Characterization of novel microsatellites from Drosophila transversa.

We investigated a partial genomic library of Drosophila transversa for microsatellites and developed 12 markers for genetic analyses. This is the first time that microsatellite primers from the quinaria species group have been described. Four loci were cross-amplified in D. phalerata. Nine out of the 12 microsatellite markers developed are likely to be on the X chromosome.

Genetic analysis of cuticular hydrocarbons and their effect on courtship in Drosophila virilis and D. lummei.

Genetical factors controlling the cuticular hydrocarbons (CHC) of Drosophila virilis and D. lummei, and the effect of CHC on female attractivity were studied. A strong sexual dimorphism was found in D. virilis where (Z)-10-heneicosene and (Z)-11-pentacosene were major CHC for males and females, respectively. In D. lummei, (Z)-9-pentacosene was the major CHC for both sexes. These CHC are under a complex genetical control: the level of male (Z)-10-heneicosene was mainly sex-linked; chromosome 2 exerted a marked hypermorphic effect on it as well as on female (Z)-11-pentacosene; other autosomes had additional smaller effects on the CHC. Further, these two species showed differences in the double bond position pattern: Monoenes, with double bonds in (Z)-11 or (Z)-13, were more abundant in D. virilis (monoenes-vi), while monoenes, with double bonds in (Z)-7 or (Z)-9, were more abundant in D. lummei (monoenes-lu). In agreement with previous studies of perfumed dummies, experiments with live females showed that a higher proportion of (Z)-11-pentacosene or of monoenes-vi induced D. virilis males to court sooner. On the other hand, monoenes-lu showed antagonistic effects.

The role of male courtship song in species recognition in Drosophila montana.

In many Drosophila species the male courtship song is an essential part of a successful courtship, playing a role in species-recognition and/or in sexual selection exercised by the females on conspecific males. In Drosophila montana, specific traits of the courtship song (the length and the carrier frequency of sound pulses) have earlier been shown to play an important role in intraspecific mate choice. Here we show that the male song (especially the interpulse interval) also plays a role in species-recognition, maintaining sexual isolation between sympatric species. We succeeded in breaking down sexual isolation between D. montana females and D. lummei males by playing the females simulated courtship song with a species-specific interpulse interval while they were courted by a mute (wingless) male. Involvement of different song traits in intra- and interspecific mate choice suggests that the song may be affected by both directional and stabilizing selection.

Variability and evolvability of male song characters in Drosophila montana populations.

In Drosophila montana, the male courtship song (especially the pulse characters of the song) plays an important role in sexual selection. The heritabilities and the amount of additive and residual variation in different characters of the male song were measured in two populations using father-son regression and sib analysis. The songs of the males from the Oulanka population were recorded for a second time after the males had been kept in 4 degrees C for 6 months. Heritabilities measured for different song traits were non-significant in each case, largely due to high residual variation. During the cold treatment, the additive variation increased and the residual variation decreased in nearly all song traits. Our results suggest that genotype-environment interactions may increase the amount of additive variation between males in sexually selected song traits during overwintering, prior to the mating season of the flies.

Songs produced by the females of the Drosophila virilis group of species.

Females of the Drosophila virilis group of species may vibrate their wings during courtship producing songs consisting of trains of successive sound pulses (pulse song) or sinusoidal hums (sine song). In the present study we describe these songs and study their role in courtship using a transition analysis. To find out which songs should be classified as pulse songs and which ones as sine songs, we studied the inheritance of different song types in interspecific F1 hybrids. In only a few species did the females produce large quantities of song in successful courtships. The males' reactions to female songs varied from licking and singing to stopping the courtship. Pulse trains with short and long intervals between successive pulses appeared to be different forms of the pulse song, while sine song (sinusoidal hums) was inherited independently of the pulse song.

Secondary courtship songs and inhibitory songs of Drosophila virilis-group males.

The males of all Drosophila virilis-group species produce primary courtship song; and the males of four of these species also provide secondary courtship song when courting a female. The amount of secondary song and the courtship phase at which it is produced vary according to the species. D. lummei males produce secondary song consisting of successive 12-ms-long sound pulses with 70-ms-long intervals between pulses. D. borealis males produce short and dense pulse trains and D. littoralis and D. flavomontana males produce single sound pulses of a long duration (80-160 ms). The males of all species produce pulse-structured inhibitory song when they are courted by another male. In the secondary and inhibitory songs of interspecific hybrids, short and dense pulse trains of parent species break into pulse song with long interpulse intervals. This suggests that songs consisting of short and dense pulse trains and pulse songs with long interpulse intervals are just different modes of the same song. Sine songs (long sound pulses) seem to be inherited independently of pulse song.