Interactions between males and their sperm during multi-male copulatory episodes of deer mice ( Peromyscus maniculatus)

Abstract

Twenty triads of one female and two male deer mice, Peromyscus maniculatus bairdi, copulated in tests in which the dynamics of male-male interactions and sperm competition could be analysed. Paternity of offspring was determined with starch-gel electrophoresis. Basic parameters of male copulatory behaviour resembled those of one-male, one-female episodes. Male-male influences on copulatoon were subtle and complex, with a given male somewhat less likely to copulate during the other's copulatory than refractory periods. Males ejaculating first or last gained no reproductive advantage. The male attaining more ejaculations sired more, but not significantly more, offspring than the other male. However, the predictability of litter composition was improved and significant when ejaculations followed by a female post-ejaculatory quiescent period of 1 min or less were discounted. This suggests that male deer mice can essentially cancel the ejaculation of another male by copulating within 1 min of his ejaculation.