Sexual selection in dung beetles. I. A multivariate study of the morphological variation in two species of Onthophagus (Scarabaeidae: Onthophagini)

Sexual dimorphism in horned beetles reflects a history of different selection pressures operating on males and females. A multivariate morphometric analysis was carried out on two scarabaeine dung beetles, Onthophagus binodis Thunberg and 0. ferox Harold. There is clear structural polymorphism within 0. binodis; horned males, females and hornless males were separated on the basis of body shape. Sexual dimorphism within 0. ferox was established; sexes were separated according to the size of pronotal and cephalic horns. The effect of differential selection is discussed within the context of sexual selection.