Studies of colour polymorphism in some marginal populations of the aposematic jersey tiger moth Callimorpha quadripunctaria

Abstract

Callimorpha quadripunctaria (Lepidoptera, Arctiidae) is both genetically polymorphic for hindwing colour and well protected from predators. Polymorphic populations are, however, only found in the extreme northwest of its extensive distribution in Europe and Asia Minor. Use of a colour analyser confirmed the existence of three reasonably discrete colour classes: bright red, orange and yellow. These could each be subdivided into two further groupings of phenotypes, one of moths of pure colour and the other with a secondary colour. The species is polymorphic in SW England, where it became well established in villages and towns around the Exe estuary in the late 19th century. It now extends about 30 km east and west along the south coast of Devon and up to a similar distance inland along the river valleys. The rate of spread is consistent with the substantial dispersal of up to 500 m detected in a capture-recapture experiment performed at Exeter over the whole flight period in August 1984. This experiment also found no differences in timing of emergence, survivorship or within-habitat movement between the sexes or the colour classes. Males may show a higher rate of emigration than females. The species is polymorphic throughout S Devon. Its stronghold to the west of the Exe basin is characterized by a comparatively uniform morph frequency with 5045% red, 20–40% orange and 10–20% yellow. Yellow moths have their highest frequency in this area, red moths in the east and west and orange to the north. Adult activity is concentrated in the 2–3 h after dusk. Air temperatures of higher than 15°C are probably critical to pairing which involves sex pheromones released by females. This may be an important factor limiting the species' range. Our results suggest that climatic selection pressures involving non-visual differences in fitness account for the geographical variation. The lack of daytime activity of moths in comparison to that found by other workers on Rhodes and which is likely in other warmer climates suggests the hypothesis that expression of the polymorphism is favoured in the marginal populations of NW Europe by a relaxation of the stabilizing influence on the warning coloration exerted by visual predators.