Morphological variance and enzyme heterozygpsity in the monarch butterfly

Abstract

IT was shown several decades ago that the reduction in genetic heterozygosity produced by inbreeding in domesticated plants and animals is accompanied by an increase in morphological variability1,2. While studies of laboratory populations and results of plant and animal breeding have been instrumental in identifying the relationship between genetic heterozygosity and morphological variability, such investigations often involved substantial changes in genetic heterozygosity, such as are produced when entire chromosomes are made homozygous. For this reason their relevance to the levels of heterozygosity in natural populations is unclear. Until recently attempts to examine this relationship in natural populations were hindered by the inability to routinely estimate levels of genetic heterozygosity in nature. However, determinations of genetic heterozygosity at specific enzyme-loci can now be made by electrophoresis. Recently Mitton3 found that heterozygotes for a set of five enzyme-loci had reduced multivariate variances for a set of morphological characters when compared to homozygotes at the same loci in populations of the killifish, Fundulus heteroclitus. It is very important to determine the generality of this observation for other species populations. I have now examined the relationship between genetic heterozygosity, as identified by electrophoresis, and the variance of morphological characters in the monarch butterfly, Danaus plexippus. Study of six polymorphic enzyme-loci in the monarch shows that once again heterozygotes have smaller variances for morphological characters when compared to homozygotes at the same locus.