Body size and male reproductive performance in the flesh fly, Neobellieria bullata

The number of sperm contained in virgin male flesh flies ( Neobellieria (= Sarcophaga) bullata) is strongly influenced by their size and age. Furthermore, the number of sperm transferred to females during copulation is positively correlated with male body weight. Sperm number in male flies is related to size by the equation: ln sperm number=9.24 + 0.675 ln male weight (mg). Virgin male flies held without access to females continue to produce sperm at a linear rate during the first 16 days of their lives. On average males produce 19,637 sperm per day, however, larger flies produce sperm at a greater rate than smaller flies; males ranging in size from 15 to 36 mg produced 17,800 ± 1899 sperm per day whereas males ranging in size from 50 to 76 mg produce 27,036 ± 2803 sperm per day. Males transfer an average of 6965 ± 712 sperm in copulations lasting 165 ± 15 min. The number of sperm transferred was significantly correlated with body size whereas mating duration was not. These results clearly document the relationship between body size and male reproductive performance and complement a large body of work relating body size to reproductive performance in females.