Behaviour-genetic analysis of lovesongs in desert species of Drosophila.

D. arizonae and D. mojavensis are sibling species with overlapping distributions. There is character displacement for sexual isolation. Speciation may have been completed through reinforcement. Part of the sexual isolation can be explained by female preference for male lovesongs. Within the D. mojavensis cluster of the repleta species group lovesongs always contain pulse song with long inter-pulse intervals (L-IPIs) and generally feature pulse song with short inter-pulse intervals (S-IPIs) giving a bimodal IPI distribution. 'Normal' song is produced by a single wing. D. arizonae and D. mojavensis race B differ significantly in mean S-IPIs but not in mean L-IPIs. Divergent character displacement for mean IPIs is absent. The species do not differ for mean burst duration (MBD). Many pairwise comparisons between stocks show significant differences in mean IPIs and MBDs. Females from a sympatric D. arizonae stock prefer simulated songs with IPIs and bursts characteristic of conspecific males and discriminate against simulated songs with IPIs or bursts resembling a sympatric D. mojavensis stock. Females from the sympatric D. mojavensis stock do not discriminate between simulated songs of the D. arizonae and D. mojavensis stocks. In both species, mean IPIs depend on temperature which accounts for between 50-93% of the variation. MBD depends on temperature in 7/8 stocks. Mean IPIs and MBDs of a sympatric D. arizonae and a sympatric D. mojavensis stock remain distinct over 20°C. For sexually mature sympatric males, mean IPIs do not vary with age for a D. arizonae stock but they shorten with age for a D. mojavensis stock. A reduction in MBD with age was observed for a stock from each species. Song characters of sexually mature males, from a single stock of each species, remain distinct in sympatry. IPIs are probably controlled autosomally between species and influenced by the X-chromosome between D. mojavensis races. The Y chromosome may influence burst length. An D. arizonae stock has a shorter mean copulation duration than a D. mojavensis stock. Acoustical communication plays a more prominent role in the evolution of these species than previously recognised.