ST. LOUIS — Chimpanzees and gorillas may be different species, but that doesn’t mean they can’t get along, a new study reveals. Scientists from Washington University in St. Louis have found the first evidence that these two primate species not only interact with each other socially, but they also build long-lasting relationships in the wild.
Using more than 20 years of observations at Nouabalé-Ndoki National Park in the Republic of Congo, the team discovered that social ties between individual chimpanzees and gorillas actually lasted for years, and their bonds were the result of a variety of social contexts. These included protection from predators, food-gathering, and information sharing in the wild.
“There are few (if any) studies of interactions between primate species that have been able to take the identity of individuals into account,” says primatologist Crickette Sanz in a university release. “It has long been known that these apes can recognize individual members of their own species and form long-term relationships, but we had not known that this extended to other species.”
“An example of what we found might be one individual traveling through a group of the other species to seek out another particular individual,” the researcher adds. “We were also able to document such interactions over time and in different contexts in this study.”
Interestingly, the majority of the world’s remaining gorillas and chimpanzees live together. Large tracts of forest in the Congo Basin act as a conservation stronghold for these primates, as well as forest elephants, leopards, and many other species.
Gorillas and chimps love to dine at the same places
Looking at primate observations in the Goualougo Triangle from 1999 to 2020, scientists documented all sorts of social interactions between chimps and gorillas — ranging from play to aggressive confrontations. What they learned was that primates live in diverse and socially dynamic environments just like humans do.
“Rather than thinking about chimpanzees alone, we should be thinking about them within diverse and dynamic habitats where they are actively engaging with other species and play an integral role in the persistence of the unique ecosystems in which they exist,” explains co-author David Morgan, a research fellow at Lincoln Park Zoo.
While previous theories have suspected that these relationships are generally based on the need for protection from predators, the new study found little evidence that defense is the main reason gorillas and chimpanzees band together.
“Predation is certainly a threat in this region, as we have cases in which chimpanzees have been killed by leopards,” Sanz says. “However, the number of chimpanzees in daily subgroups remains relatively small, and gorillas within groups venture far from the silverback who is thought to be a protector from predation.”
Instead, the team found that a third (34%) of the interactions between these two species take place while they’re feeding at the same trees. Another 18 percent of these interactions took place while the species were snacking on different foods in close proximity to each other. Simply put, half of the social encounters gorillas and chimps have occur while they’re enjoying meals together.
Best friends forever?
Researchers add that the new observations also reveal social relationships between species which overlap in the same environments can persist for a long time. On several occasions, the team spotted the same gorillas and chimpanzees seeking out a particular partner to engage in play sessions over months and years.
“No longer can we assume that an individual ape’s social landscape is entirely occupied by members of their own species,” says co-author Jake Funkhouser, a doctoral candidate of biological anthropology at Washington University. “The strength and persistence of social relationships that we observed between apes indicates a depth of social awareness and myriad social transmission pathways that had not previously been imagined. Such insights are critical given these interspecies social relationships have the potential to serve as transmission pathways for both beneficial socially learned cultural behaviors and harmful infectious disease.”
Study authors note chimpanzees and gorillas are so closely related, that many viruses are able to jump between the species. One example of this is Ebola, which has devastated ape populations in central Africa.
“While we continue to be concerned about many disease risks, we now know much more about the origin of many of these pathogens and routes of their transmission within and between species, including humans,” Sanz concludes.
In this study, “the surprise to us was the extent of overlap and interaction that occurred between these apes that was previously not recognized or reported. Based on the literature, we had anticipated that the apes would avoid one another… and in some cases, it seemed to be the opposite.”
The findings appear in the journal iScience.