INTRASPECIFIC VARIATION IN SPERM COMPETITION SUCCESS IN THE BULB MITE- A ROLE FOR SPERM SIZE

Success ill sperm competition is one of the principal determinants of male fitness in species in which females mate promiscuously, but the s elective pressures it causes are only partly understood, especially wi th respect to sperm characteristics favoured under sperm competition. Correlates of male success in sperm competition were examined in the b ulb mite (Rhizoglyphus robini). The effects of the characteristics of individual male's ejaculates (sperm size and number), their body size and copulation duration were examined. Only sperm size was significant ly correlated with sperm competition success: males producing larger s perm wer more successful. Moreover, ejaculates of males producing larg er sperm also had significantly smaller variation in sperm size, which indicates that they were able not only to allocate more resources to sperm but also to maintain more stable allocation per gamete. There wa s no significant correlation between sperm size and number of sperm pe r ejaculate.