HETEROZYGOTE DEFICIENCIES IN A COHORT OF NEWLY SETTLED MYTILUS-EDULISSPAT

A cohort of newly settled Mytilus edulis (L.) (Mollusca: Bivalvia) spa t (mean shell length 530 mum) was collected from red filamentous algae at a site on the North Wales coast. After a period of growth in the l aboratory, cellulose acetate and starch gel electrophoresis were used to investigate genotype frequencies at the Gpi, Odh, Lap, Pgm, Idh and Mpi loci. Individual testing of each locus, using the chi2 test, reve aled significant deficiencies of heterozygotes at the Pgm, Mpi and Idh loci. However, further testing using a sequential Bonferroni test, de signed to assess the probability of observing at least one significant result from a number of tests by chance alone, revealed that only the deficiency of heterozygotes at Pgm and Mpi loci was significant at th e table-wide 95% level. Since post-collection mortality was <3%, these heterozygote deficits must have existed at the time of collection. Th e conclusion drawn is that heterozygote deficiencies in mussels are ge nerated during the larval stage or at early settlement.