INHERITANCE OF MERISTIC VARIATION AND THE EVOLUTION OF DEVELOPMENTAL STABILITY IN RAINBOW TROUT.

We found relatively high heritabilities in the narrow sense for seven of eight meristic characters in a population of rainbow trout using regression of mean progeny values on mid-parent values. In sharp contrast, there is no statistically significant additive genetic variance controlling developmental stability, as measured by fluctuating asymmetry (h = 0.02). However, there is a significant correlation between the average heterozygosity of each family at isozyme loci and the average number of asymmetric traits per individual. We have previously reported a strong correlation between heterozygosity at protein loci and decreased fluctuating asymmetry in this and other salmonid populations. Thus, there is little or no additive, but substantial dominance, genetic variation affecting fluctuating asymmetry. This suggests that there has been directional selection for increased developmental stability.