BUSH-CRICKET SPERMATOPHORES VARY IN ACCORD WITH SPERM COMPETITION AND PARENTAL INVESTMENT THEORY

Sperm competition theory predicts that males will vary the number of sperm ejaculated according to the intensity of competition expected over the fertilization of eggs. Parental investment theory predicts that the magnitude of male investment in offspring should be associated with confidence of paternity. The spermatophores of some bushcrickets serve the dual functions of delivering sperm and providing the female with a nutritious meal that appears to function as parental investment. We show how male Requena verticalis increase the number of sperm in the ampulla of the spermatophore and reduce the amount of spermatophylax material when mating with females with whom they have a low confidence of paternity. These changes in spermatophore morphology are in accord with theories of sperm competition and parental investment.