Study: Bonobo Mothers Play Strong Role in Helping Adult Sons Find Mate

In many group-living mammals, mothers may increase the reproductive success of their adult daughters. However, whether such maternal effects exist for adult sons is largely unknown. A new study, published in the journal Current Biology, shows that adult bonobo males have higher paternity success when their mother is living in the group: from physically preventing other males from mating to bringing their sons in close proximity to fertile females, bonobo mothers increase their sons’ chance of fatherhood three-fold.

A young juvenile male bonobo is groomed by his mom in the Kokolopori Bonobo Reserve, the Democratic Republic of Congo. Image credit: Martin Surbeck.

A young juvenile male bonobo is groomed by his mom in the Kokolopori Bonobo Reserve, the Democratic Republic of Congo. Image credit: Martin Surbeck.

“This is the first time that we can show the impact of the mother’s presence on a very important male fitness trait, which is their fertility. We were surprised to see that the mothers have such a strong, direct influence on the number of grandchildren they get,” said study first author Dr. Martin Surbeck, a primatologist at the Max Planck Institute for Evolutionary Anthropology, Germany.

Dr. Surbeck and colleagues observed wild populations of bonobos (Pan paniscus) in the Democratic Republic of Congo, as well as wild populations of chimpanzees in Côte d’Ivoire, Tanzania, and Uganda.

The researchers found that while both bonobo and chimpanzee mothers would advocate for their sons in male-on-male conflicts, bonobo moms went the extra mile to aid their sons’ copulation efforts.

This involved protecting their sons’ mating attempts from other males, intervening in other male’s mating attempts, and intentionally bringing their sons around fertile females.

The bonobo mothers were also able to use their rank in the bonobo’s matriarchal society to give their sons access to popular spots within social groups in the community and help them achieve higher status — and therefore, better mating opportunities.

“These interactions were rare in chimpanzee societies likely because males hold dominant positions over females, making the actions of chimp mothers less influential than those of bonobo mothers,” the scientists said.

“Interestingly, bonobo moms did not extend similar help to their daughters, nor were there any observations of daughters receiving assistance in rearing their offspring.”

“In bonobo social systems, the daughters disperse from the native community and the sons stay. And for the few daughters that stay in the community, which we don’t have many examples of, we don’t see them receiving any help from their mothers,” Dr. Surbeck said.

Moving forward, the authors would like to better understand the benefits these behaviors confer on bonobo mothers. Currently, they think that it allows for an indirect continuation of their genes.

“These females have found a way to increase their reproductive success without having more offspring themselves,” Dr. Surbeck said.

“The prolongation of the post-reproductive human female lifespan, as well as the early age at which human women can no longer bear children, may have evolved from this indirect method of continuing their genetic line.”

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Martin Surbeck et al. 2019. Males with a mother living in their group have higher paternity success in bonobos but not chimpanzees. Current Biology 29 (10): R354-R355; doi: 10.1016/j.cub.2019.03.040

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