Parallel Evolution in European and North American Populations of a Geometrid Moth

Abstract

THE phenomenon of industrial melanism in the Lepidoptera has provided an exceptional opportunity for the observation of minor evolutionary changes within relatively short periods of time. Many species of moths, have, in the past 100 years or so, developed melanic forms which have spread and largely replaced the predominantly pale-coloured ‘normal’ forms. Melanic forms first appeared and have reached their greatest relative frequencies in or near centres of heavy industry. Selective predation by birds appears to have contributed toward the decrease in relative frequency of the original pale forms¹. Biston betularia (L.) (Geometridae) is the species which has been most extensively studied in Britain, and since a very similar moth, B. cognataria Guenee, occurs in North America, some comparison of the evolution of melanism can be made. It can be assumed that geographical barriers prevent gene flow between North American and European populations of these moths.