Secondary sexual characters in crawling water beetles (Coleoptera: Haliplidae): evidence for sexual conflict?

Abstract

Conflict between sexes occurs as a result of asymmetric reproductive trade-offs during mating. When the rates of these trade-offs differ, sexual conflict can occur, this can lead to coevolutionary arms races between the sexes. Such arms races may result in the evolution of secondary sexual characteristics and the coevolution of sex related structures. This study analysed the morphology of three genera of Haliplidae: Haliplus, Brychius and Algophilus using Scanning Electron Microscopy to determine whether there was evidence of sexual conflict. Males in this family possess small tarsal suckers on the fore and mid-legs that aid the male to grasp the female’s dorsal surface during mating, potentially increasing reproductive success. Females also possess micropunctation on the dorsal surface which may deter male attachment. This study investigates the notion of female evolution of sex related counteradaptations that reduce potentially costly copulations. Results from this study indicate that there is little covariance in secondary sexual characters between the sexes this family as a whole (P = 0.934, r = -0.030). However, there was significant evidence of differentiation in sex-specific characters amongst certain species, inferring that characters may be evolving phylogenetically. Further investigation into specific clades of Haliplidae would be beneficial, as an equivalent comparison can be made between sexes of the same clade.