Offensive and defensive sperm competition roles in the dung beetle Onthophagus taurus (Coleoptera: Scarabaeidea)

Publication Type:Journal Article
Year of Publication:2006
Authors:C. M. House, Simmons L. W.
Journal:Behavioral Ecology and Sociobiology
Keywords:Defensive role, male genitalia, Offensive role, Onthophagus taurus, Sperm competition

Sperm competition is predicted to generate op- posing selection pressures on males. On one hand, selec- tion should favour ‘defensive’ adaptations that protect a male’s ejaculate from displacement, while, on the other hand, selection should favour ‘offensive’ adaptations that overcome paternity assurance mechanisms of rivals. Here, we use the sterile male technique to assess sperm pre- cedence when a male dung beetle Onthophagus taurus mates in both a defensive (first male) and an offensive (second male) role. Significant variation in a male’s sperm precedence (both P1 and P2) was detected, and an individual’s defensive (P1) and offensive (P2) abilities were positively correlated. Thus, it appears that sexual selection simultaneously selects for ‘defensive’ and ‘of- fensive’ adaptations in O. taurus. We discuss a variety of male traits in O. taurus that potentially contribute to a male’s ability to be successful whenmatinginan‘of-fensive’ and a ‘defensive’ role.

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