Mating system evolution in sperm-heteromorphic Drosophila

In Drosophila species of the obscura group, males exhibit sperm-heteromorph ism, simultaneously producing both long sperm, capable of fertilization, an d short sperm that are not. The production of multiple sperm types calls in to question whether mating system correlates, such as sperm length and numb er trade-offs and female remating behavior, are the same as previously desc ribed in sperm-monomorphic systems. We examine three obscura group species, D. pseudoobscura, D. persimilis, and D. affinis that differ significantly in the lengths of their long fertilizing sperm, to test predictions about t he relationship between sperm length and four mating system characters: mal e age at sexual maturity; sperm number; female remating; and male reproduct ive output. In D. affinis, where males produce the longest fertilizing sper m, their sexual maturity is delayed and they produce fewer long sperm compa red to the other two species, as predicted if long sperm are costly to prod uce. Female D. affinis, although they receive fewer sperm than females of t he other two species, do not remate more frequently or produce fewer progen y from a single mating. Different responses between sperm-heteromorphic and sperm-monomorphic systems underscore the complex nature of the coevolution between male and female mating system characters. (C) 2001 Elsevier Scienc e Ltd. All rights reserved.