The cost of being able to fly: a study of wing polymorphism in two species of crickets

Summary

The widespread occurrence of wing polymorphisms in insects suggests that the possession of wings and ability to fly adversely affect components of the insect's life characteristics that contribute to its Darwinian fitness. This hypothesis was tested by an analysis of the differences in life history parameters of the macropterous and micropterous morphs of the two cricket species G. firmus and A. fasciatus. In both species there were no differences in development time or adult survival between the two morphs. Significant differences in head width were not consistent between the two species but in both sexes of G. firmus and females of A. fasciatus (insufficient males for analysis) long-winged individuals weighed more than short-winged individuals with the same head width. In both species egg production is delayed in macropterous females. The cumulative fecundity of the micropterous morph is greater than the macropterous morph in both species but only in G. firmus is the difference statistically significant. A. fasciatus frequently loose their wings but no such loss has been observed in G. firmus. There is a significant increase in egg production after the loss of the wings. These results are in accord with those of Tanaka (1976) for the cricket, Pteronemobius taprobanensis.

Breeding experiments indicate that in G. firmus the wing polymorphism is under genetic control. The decrease in fecundity is sufficiently large that genotypes producing only macropterous offspring could only persist in highly unstable environments where continuous dispersal was imperative for survival. However, the reproductive cost of a genotype producing a small percentage of macropterous individuals is slight. The fitness that accrues to a genotype producing a few dispersing offspring is likely to offset the small reproductive cost and hence wing polymorphisms should be favoured.