Non-random mating in natural populations of the seaweed fly, coelopa frigida

Abstract

Experiments are reported that were designed to test for the randomness of mating in seaweed flies (Coelopa frigida) with respect to size, to genotypes at the alcohol dehydrogenase (Adh) locus, and to a chromosomal inversion with which the Adh locus is associated. Mating was allowed to occur in samples of wild animals, and the females then individually invited to lay eggs. By determining the genotypes of the mother and her progeny, the father’s genotype could be inferred. The observed distribution of matings was then compared with expectations assuming random mating. It was found that animals mated in a positively assortative fashion with respect to their size, but disa$sortatively with respect to the Adh locus and the α/β inversion on chromosome I. Large females tended to mate with large males, but not with males of their own Adh genotype. Mechanisms that might give rise to this pattern of non-randomness are discussed. The consequences of disassortment are that it would be expected to contribute to the maintenance of genetic variation. © 1987 The Genetical Society of Great Britain.