In central Cameroon, two different subspecies of chimpanzees live on opposite banks of the Sanaga River, the only instance of two different chimp subspecies living in the wild in a single country. The area is roughly at the geographic center of the range for all four known subspecies of these great apes.
But when a team of scientists recently took a close look at the genetics of central Cameroon’s wild chimpanzees, they didn’t find two distinct populations; there were three.
“It blew away our assumptions,” said Matthew Mitchell, PhD, a postdoctoral fellow, at Drexel University. “We had always thought that the only genetic difference across populations would be between the two subspecies, and that the differences came from the division across the Sanaga River, but now we see there is more to the picture.” Mitchell was first author of two of three new papers about this chimpanzee research with his advisor Mary Katherine Gonder, PhD, an associate professor in Drexel’s College of Arts and Sciences, other lab members and an international team of collaborators, published this week in BMC Evolutionary Biology.
Mary Katherine Gonder and Paul Sesink Clee (at center of group) processing chimpanzee fecal samples for genetic analyses. Credit George Ghamu
The team’s complementary analyses of population genetics, geographical distribution and habitat use paint a new picture of the evolutionary past and potentially bleak future of the Nigeria-Cameroon Chimpanzee (Pan troglodytes ellioti), already the most endangered chimp subspecies, with about 6,000 individuals estimated in the wild. They are already threatened by illegal hunting and habitat loss to both logging and agricultural plantations.
Now, among other findings, the scientists report that the two distinct populations of the Nigeria-Cameroon chimpanzee have closer ties to their habitats than previously anticipated. And their findings also suggest climate change could cause significant harm to chimpanzee populations due to habitat alterations.
The research team, one of the few groups studying Nigeria-Cameroon chimpanzees in the wild, collected fecal and hair samples for genetic analyses. They also mapped the precise locations of those sample collection sites in addition to locations of reports of chimp sightings and evidence of activity including nests and tools.
“The Nigeria-Cameroon chimpanzee is perhaps the least studied of all chimpanzee subspecies,” said Paul Sesink Clee, a doctoral candidate in Gonder’s lab, who was first author of a paper detailing habitat distribution and modeling impacts of climate change. “This is the first time that their distribution and habitat has been studied in such detail, and the data used to predict how their habitats might degrade under climate change.”
Where Distinct Ecosystems Meet, An Unexpectedly Different Population of Chimps Occurs
Central Cameroon is noteworthy not just as a place where two chimp subspecies meet. It’s also the place where the species-rich, mountainous Gulf of Guinea region abuts the distinct, but comparably diverse, lowland Congo River Basin. Together, these two ecosystems contain about 20 percent of all plant and animal species on the entire planet, and many of those species are endemic—found only here in central Africa.
Habitat Types and Chimpanzee Population History in Cameroon and Nigeria. Credit: Sesink Clee et al.
These different rainforest ecosystems converge with savanna in central Cameroon forming a savanna-woodland mosaic known as an ecotone.
“This ecotone is associated with driving diversification in a lot of different species,” Mitchell said. Ecotones are thought to be important in driving variation and diversification of species all over the world.
This particularly fragile savanna-woodland mosaic habitat in central Cameroon north of the Sanaga River is where Mitchell’s genetic analysis identified a population of Nigeria-Cameroon Chimpanzees that was distinct from those living in the mountainous rainforests of northwest Cameroon and eastern Nigeria. They also determined that the population in the ecotone div