Developmental stability and enzyme heterozygosity in rainbow trout.

The developmental pathways of organisms are genetically adjusted to produce the characteristic morphology of the species regardless of variations in internal and external conditions during development. This 'developmental buffering', however, is not always precise. Bilateral characters of an organism are often asymmetric, that is, different in size, shape or number. Fluctuating asymmetry occurs when the difference between a character on the left and right sides of individuals is normally distributed about a mean of zero. This type of asymmetry results from the inability of an organism to develop precisely along determined paths and can be used as a measure of developmental stability. Increased developmental stability would be reflected by reduced amounts of fluctuating asymmetry. We have now examined the relationship between the amount of fluctuating asymmetry for five bilateral characters and heterozygosity at 13 polymorphic loci in a population of rainbow trout (Salmo gairdneri). Our results indicate a significant negative correlation between the proportion of heterozygous loci and the proportion of asymmetric characters. These data provide evidence that individuals with greater heterozygosity within a population have increased developmental stability.