Female Reseptivity, Song Requirement and Preferences in Drosophila Virilis and D. Montana

Most models of sexual selection focus on coevolution of male sexual trait and female preference for the trait. However, whether the female preference modifies the male trait depends on the overall receptivity of females, on the importance of the male trait for the females, on female sampling behaviour, and on female control over copulation decision. These aspects are often neglected by theoreticians. Female receptivity, song requirement and preferences were studied in two Drosophila virilis group species, D. montana and D. virilis. The main object of the study was female acceptance/rejection behaviour. Female wing spreading posture was a signal for males to attempt copulation, when the female was ready to mate. I used this signal as an indicator of female acceptance. D. virilis females were generally very receptive, but there were differences between females both in receptivity and in responsiveness of the females to simulated courtship songs. D. virilis female did not require song and had a low acceptance threshold with a heterospecific male. These two traits are explained by a high female receptivity. D. montana females, on the contrary, had a high acceptance threshold. These females accepted the courting male only after hearing his song. They also repelled males, which attempted copulation without female acceptance signal. In this species the strength of species discrimination did not correlate with the overall receptivity of the females. Between species hybrid females (from a cross vir x mo and from backcross to mo) resembled D. montana females in their song requirement, but not in their receptivity. This suggests that these two traits are inherited independently. D. montana and D. littoralis females have previously been found to prefer males with short and dense sound pulses in wild. These song characters were repeatable among overwintered males in a fashion different from other song characters. This shows that song characters involved in sexual selection are more sensitive to environmental factors than other song traits.