturalized, self-recruiting populations in US estuaries (early 1970s-present) and more recently through large-scale hatchery production of seed oysters (mid 1970s-present). I studied the genetic level consequences of each of these major transformations of the oyster industry by examining the patterns of private alleles (bands unique to one sample), the number of polymorphic loci, expected heterozygosity, genetic distance between populations and genetic divergence between individuals within and among three native Pacific oyster populations in Japan (Hiroshima, Miyagi, Midori River), five naturalized populations in North America (Pipestem Inlet BC, Nootka Inlet BC, Dabob Bay WA, Willapa Bay, WA, and Tillamook Bay, OR), two in New Zealand (Chance Bay and Kaipara Harbor), and seven domesticated and selectively bred cohorts from an ongoing genetic improvement program on the West Coast of the United States using amplified fragment length polymorphism (AFLP) markers. All but one of the naturalized populations in both the USA and New Zealand are genetically more similar to native populations from the Ariake Sea (Midori River) than to the Miyagi region of their origin, but all domesticated stocks more closely resemble the wild Miyagi population. According to local oyster producers, the one exceptional naturalized population (Tillamook) is a very recent colonization derived from farmed oysters. Such consistency is unexpected under random genetic drift, and I speculate that both natural and artificial selection may have altered AFLP allele frequencies in this species in the course of naturalization and domestication.