Postcopulatory sexual selection in Mediterranean fruit flies: advantages for large and protein-fed males

Previous laboratory studies of Mediterranean fruit flies, Ceratitis capitat a (medflies), have identified large size and protein feeding as positive in fluences on the ability of males to secure copulations. In this study, we i nvestigated whether large and protein-fed males experience additional advan tages in terms of amount and distribution of sperm stored by mates. We also examined relationships between copula duration and sperm storage. Mates of large and protein-fed males were more likely to store sperm and to store m ore sperm than mates of small and protein-deprived males. Probability of sp erm storage was associated with copula duration; all copulations lasting le ss than 100 min failed whereas 98% lasting longer than 100 min succeeded. C opulations involving sperm storage were longer if males were small or prote in deprived or if the female was large, although there was no evidence of a relationship between copula duration and total sperm storage. Evidence fro m related studies suggests that variation in latency until sperm transfer, caused by size and diet, is a likely explanation for varying copula duratio n. Sperm tended to be stored asymmetrically between the female's two sperma thecae, consistent with a mating system in which females maintain isolated populations of sperm from different males and later select between them. St orage was less asymmetric when large numbers of sperm were stored but there was little evidence that male size or diet affected this asymmetry. It is uncertain whether postcopulatory advantages of large and protein-fed male m edflies arise from female preferences or male dominance through coercion or force. (C) 1999 The Association for the Study of Animal Behaviour.