Overdominance of a Muscle Protein ( Mp -1) Locus in the Japanese Oyster, Crassostrea gigas (Ostreidae)

• Published in: Journal of the Fisheries Research Board of Canada
• Main Author: Buroker, N. E.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1979
• Subjects: General Medicine; Crassostrea gigas
• Online Access: http://dx.doi.org/10.1139/f79-189; http://www.nrcresearchpress.com/doi/pdf/10.1139/f79-189

A microgeographical population genetic study of the Japanese oyster, Crassostrea gigas, revealed a case of overdominance for a muscle protein (Mp-1) locus. This locus consists of a two allele polymorphism. A study of the relative "fitness" of the three genotypes (Mp-1 105/105 , Mp-1 105/100 , and Mp-1 100/100 ) revealed a heterozygote superiority in the segment of the oyster population at the lowest tidal level (+ 1.2 m). In segments of the population at higher tidal heights (i.e. + 1.8 and + 2.4 m), there appears to be a selective advantage for Mp-1 105 allele since the highest "fitness" values belong to the Mp-1 105/105 genotype. Since oysters do not appear at the field station lower than 1.2 tidal m, it could not be determined if the Mp-1 100 allele had a selective advantage at tidal levels lower than 1.2 m. However, the Mp-1 105 allele possibly exhibits a selective advantage in the subtropical marine environment of southern Japan, while the Mp-1 100 allele is favored in the temperate marine environment of northern Japan. This suggests perhaps that a micro- and macrogeographical cline in gene frequency exists for the Mp-1 locus due to a thermal gradient. Key words: Japanese oyster, Crassostrea gigas, population genetic study, overdominance, heterozygote superiority, Mp-1 locus, micro- and macrogeographical cline, thermal gradient, tidal height, latitude