Genetic studies of laboratory reared Mytilus edulis.: II. Selection at the leucine amino peptidase (Lap) locus

Abstract

Offspring from several families and a mass mating of Mytilus edulis were cultured in the laboratory up to the juvenile stage under different temperature regimes. Mussels were genotyped at the leucine aminopeptidase (Lap) locus at the spat stage (post-metamorphosis) using cellulose acetate electrophoresis and at the juvenile stage using starch gel electrophoresis. Significant deviations from expected genotype frequencies were found in many cultures at both stages and certain genotypes were generally found to be favoured irrespective of temperature regime during culture. Estimates of relative fitnesses of the six common Lap genotypes suggest overdominance for the alleles Lap94 and Lap96 and semi-dominance for Lap98, but calculations based on this array of estimated fitnesses indicate that Lap98 would eventually become fixed in a panmictic population. Since a balanced Lap polymorphism exists in the wild we conclude that selection differentials at the Lap locus in laboratory cultures may be very different from those in nature, and suggest that nutritional constraints may account for some of these differences in selection. Also, in contrast to wild populations, the laboratory cultures showed a significant excess of Lap heterozygotes. © 1989, The Genetical Society of Great Britain.