Courtship songs of Drosophila pseudoobscura and D. persimilis: analysis of variation.

Differences in Drosophila courtship song elements are thought to confer species sexual isolation because of the low levels of variation within species, the large differences often seen between closely related species, and the results of experiments using synthetic songs in two species groups. In this study, we reanalyse the courtship song elements of D. pseudoobscura and D. persimilis. We confirmed the differences between these species in high-rate repetition song interpulse interval (IPI) and intrapulse frequency and in the amount of low-rate repetition song produced. We found that both X-chromosome and autosomal loci contribute to the differences between D. pseudoobscura and D. persimilis in their IPI and intrapulse frequency. No association was detected between IPI and hybrid male mating success to females of either species, although frequency was associated with mating success to D. persimilis females. Additionally, we found evidence of IPI periodicity in the song of D. persimilis, demonstrated differences in mean IPI between D. pseudoobscura populations, and showed a significant influence of temperature on IPI and intrapulse frequency. Such environmental effects may have obscured tests for population differentiation in courtship song parameters in other species, and we suggest the possibility that differences between Drosophila species in mean courtship song IPI might only rarely affect their sexual isolation. Copyright 1998 The Association for the Study of Animal Behaviour.