Long-term studies of the Medionigra polymorphism in the moth Panaxia dominula: a critique

Monitoring of the medionigra polymorphism in the moth, Panaxia dominula, at Cothill, Oxfordshire, UK, provides one of the longest and most complete data series in ecological genetics, and has provided a cornerstone in the development of this discipline. Changes in frequency between generations were used as proof of the overriding importance of selection in the prolonged and often heated selection/drift debate between R. A. Fisher, E. B. Ford and Sewall Wright. Recently evidence has emerged which suggests that the study may be flawed, particularly since phenotype appears to be influenced by environment. We offer what we regard as a proof of the inadequacy of this polymorphism for demonstrating selection, since phenotype is largely determined by temperature during the late larval or pupal phase. Hence workers at Cothill were not recording genetic processes. Assumptions that the medionigra form occurred only at Cothill, and that gene flow never occurred between Cothill and neighbouring populations, also appear to be untrue. The long-term study at Cothill may remain as a landmark in the history of ecological genetics only by virtue of the cautionary lessons it may teach future workers in this field.