Sexual dimorphism and courtship behavior in Drosophila prolongata

Abstract

Sexual dimorphism is often derived from sexual selection. In sexually dimorphic Drosophila species, exaggerated male structures are used for specific behaviors in male-to-male competition or courtship toward females. In Drosophila prolongata, a member of the melanogaster species group, males have enlarged forelegs whereas females do not. However, the adaptive role of the enlarged forelegs is unclear because little is known about the behavior of D. prolongata. In this study, the courtship behavior of D. prolongata was investigated in comparison with closely related species. Males of D. prolongata use their forelegs in a specific behavior, ''leg vibration'', in which the male vigorously vibrates the female's abdomen by extending his forelegs from in front of her. Leg vibration was observed immediately before ''attempting copulation'', indicating that it has an adaptive role in the mating process. In contrast, leg vibration was not observed in closely related species. Because the large forelegs are necessary to accomplish leg vibration, it was suggested that the sexual dimorphism of D. prolongata forelegs is currently under the influence of sexual selection in courtship behavior.

Social context-dependent modification of courtship behaviour in Drosophila prolongata

“…However, successful copulations were not always preceded by leg vibration [16,19], suggesting that males of D. prolongata have alternative courtship sequences. As courtship behaviour was observed from above in the previous studies [16,19], some behavioural elements may have been out of view. We re-examined the courtship sequence by closer observations from the side as follows: a male and a female were introduced into a vial (25 mm diameter  100 mm height) containing cornmeal medium.…”

“…Therefore, we used multiple strains of known behavioural characteristics to ascertain the robustness of the results. BaVi044 was used in a previous study as the standard strain for the analysis of courtship sequence [16]. BaVi043 and SaPa014 were strains with high and low leg vibration rate, respectively [19].…”

“…Although leg vibration was suggested to stimulate females to accept copulation [16], its function had not been proved experimentally. We examined the effect of leg vibration on female receptivity by the following two observations.…”

“…Drosophila prolongata is a fruit fly that shows prominent sexual dimorphism in its forelegs [16][17][18]. When courting females, males perform 'leg vibration', in which a male vibrates the female's abdomen from in front of her using his enlarged forelegs [16].…”

“…When courting females, males perform 'leg vibration', in which a male vibrates the female's abdomen from in front of her using his enlarged forelegs [16]. The functional relationship between leg vibration and the enlarged forelegs suggests that this courtship behaviour has played an important role in the evolution of foreleg morphology.…”