Zanna Clay
Photo of female bonobo named  Isiro. During interactions with higher-ranked female partners, females produce copulation calls to advertise their socio-sexual interactions.
updated 3/1/2012 12:08:44 PM ET 2012-03-01T17:08:44

When female bonobos join a new group, they will do anything to get with the "it" crowd — which often means having sex with the alpha female.

And according to new research, females of this promiscuous primate species who are climbing the social ladder will advertise their successes during sex by calling out, especially when their partner is of higher status or when the alpha female is in the audience.

"These females are climbing social ladders," study researcher Zanna Clay, a postdoctoral researcher at Emory University, told LiveScience. "By engaging in these social-sexual interactions, they are showing off their social abilities."

Wild sex
Bonobos, Pan paniscus, are closely related to the chimpanzee. The endangered apes live only in the Democratic Republic of the Congo in central Africa. They are popularly thought of as the lovemaking cousin of the warrior chimp. And, boy, do they like sex. For bonobos, sex serves to ease tensions after conflict, show affection, relay social status, provide excitement and reduce stress. It occurs in virtually all partner combinations and in a variety of positions.

Zanna Clay
Unrelated female bonobos develop social bonds and aggregate together in stable social groups, which lie at the base of their enhanced status in bonobo society. Sex facilitates formation of the bonds and lets females express their social relationships.

Female bonobos leave the group in which they grew up and pick a new family to live among and find mates. The newcomer needs to climb the social ladder, which she does by bonding with high-ranking females in the group. This bonding comes in many forms, from spending time together, grooming and playing with each other, to "having sex" by touching genitals and swaying their hips side to side in unison.

When first entering a new family, the bonobos "don't know anyone, and they don't have kin relations with any of these females," Clay explained. "They have to develop relationships and learn to tolerate one another." Sex relieves their stress.

Calling out
The researchers observed the primates interacting in three enclosures at the Lola Ya Bonobo Sanctuary in the Congo. They also placed bonobos in experimental setups, so they could exclude males from the audience.

They analyzed how several factors influenced the rate of the bonobos' sex calls.

"If they were invited to have sex with a female of high rank, that's the scenario in which they could call out," Clay said. "They were advertising that they had been picked, and they wanted to show that off." The higher-ranked of the pair didn't usually call out.

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The other important factor: the audience. If the alpha female was present, the low-ranking female was more likely to call out during sex. "They are very aware of the alpha female, who is the most relevant group member," Clay said. "When she's around, they are much more likely to advertise these sexual friendships."

What the researchers didn't find was a relationship between physical stimulation and calling out during sex. The length of contact and the position didn't affect the calling rate.

The study was published Thursday in the journal Scientific Reports.

You can follow LiveScience staff writer Jennifer Welsh on Twitter @microbelover. Follow LiveScience for the latest in science news and discoveries on Twitter @livescience and on Facebook.

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