Artificial selection for a courtship signal in Drosophila melanogaster

The mean inter-pulse interval of the song of male Drosophila melanogaster is a courtship signal which shows relatively little variability in natural populations and is important to male mating success. Artificial selection was carried out on this trait for six generations, producing a line of flies that had a mean inter-pulse interval outside the normal range for the species. The stock used was derived from isofemale lines taken from a natural population in which other studies had suggested heritability for this trait was low. The response to selection was asymmetric, with a greater response for longer inter-pulse interval. Analysis of other changes between the lines suggests that the genes selected for act fairly specifically on inter-pulse interval, reducing both the mean inter-pulse interval and the number of pulses produced. Analysis of F₂ and back-cross generations suggested a polygenic additive architecture without a significant non- additive component or disproportionate role of sex-linked genes on mean inter-pulse interval. Contrary to expectations, variance was greater in the F₁ than in F₂ or back-cross generations, and the realized heritability was much greater than the evolvability (coefficient of additive genetic variation). The results suggest that behavioural traits with low variability still retain the potential for rapid evolution, perhaps because environmental sources of variation counteract fixation.