Superior developmental stability of heterozygotes at enzyme loci in salmonid fishes

We examined the association between heterozygosity at 42 enzyme loci and fluctuating asymmetry at five bilateral meristic characters in 14 population samples of rainbow trout, cutthroat trout, and brook trout. There is a significant negative correlation between heterozygosity and the proportion of asymmetric characters per individual in two populations of rainbow trout and two populations of cutthroat trout. This correlation is negative in 13 of the 14 population samples (sign test, P < .001). Thus, individuals that are more heterozygous at isozyme loci have reduced fluctuating asymmetry; this appears to be general among salmonid fishes. We also found that individuals with obvious morphological deformities in three populations have increased fluctuating asymmetry. Thus, fluctuating asymmetry appears to be a reliable indicator of overall developmental stability and is therefore negatively correlated with fitness. The association between heterozygosity and asymmetry and between asymmetry and morphological deformities suggest that heterozygosity is positively correlated with fitness in these fishes.