Genetic variability of courtship song in a population of Drosophila melanogaster

The courtship song of male Drosophila melanogaster influences mating success and may have been involved in speciation within the melanogaster subgroup. The variability of two important parameters of this song, inter-pulse interval and hum-song frequency, within a large recent collection from a wild population, was examined. The phenotypic variability was low (coefficients of variation were 5·4 and 7·7%, respectively). Although there were indications of variability among males and families, the heritability of both parameters measured by father-son regression was not significant. Twenty isofemale lines from the same population were also examined after 30 generations of culture in the laboratory. These showed similar phenotypic variability, although a greater proportion of this was among families. A single generation of artificial selection showed that this variation included a genetic component which responded to selection. Reasons for the discrepancy between the results of the two studies are discussed. It is concluded that D. melanogaster song shows relatively low phenotypic and additive genetic variability, which is consistent with most expectations for an important mating signal. However, the character can evolve following genetic drift, probably because of non-additive sources of genetic variation in the original population.