EFFECT OF TEMPERATURE ON THE EXPRESSION OF THE MEDIONIGRA PHENOTYPE OF THE MOTH PANAXIA-DOMINULA (LEPIDOPTERA, ARCTIIDAE)

The well-known medionigra polymorphism in the scarlet tiger moth, Pana xia dominula, occupies an unique position in the history of ecological genetics. Year to year changes in phenotype frequency at the Cothill (Oxfordshire) colony were too great to be explained by random genetic drift, and were used as evidence for selection in a prolonged and heat ed debate between, on one side, E. B. Ford and R. A. Fisher, and on th e other, Sewall Wright. Here we report experiments which clearly demon strate that expression at the medionigra locus is largely determined b y temperature. Since the genotype is not necessarily recognisable from the phenotype, the long series of field scored samples from Cothill d o not accurately record changes in the medionigra allele frequency fro m year to year. Hence interpretation of the data as evidence for selec tion is invalid.