Teneral matings in fruit flies: male coercion and female response

Keywords: Drosophila melanogaster forced copulation fruit fly mate choice sexual conflict sexual selection Extensive research indicates that sexually mature female fruit flies typically choose with whom to mate, a process that is crucial for the operation of sexual selection and population divergence via female choice. We followed up on field data suggesting that male fruit flies (Drosophila melanogaster) force copulate with teneral females, which are recently eclosed females characterized by their folded wings and soft, light coloured bodies. Our results indicated that males succeeded in mating with about 20% of the teneral females from our CantonS population and 15% of the teneral females from a local, wild-caught D. melanogaster population. Males were most likely to mate with recently eclosed females and failed to mate with females older than 1 h posteclosion. Close behavioural observations indicated coercion by the males and resistance by the teneral females. The teneral females continued to fight off males throughout copulation and this probably contributed to the shorter mating duration of teneral females relative to that of mature females. Although teneral females failed to foil some forced copulation attempts, they could reduce the impact of such copulations by subsequently remating with a male of their choosing. Indeed, tenerally mated females were six times more likely to remate than were control females that had mated when mature. Our results substantiate a novel aspect of sexual conflict in fruit flies, which could counteract processes driven by female mate choice. Research with fruit flies (D. melanogaster) indicates that the females can choose with whom to mate and otherwise deflect males' persistent advances (Spieth & Ringo 1983). A notable exception is the intriguing report by Markow (2000) indicating that males apparently forced copulation with teneral females in wild populations of D. melanogaster and D. simulans. The males approached teneral females, readily identified by their light colour, soft body and folded wings, and mounted them following either brief courtship or no courtship at all. The teneral females showed no obvious rejection behaviour (Markow 2000). Surprisingly, we know of no follow-up studies elaborating on Markow's (2000) observations in spite of their potential importance. The general topic of sexual conflict has received significant attention (reviewed in: Arnqvist & Rowe 2005; Fricke et al. 2010) and the specific issue of forced copulation has been examined in a variety of taxa (McKinney et al. 1983; Clutton-Brock & Parker 1995; Thornhill & Palmer 2000). Still, there …