Heterozygosity at enzyme loci and morphological variation.

Two recent reports have concerned the relationship between genic heterozygosity, as indicated by electrophoretically detected enzyme loci, and an individual's tendency to depart from the mean on a variety of morphological traits. Using different methods to assess differences in morphological variances between homozygote and heterozygote classes, both conclude that homozygotes show a significantly higher level of morphological variation. These conclusions are important in that they seem to extend the phenomenon from studies on manipulated stocks of organisms to variation in natural populations. As Eanes points out, it is necessary to determine the generality of of this result. Both these studies consider poikilotherm animals (a fish and an insect), so it would be particularly interesting to look for the relationship in homoiotherms. As a contribution to this end, I present here the results (Table 1) of an analysis of variation in the Rufous-collared sparrow, Zonotrichia capensis. I found no difference in levels of variation either between the homozygote and heterozygote classes or between classes of individuals heterozygous at different numbers of loci. My results thus suggest a difference between homoiotherms and poikilotherms in this phenomenon.