Reproductive behavior of Drosophila melanogaster and D. nigrospiracula in the field and in the laboratory

The reproductive behaviors of two species of fruit fly, Drosophila melanogaster and D. nigros-piracula, were compared in field and laboratory populations. A number of differences were observed in the behavior of the two species in their natural habitats. D. melanogaster, which was observed on citrus, mates at its feeding site, whereas D. nigrospiracula, which is cactiphilic. mates on a non-resource-based male territory adjacent to its feeding site. In both species large male size is important for reproductive success. However, in D. melanogaster smaller males tended to be excluded from the breeding site and were therefore not among the pool of potential mates to which females were exposed. Sex ratios were biased toward females in both species, but the high frequency of female remating in D. nigrospiracula may have provided more mating opportunities for the males of this species. Field observations differed from laboratory observations, and I discuss the importance of these differences for understanding the evolution of Drosophila mating systems. Organisms in natural populations usually exhibit differen-tial reproductive success, because some individuals are more successful in obtaining mates than others. Because differentia