The adaptive role of a species-specific courtship behaviour in coping with remating suppression of mated females

Three-way interactions consisting of a female and her current and previous mates have been studied intensively in the context of sperm competition involving male manipulation of female remating rate but have rarely been documented in a broader context involving classical premating male display and stimulatory traits such as courtship behaviour. This is surprising because premating traits influence the intensity of postmating competition, which occurs only when a mated female consecutively accepts another male. In Drosophila fruit flies, the subsequent male has an advantage over the previous male in sperm competition. However, the ejaculate of the previous male changes the female's behaviour to refuse remating for several days (remating suppression), reducing the potential advantage of the subsequent male. Under such conditions, the evolution of any means that counteract remating suppression is thought to be adaptive for the subsequent male. Males of the fruit fly Drosophila prolongata perform a unique courtship behaviour called ‘leg vibration’. Although leg vibration increases female receptivity, it is not always required for mating with virgin females, raising a question of why it evolved in the first place. In this study, the role of leg vibration in remating was examined, using leg amputation to manipulate the efficiency of leg vibration and an eye colour mutation to detect remating events. Leg vibration had a profound effect on mated females: the remating rate was extremely low with leg-amputated males, indicating that leg vibration was almost indispensable for remating of recently mated females. Our results demonstrated that single courtship behaviour has different levels of importance or necessity for the first male and the subsequent males, providing an example of the evolution of courtship behaviour that was possibly driven by postmating competition.