Wing-beat frequency mutants and courtship behavior in Drosophila melanogaster males

Flightless mutations that affect wing-beat frequency (WBF) of Drosophila melanogaster were examined for their effect on male courtship. WBFs were measured using a fixed-wire tether that completely supports the fly in an attitude similar to hovering flight. The two spontaneous mutations, one of which reduces WBF to one-half normal and the other to zero, were placed on an isogenic background and were compared to an isogenic wildtype strain and to a genetically heterogeneous wildtype strain. Time to mating under noncompetitive conditions (single pair matings) was not significantly different among the four male types in one experiment. In a second experiment, although the time to mating varied significantly among the four male types, there was no association between the WBF that was characteristic of a male type and the length of time to mating. Time to mating was not significantly correlated with WBF, wing size, or body mass in either experiment. Genetically heterogeneous wild-type females were significantly more receptive (had shorter times to mating) than inbred wild-type females toward all four male types. During the time-to-mating tests, all four male types appeared to show typical courtship behaviors. Therefore, the male types were compared for possible differences in four components of the male courtship song: sine song frequency, interpulse interval, intrapulse frequency (= carrier frequency), and wing cycles per pulse. One or another of these components showed significant differences among the four male types (e.g., genetically heterogeneous, wild-type males showed a significantly higher sine song frequency and intrapulse frequency than males of the three isogenic types). However, the average values for all four male types were within reported wild-type ranges for each courtship song component. Although the two mutations drastically reduce WBF during tethered flight, they do not have any similar major effect on courtship. Apparently they affect muscles or neuronal control mechanisms that are not common elements shared by the wing movement of flight and male courtship song.