Variation in male courtship song traits in Drosophila virilis: the effects of selection and drift on song divergence at the intraspecific level.

Genetic and phenotypic divergence of Drosophila virilis laboratory strains originating from different parts of the species range were studied with the aid of microsatellite markers and by analysing male courtship songs. The strains from America, Europe, continental Asia and Japan showed moderate geographic clustering both at the genetic level and in several traits of the male song. The genetic distances and the song divergence of the strains did not show significant association, which suggests that the songs have not diverged solely as a side-effect of genetic divergence. Comparison of the songs of the laboratory strains to those of freshly collected strains showed that pulse characters of the song are quite sensitive to culture conditions. While laboratory rearing of the flies had no effect on the number of pulses in a pulse train or the pulse train length, the tendency of the sound pulses to become longer during laboratory maintenance could explain the lack of geographic variation in pulse length and inter pulse interval. Sensitivity of songs to culturing conditions should be taken in account in studies on song divergence.

Complex inheritance of male courtship song characters in Drosophila virilis.

We analyzed the inheritance of two male courtship song characters, number of pulses in a pulse train, and length of a pulse train in Drosophila virilis. Biometric analyses of song differences among 16 crosses over three generations (parental and reciprocal F1, F2, and backcrosses) were performed using two different approaches. The joint scaling test revealed significant additive and dominance components, and also significant additive interaction between maternal and progeny genotypes. The direction of dominance was toward shorter and denser pulses in D. virilis. In addition, planned comparisons (contrast analyses of variance) between different generations revealed significant Y chromosomal and transient maternal factors and their interactions, with all other factors contributing to differences in the means of song characters. These results suggest that the genetic basis of courtship song characters in D. virilis is primarily of autosomal polygenic nature, with small but significant Y chromosomal and nonchromosomal maternal effects.

Nucleotide and repeat length variation at the nonA gene of the Drosophila virilis group species and its effects on male courtship song.

Genes found to affect male courtship song characters in Drosophila melanogaster are good candidates when tracing genes responsible for species-specific songs in other Drosophila species. It has previously been shown that Thr-Gly repeat length variation at the period gene affects song traits in D. melanogaster, which gives the repetitive regions a special interest. In this work, we have characterised the patterns of nucleotide variation for gene regions containing two Gly and one Gln-Ala repeat in another D. melanogaster song gene, no-on-transient A, in D. virilis group species. The levels of nucleotide variability in D. virilis nonA were similar to those found for other genes of the species, and the gene sequences showed no signs of deviation from neutrality. The Gly 2 repeat preceding the central domain of the gene exhibited length variation, which did not, however, correlate with song variation either within D. virilis or between the species of D. virilis group. The Gly 3 repeat located on the other side of the central domain showed amino acid divergence parallel to the consensus phylogeny of the D. virilis group species. The species of the virilis subgroup having Asn after the first three glycines in this repeat have simple songs with no species-specificity, while the species of the montana subgroup having two Gly or Asn-Ser in this site have unique courtship songs. Amino acid differences between the species in this repeat may, however, reflect species phylogeny rather than have an effect on song divergence per se.