Heterozygosity and developmental stability in gynogenetic diploid and triploid rainbow trout.

We have previously reported that rainbow trout (Salmo gairdneri) more heterozygous at enzyme loci generally show increased developmental stability, as measured by reduced fluctuating asymmetry. We experimentally produced gynogenetic diploid and triploid individuals to test the effect of extreme heterozygosities on developmental stability. Gynogenetic diploids are identical by descent at an estimated 34 per cent of all loci and show a 50 per cent increase in the mean proportion of traits asymmetric per individual compared to normal rainbow trout. Triploids from two different strains have an estimated 30 per cent increase in genomic heterozygosity and a 14 per cent decrease in the mean proportion of traits asymmetric per individual compared to normal diploids. These changes in asymmetry induced by gynogenesis and triploidy are not as great as we expected based on the association between heterozygosity and fluctuating asymmetry in random mating populations. The narrow range of mean asymmetry in rainbow trout may result from an upper limit restricted by directional selection for developmental stability and a lower limit determined by inherent randomness in the developmental process.