Flight morphology in fragmented populations of a rare British butterfly, Hesperia comma
Hill JK., Thomas CD., Lewis OT.
In modern landscapes, many populations of rare species are restricted to fragments of formerly extensive habitat. However, the potential for evolutionary changes in dispersal ability to occur within these fragmented populations has received little attention. We examined morphological traits associated with flight and reproduction in fragmented populations of the silver-spotted skipper butterfly, Hesperia comma. Investment in flight was measured as relative wing area and thorax mass, and investment in reproduction as relative abdomen mass. All measurements were made on individuals reared in a common environment. In the UK, Hesperia comma was once fairly widely distributed in southern and eastern England, but retracted to its smallest UK distribution in the 1970s and 1980s. It then partially re-expanded in the North and South Downs in S.E. England. We first compared traits from colonised and refuge sites 2.9-4.5 km apart, and found no differences in relative investment in flight or reproduction. There were, however, significant differences in both relative thorax and abdomen mass between regions > 40 km apart. Populations with the highest relative investment in the thorax occurred in a region where population expansion has been most rapid. These results, in combination with other studies linking butterfly morphology to patch area and/or isolation, suggest that evolutionary responses to habitat fragmentation could be widespread.