Some show it with a love song. Others may show it with a wedding ring. But in lemur lovers, the strength of their union is marked by the similarity of their smells. Scientists at Duke University, North Carolina, studied the behaviour of six pairs of Coquerel’s sifakas before, during and after they mated. They also looked at the chemical makeup of the sifakas’ scent marks – the sticky goo that both sexes dab on their surroundings when courting. Before reproducing, sifakas spend a lot of their time leaving these scents on tree branches, while also investigating their partners’ scents. After mating, their scents become more similar to each other.
“It’s like singing a duet,” said Christine Drea, who led the study, “but with smells instead of sounds.” Coquerel’s sifakas are one of many endangered lemur species found only in Madagascar. The behaviour of lemurs – particularly that of social species – has been the subject of many studies, in part owing to their female-dominant social structure, which is rare among primates. As well as starting to smell like their partners, lemur pairs begin to mirror each other’s marking behaviour as they become familiar with one another.
“When one member of a pair started sniffing and scent-marking more often, their mate did too,” said Lydia Greene, who collected the data. She and Drea describe this as a “getting-to-know-you mechanism during the period of bond formation.” Greene thinks scent marking may also be a way for the males to work out when it’s time to mate. She said: “If two animals have never reproduced, the male doesn’t necessarily know what the female smells like when she’s in heat, because they’ve never gone through this before.” Interestingly, although the similarity of partners’ scent profiles is a good measure of their strength as a reproducing couple, the length of their time living together before mating has no effect on their scent similarity or later reproductive success.
The next step will be to look at how sifakas’ chemical signals compare with those of some other lemurs where social behaviour has evolved independently. This could help determine the purpose of these chemical messages. One possibility is that they advertise couples’ bonds, much like in some bird pairs, where vocal signals become similar.
“[They could be saying] we’re a thing,” suggests Greene. “We’ve bonded. Don’t mess with us.”