To a ring-tailed lemur (Lemur catta), smell is all important, and they not only use their genital secretions to warn rival lemurs not to trespass on their territory, but also to inform each other about their sexual status. Elisabetta Palagi and Leonardo Dapporto wanted to know if lemurs could distinguish the scents of individual females from different groups that compete for territory (p. 2700).
Analysing the chemical components of individual female's scent, the team found that each female's scent had a unique chemical signature, which didn't change over years, seasons, or reproductive cycles. They then showed that both male and female lemurs could tell filter paper soaked with secretions apart from clean paper: the lemurs indicated their preference for the scent-soaked paper by sniffing it for longer. Having shown that each female's scent is unique, and that both sexes can distinguish a female scent, the team tested how lemurs respond to scents from different females. While males did not distinguish between any of the scents tested, females investigated the scent from the more serious territorial rival the longer. Given the choice between a familiar female scent from their own group and an unfamiliar female scent, the females investigated the unfamiliar odour for longer, because they see scents from unfamiliar females as more of a threat.
Replacing the odour of the familiar female with the scent of a female competitor from a rival group, however, caused the females to prefer the competitor's scent over the unfamiliar scent. This is because the rival female is a known competitor for territory, so is a more serious threat than an unknown lemur. In this particular experiment, males likely see all females as potential mates, so investigated all scents equally, while females are sniffing out potential rivals.