Male crickets increase sperm number in relation to competition and female size

There is evidence to suggest that males of various species can respond to the threat of sperm competition by varying the amount of sperm transferred during copulation. We tested this in two species of cricket, Acheta domesticus and Gryllodes supplicans (Orthoptera: Gryllidae) by varying the apparent threat of intermale competition experimentally. The results showed that males of both species increased the amount of sperm transferred as apparent competition increased and that male A. domesticus transferred more sperm when encountering larger females. The results also showed that male G. supplicans produced a larger spermatophylax when a larger ampulla was transferred, a relationship consistent with a sperm protection function. Received: 5 May 1995/Accepted after revision: 27 January 1996