Hybrid Zones and Sexual Selection 503 HYBRID ZONES AND SEXUAL SELECTION: INSIGHTS FROM THE AWASH BABOON HYBRID ZONE (Papio hamadryas anubis x P. h. hamadryas)

INTRODUCTION Ever since the idea was first espoused by Darwin in his classic The Descent of Man and Selection in Relation to Sex [Darwin, 1871], the evolutionary importance of sexual selection has been documented within a multitude of species. Comparatively few studies, however, have focused on the impact of sexual selection on populations of naturally occurring hybrid animals, or hybrid zones, particularly among highly social animals such as primates. Sexual selection is potentially very important in hybrid zones for two complementary reasons. First, hybrid zones typically have high levels of variation in both potential mates and competitors for those mates. This provides unique opportunities to observe sexual selection (both mate choice and within-sex competition) and can reveal relationships that might be too subtle to detect over the range of variation found within a single species. Second, the consequences of sexual selection in hybrid zones can have profound impacts for the evolutionary tra-jectories of the hybridizing taxa. For example, the evolution of mate preference for conspecifics in the face of selection against hybrids may ultimately lead to speciation, Conversely, mate preference for unusual or migrant animals could increase gene flow between the two populations, causing what otherwise might have been "good" species to merge. Asymmetry between hybridizing taxa in ability to compete for mates can have similar consequences This chapter presents data on mate preference and intrasexual competition from hybrid baboons (Papio hamadryas ha-madryas x P. h. anubis) located in Ethiopia's Awash National Park as an example of sexual selection and its consequences in primate hybrid zones.