The evolution of female weaponry

[Truncated abstract] The evolutionary importance of secondary sexual traits in enhancing reproductive success amongst males has long been recognised. Empirical support for the function of male armaments and ornaments in inter and intrasexual competition is vast. However, there are a number of species in which females also exhibit secondary sexual characteristics, and this phenomenon still remains poorly understood. A better understanding of the potential selective pressures operating to favour the evolution of armaments and ornaments in females is required and necessary to re-address the imbalance of sexual selection studies that focus solely on sexual selection on males. This thesis addresses this gap in knowledge by exploring secondary sexual trait evolution in females by investigating the presence and influence of sexual selection on the evolution of horns in females of the dung beetle species, Onthophagus sagittarius. Chapter 1 introduces the subject area with a review of the literature relevant to the topic of secondary sexual traits in females and discusses the factors that have the potential to contribute to their evolution. The following chapters each deal with a specific aspect of the topic in turn. Chapter 2 investigates whether the sex-specific horns of O. sagittarius are under inter-sexual selection pressures operating via male mate choice. I found no direct evidence of male mate choice operating on female horns, but strong evidence for female preferences for large males exhibiting high courtship rates. I also found evidence to suggest that females differentially allocate reproductive investment to offspring sired by particular males. Thus my findings show that O. sagittarius has a conventional mating system with regard to mate choice, and females horns are unlikely to have evolved as ornaments.