Dimorphism in the hartebeest

Sexual selection often favours sexual size dimorphism (SSD) in body size and fighting structures, since large males with massive weaponry achieve high reproductive success. However, sexual selection may be opposed by natural selection. This chapter describes a test of this hypothesis based on comparisons of sexual dimorphism, mating systems (sexual selection), and environmental variables (natural selection) among subspecies of hartebeest - a group of African savannah antelopes. The potential for polygyny explains dimorphism in fighting structures across hartebeest subspecies although it does not predict dimorphism in body size, suggesting that sexual selection toward large dimorphism is opposed by natural selection for smaller size. In addition to sexual selection, SSD in hartebeest may be influenced by antipredator advantages of small and agile males, intra-sexual competition for food and/or mates among female hartebeest, and fecundity selection.