Superior Developmental Stability of Heterozygotes at Enzyme Loci in Salmonid Fishes

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Abstract
The association between heterozygosity at 42 enzyme loci and fluctuating asymmetry at 5 bilateral meristic characters was examined 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 2 populations of rainbow trout and 2 populations of cutthroat trout. This correlation is negative in 13 of the 14 population samples (sign test, P < 0.001). Individuals that are more heterozygous at isozyme loci have reduced fluctuating asymmetry; this appears to be general among salmonid fish. Individuals with obvious morphologic deformities in 3 populations have increased fluctuating asymmetry. 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 morphologic deformities suggest that heterozygosity is positively correlated with fitness in these fish.