FEMALE MATING PREFERENCE FOR LARGE SIZE IN COELOPA-FRIGIDA (SEAWEED FLY)

Female mating preferences were studied in the seaweed fly, Coelopa frigida. The female acceptance/rejection response to the intial mount by randomly chosen males was scored and male mating success determined by the subsequent production of progeny. The sizes of males and females, as well as their genotypes at the alcohol dehydrogenase (Adh) locus, were determined. Both adult size and the Adh locus are known to be strongly associated with a large chromosomal inversion system. Stepwise multiple regression analyses revealed no association between male mating success and male Adh genotype, but a stong association was found with male size. Female mating preferences appear to exert strong directional selection in favour of large males. There was also an association between female acceptance rate and female Adh genotype, which is likely to be a consequence of inversion karyotype rather than the Adh locus. It is suggested that the discrepancy between the mean size of males in natural populations and the preferred male size indicates that the forces of natural (viability) selection and sexual selection act in opposition.