Effect of larval crowding on adult mating behaviour in Drosophila melanogaster.

The effect of larval density on male mating success has been investigated with two strains of Drosophila melanogaster, a wild strain and a mutant strain, under low and high larval competition, and four different genotypic frequencies. The results show a strong sexual selection against mutant males when flies have been raised under low larval competition. Under high larval competition, there is a reduction in mating disadvantage of mutant males. In both instances, a frequency-dependent sexual selection exists. These results explain adequately the evolution of experimental populations where egg to adult viability and male mating success are the most important components of fitness.