Coat darkness is associated with social dominance and mating behaviour in a mountain sheep hybrid lineage

Natural hybridization can produce novel traits when morphologically different populations hybridize, and can introduce variation in traits that become associated with sexual selection. Evidence from breeding experiments and genetic markers indicate that the great variation in coat darkness and the unique coat patterns found in Stone's sheep Ovis dalli stonei, populations, have resulted from an ancient hybridization event between thinhorn sheep, O. dalli, and bighorn sheep, O. canadensis. Behavioural evidence gathered in 2003 and 2004 in Yukon Territory, Canada, showed that higher dominance rank was correlated with increasing darkness in rams, and comparatively darker rams were seen more often tending oestrous ewes. The relationship between ram darkness and dominance and use of the tending mating tactic was still significant after age or horn size were controlled. In sum, our study demonstrates an interesting example of the potential for hybridization to generate diversity. In the case of mountain sheep an ancestral hybridization has resulted in a subspecies with unique coat colour characteristics that are associated with social dominance and mating behaviour.