Marion Petrie¹ & Phoebe Barnard²

Petrie, M. & Barnard, P. 1999. Sexual selection. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban: 1088. Johannesburg: BirdLife South Africa.

The aim of this symposium is to consider the possible relationship between sexual selection and speciation. In birds, speciose clades are those with a high frequency of sexually dichromatic species. Sexual dichromatism is thought to be an indicator of sexual selection and thus sexual selection is implicated as an agent of speciation. However, how sexual selection can result in speciation is unclear. All of the speakers in this symposium consider different aspects of the problem. Our first speaker, Andrew Pomiankowski, using theoretical considerations suggests that divergence between populations in female preferences may be sufficient to cause speciation, but this depends critically on the assumption that there are no benefits to female choice. Sexual selection, where females gain genetic benefits for their offspring, is thought to result in the removal of genetic variation however, Ben Sheldon, considers how genetic variation in traits undergoing directional selection may be maintained by environmental variation. Ian Jones discovers that recently diverged species of auklets have more elaborate ornaments than older species which stresses the importance of sexual selection in the adaptive radiation of the auklets. Whilst Jacob Höglund stresses the plasticity of life history traits in the Tetraoninae (forest grouse) which can give rise to rapid evolutionary change. Finally, Ian Owens using comparative analyses suggests that interspecific variation in plumage colour in birds arises through the interaction between the signalling environment, crypsis and sexual selection rather than by a mechanism where sympatry results in species isolating mechanisms.