Multilocus heterozygosity and size: A test of hypotheses using triploid mytilus edulis

Abstract

Cohorts of meiosis I and meiosis II induced triploid Mytilus edulis were produced from mass matings in the laboratory and reared alongside normal diploid cohorts during 1990 and 1991. Diploid cohorts generally exhibited a significant positive correlation between multilocus heterozygosity and size. This correlation was absent or much more weakly expressed in cohorts of triploid mussels and this supports the ‘associative overdominance’ hypothesis rather than the ‘direct involvement’ hypothesis as the major explanation for the correlation. For both diploids and triploids, no correlation between heterozygosity and the coefficient of variation of size was evident and heterozygotes at single loci were not larger than homozygotes. Triallelic triploid heterozygotes were no larger than diallelic triploids. The diploid cohorts were generally in agreement with the Hardy-Weinberg model and there was no trend towards heterozygote deficiency. © 1995 The Genetical Society of Great Britain.