Older males have higher insemination success in a beetle

Abstract

The hypothesis that male age affects insemination success was tested in a field study of a fungus beetle, Bolitotherus cornutus. In this species, male competition is important in determining the number of females with which a male attempts to copulate, but females have control over whether an attempt results in sperm transfer. Thus the proportion of a male's copulatory attempts that are accepted by females is a measure of the male's insemination success, independent of his overall access to females. This proportion was found to increase significantly as a male ages; thus, older males had higher insemination success. The insemination advantage of older males could be the result of two different mechanisms: female choice of older males or greater access of older males to highly receptive females. Neither of these mechanisms could be definitely supported or refuted based on the data collected in this study; therefore, further studies are necessary to determine whether one or both of these non-mutually exclusive mechanisms account for the older male advantage.