Does enzyme heterozygosity influence developmental rate in rainbow trout?

The association between genetic variation at 14 enzyme loci and developmental rate was examined in six strains of rainbow trout (Salmo gairdneri). The purpose of this study was to test the prediction that heterozygotes develop faster than homozygotes. We also tested whether the enzyme loci could be responsible for such an association or are marking chromosomal segments that influence developmental rate. There is a significant negative association (P less than 0.05) between hatching time and the number of heterozygous loci per fish in one of six strains. Heterozygotes developed faster than homozygotes at 26 out of 43 possible comparisons made at individual loci within strains. Heterozygotes developed significantly faster than homozygotes in eight comparisons, and significantly slower in six comparisons. These results suggest a weak positive association between developmental rate and heterozygosity. Nine loci were polymorphic in more than one strain. At five of these loci the hatching distributions of heterozygotes and homozygotes are significantly different among strains. The direction of the relationship between heterozygosity and developmental rate at individual loci is not consistent among strains. Therefore, our results suggest that the loci surveyed are marking chromosomal segments that influence developmental rate. Linkage disequilibrium between alleles at the isozyme loci and dominant-acting genes that accelerate or retard developmental rate is hypothesised to account for the observed relationship between heterozygosity and developmental rate.