Relative influence of male and female genital morphology on paternity in the dung beetle Onthophagus taurus

Studies of fertilization success have demonstrated that male effects are often a strong and important source of variation in P₂ (the proportion of offspring that are fertilized by the second male to mate). More recently there has been emphasis on female processes that occur during and after copulation that might bias the outcome of male-male interactions. Here we used the sterile male technique to evaluate whether female genital morphology influences the repeatability of P₂ when the same pair of male dung beetles, Onthophagus taurus, copulated with a series of full-sib females or unrelated females that were all unrelated to the male pair. Repeatability estimates of measures of female genital morphology showed that full-sib females varied less in their genital morphology than did unrelated females. Therefore, if female genital traits are an important source of variation in male fertilization success, P₂ should be more repeatable across full-sib than unrelated females. Contrary to this prediction, we show that the repeatability of P₂ did not differ between female groups. Moreover, specific dimensions of the female genitalia (sclerotized vagina and bursa) did not contribute significantly to variance in P₂. In contrast, male effects had consistent and repeatable influences on paternity across females. These were partly explained by variation in the morphology of male genital sclerites.