MULTILOCUS HETEROZYGOSITY AND SIZE - A TEST OF HYPOTHESES USING TRIPLOID MYTILUS-EDULIS

Cohorts of meiosis I and meiosis II induced triploid Mytilus edulis we re produced from mass matings in the laboratory and reared alongside n ormal diploid cohorts during 1990 and 1991. Diploid cohorts generally exhibited a significant positive correlation between multilocus hetero zygosity and size. This correlation was absent or much more weakly exp ressed in cohorts of triploid mussels and this supports the 'associati ve overdominance' hypothesis rather than the 'direct involvement' hypo thesis as the major explanation for the correlation. For both diploids and triploids, no correlation between heterozygosity and the coeffici ent of variation of size was evident and heterozygotes at single loci were not larger than homozygotes. Triallelic triploid heterozygotes we re no larger than diallelic triploids. The diploid cohorts were genera lly in agreement with the Hardy-Weinberg model and there was no trend towards heterozygote deficiency.