Multivariate analysis of variation within the Insularia complex of the moth Biston betularia

Abstract

A multivariate analysis of the colour variation of the moth Biston betularia has been carried out. Previous workers have demonstrated that the black form, carbonaria, and the intermediate form, insularia, are controlled by alleles at the same locus. The results of the present analysis of the variation of the insularia phenotype in different populations and in 20 families show that there are at least three distinct insularia morphs and suggest that these are controlled by three different insularia alleles. There is evidence that the allele, which in the heterozygous state produces the palest insularia form, is incompletely dominant. For this reason an objective means of classification, considering several different variables, is required to distinguish the three insularia forms. The scoring method that was devised was used to classify insularia in samples from south Wales. In this area the darkest insularia morph reaches its highest frequencies in urban areas.