Chimpanzees and bonobos

Chimpanzees and bonobos interbred during the past half million years, a new study has found – and it is a discovery that could have major implications for policing the illegal trade in apes.

The study provides the first evidence that the confirmed interbreeding between Neanderthals and other hominids was not unique among the higher primates.

A research team led by Marc de Manuel, a biologist at the Institute of Evolutionary Biology of Barcelona in Spain, analysed the genomes of 10 bonobos and 65 wild-born chimpanzees from across Africa.

The team’s findings, published this week in Science, suggest that evolution in the ape world may have involved quite a bit of cross-species hanky-panky.

“This is the first study to reveal that ancient gene flow events happened amongst the living species closest to humans – the bonobos and chimpanzees,” says Tomàs Marquès-Bonet, also at the Institute.

“It implies that successful breeding between close species might have been actually widespread in the ancestors of humans and living apes.”

The study spanned all four subspecies of chimpanzee – the eastern, central, western and Nigeria-Cameroon chimps – and the entire range of habitat, involving animals from 10 countries across tropical Africa.

According to the findings, genetic intermingling has occurred at least twice since the two species diverged from a common ancestor some two million years ago.

Around 1% of the genomes of central, eastern and Nigeria-Cameroon chimps was found to be derived from bonobos.

“We found that central and eastern chimpanzees share significantly more genetic material with bonobos than [do] the other chimpanzee subspecies,” explains Yali Xue, from the Wellcome Trust Sanger Institute in the UK.

“This shows that there wasn’t a clean separation, but that the initial divergence was followed by occasional episodes of mixing between the species.”

The researchers estimate that central chimps – the most genetically diverse subspecies – probably shared genes with bonobos between 550,000 and 200,000 years ago.

Among some subspecies, the bonobo genes had since been deleted, suggesting hybridisation wasn’t always beneficial.

Crucially, the team confirmed it was possible to figure out a chimp’s country of origin from its genetic information.

Because chimp and bonobo populations suffer from illegal capturing, this finding could be significant for conservation efforts.

“This is the largest analysis of chimpanzee genomes to date and shows that genetics can be used to locate quite precisely where in the wild a chimpanzee comes from,” explains co-author Chris Tyler-Smith, also from the Wellcome Trust Sanger Institute.

“This can aid the release of illegally captured chimpanzees back into the right place in the wild, and provide key evidence for action against the captors.”