- Two wild bonobos in the Luo Scientific Reserve in the Democratic Republic of the Congo were observed to adopt infants from different social groups, according to a new study.
- These are said to be the first recorded cases of great apes adopting unrelated individuals.
- While the researchers do not know why these bonobos chose to adopt unrelated infants, they speculate that it could be to strengthen current and future alliances within their own groups as well as with other social groups.
Nahoko Tokuyama says she couldn’t believe what she was seeing when she noticed the wild bonobo with an unknown infant on her back in the Luo Scientific Reserve in the Democratic Republic of the Congo. The bonobo, an 18-year-old named Marie, already had two young offspring — 2-year-old Margaux and 5-year-old Marina. Marie hadn’t recently given birth, so it seemed strange that she suddenly had a baby, Tokuyama said.
“I didn’t believe my eyes because I didn’t expect it,” Tokuyama, assistant professor at the Center for International Collaboration and Advanced Studies in Primatology (CICASP) and the Primate Research Institute at Kyoto University, told Mongabay in an interview. “I knew the number of infants in the group, and suddenly, there was one more infant. I counted again and again [and] finally I took a picture of the infant. Then I finally could believe it. It was very surprising.”
Tokuyama and her colleagues studied Marie and her group members to try and figure out what was going on. In April 2019, they noticed Marie carrying, grooming, nursing, and sharing food with the infant, who they eventually identified as Flora, the offspring of Fula, a bonobo from another social group. While no one knows what happened to Fula, the researchers came to understand that Marie had adopted Flora as her own, despite being unrelated to her and from a different social group.
This wasn’t an isolated incident. In October 2019, the researchers observed a similar thing happening in another bonobo social group. This time, a post-menopausal female named Chio had adopted a 3-year-old named Ruby, who was from yet another social group.
“For many years, we couldn’t observe bonobos because of the civil war in the Congo, so bonobos are understudied apes,” said Tokuyama, who was the lead author of a new paper on the subject. “We are not sure if cross group adoption happens all the time, or if this is the first case. And we are also not sure why we observed two cases within a short time period.”
Bonobos (Pan paniscus), one of the four great apes, are said to share approximately 98.7% of their DNA with humans, about the same amount that chimpanzees share with us. But while adoption is common between humans, researchers have never observed a great ape adopting an unrelated infant before. Chimps have been known to adopt orphans related to them on the maternal side, but they are usually aggressive toward chimps from different social groups, Tokuyama said.
“If chimpanzees see infants of another group, they can kill them,” Tokuyama said. “But in bonobos, in our case, they accepted the infant from another group, and we didn’t see any aggressive attitude to that infant. That is quite amazing in the animal world.”
While the reasons for Marie and Chio adopting unrelated infants remains a mystery, the researchers speculate that it could be due to a desire to strengthen current and future alliances within their own bonobo groups as well as other groups.
Tokuyama and her team had to cut short their study in the Luo Scientific Reserve due to the COVID-19 pandemic, but they have been able to get reports from local assistants. As of October 2020, Marie was still caring for Flora, and Chio for Ruby.
“Adoption in wild bonobos goes beyond the boundaries of social groups and is not necessarily related to kin relationships or to pre-existing social relationships between adoptive and biological mothers,” Tokuyama and her colleagues wrote in the paper. “The current cases of cross-group adoption may have been enabled or driven by bonobos’ altruism, strong attraction to infants, and/or high social tolerance towards out-group individuals. Recognizing this may contribute to a better understanding of adoption in humans.”
Bonobos are classified as an endangered species by the IUCN, with an estimated 15,000 to 20,000 individuals left in the wild as of 2016. The main threats to the species are poaching, habitat loss, and the spread of disease, mainly via transmission from humans.
John Hart, a bonobo expert and the scientific director of the Lukuru Wildlife Research Foundation in the Democratic Republic of the Congo, said he was very interested to read the paper.
“This is a fascinating report, and though there are tantalizing details missing (such [as] what happened to the biological mothers in both cases, and how did these transfers happen), the DNA evidence that the young animals and their adopted mothers are not biologically related is convincing that the cases are real,” Hart told Mongabay in an email.
“Bonobos are difficult to watch in the wild, more so than chimpanzees perhaps, and much behavior can be subtle, nuanced even,” he added. “These discoveries show the value of long term study groups, with well-known individuals monitored over the years.”
Tokuyama also noted the importance of long-term studies for a species like bonobos, which she said helped enable this discovery.
“We have studied [these groups] for almost 50 years, and these are the first episodes [we observed],” she said. “We want to continue this long-term research to observe these kinds of thought-provoking cases.”
Correction (24/3/2021): A previous version of this story inaccurately stated that Marie was carrying, grooming, nursing, and sharing food with Flora between September 2017 and March 2019. This was changed to say that these events were observed in April 2019.
Hobaiter, C., Schel, A. M., Langergraber, K., & Zuberbühler, K. (2014). ‘Adoption’ by maternal siblings in wild chimpanzees. PLOS ONE, 9(8), e103777. doi:10.1371/journal.pone.0103777
Tokuyama, N., Toda, K., Poiret, M., Iyokango, B., Bakaa, B., & Ishizuka, S. (2021). Two wild female bonobos adopted infants from a different social group at Wamba. Scientific Reports, 11(1). doi:10.1038/s41598-021-83667-2
Banner image caption: Marie grooming Flora. Image by Nahoko Tokuyama.
Elizabeth Claire Alberts is a staff writer for Mongabay. Follow her on Twitter @ECAlberts.
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