2 march 2012

Chimps show much greater genetic diversity than humans

Science

Chimpanzee
The researchers found chimpanzees from different populations were substantially more different genetically than humans living on different continents.

Groups of chimpanzees within central Africa are more different genetically than humans living on different continents, an Oxford University-led study has found.

The study published in the journal PLoS Genetics suggests that genomics can provide a valuable new tool for use in chimpanzee conservation. It has the potential to identify the population of origin of an individual chimpanzee or the provenance of a sample of bush meat.

Common chimpanzees in equatorial Africa have long been recognized as falling into three distinct populations or sub-species: western, central and eastern chimpanzees. A fourth group, the Cameroonian chimpanzee, has been proposed to live in southern Nigeria and western Cameroon, but there has been considerable controversy as to whether it constitutes a distinct group.

Oxford University researchers, along with scientists from the University of Cambridge, the Broad Institute, the Centre Pasteur du Cameroun and the Biomedical Primate Research Centre, examined DNA from 54 chimpanzees. They compared the DNA at 818 positions across the genome that varied between individuals.

Their analysis showed that Cameroonian chimpanzees are distinct from the other, well-established groups. And previous conclusions that Cameroonian and western chimpanzees are most closely related were shown to be untrue. Instead, the closest relationships to Cameroonian chimpanzees are with nearby central chimpanzees.

Dr Rory Bowden from the Department of Statistics at Oxford University, who led the study, said: 'These findings have important consequences for conservation. All great ape populations face unparalleled challenges from habitat loss, hunting and emerging infections, and conservation strategies need to be based on sound understanding of the underlying population structure. The fact that all four recognized populations of chimpanzees are genetically distinct emphasizes the value of conserving them independently.'

The fact that all four recognized populations of chimpanzees are genetically distinct emphasizes the value of conserving them independently.

Dr Rory Bowden

The researchers also contrasted the levels of genetic variation between the chimpanzee groups with that seen in humans from different populations.

Surprisingly, even though all the chimpanzees live in relatively close proximity, chimpanzees from different populations were substantially more different genetically than humans living on different continents. That is despite the fact that the habitats of two of the groups are separated only by a river.

Professor Peter Donnelly, director of the Wellcome Trust Centre for Human Genetics at Oxford University and a senior author on the study, noted: 'Relatively small numbers of humans left Africa 50,000-100,000 years ago. All non-African populations descended from them, and are reasonably similar genetically.'

'That chimpanzees from habitats in the same country, separated only by a river, are more distinct than humans from different continents is really interesting. It speaks to the great genetic similarities between human populations, and to much more stability and less interbreeding over hundreds of thousands of years in the chimpanzee groups.'

The conservation implications of the study extend to other species. New techniques such as next-generation sequencing will allow a catalogue of genetic variation to be obtained cheaply and easily for any species. Such a catalogue could then be used to identify genetically distinct groups in studies like this one.

Dr Nick Mundy from the University of Cambridge said: 'Because they are humans’ nearest relatives, the structure and origins of chimpanzee populations have long been of wide interest. Future studies will be able to use genome data to uncover the adaptations that are unique to the Cameroonian chimpanzees.'