Evidence for Ancient Admixture in Bonobos

The ancestry and evolution of non-human primates such as chimps and bonobos is not as well-represented in the fossil record as that of humans. Genetic research and identification of evidence for admixture in chimp and bonobo populations may help to resolve some of this uncertainty.

In their paper, Kuhlwilm et al. (2018) analyze whole-genome data on 69 bonobos and western and central chimpanzees to identify ancient introgression into the bonobo genome. Using S* statistics, a measure of linkage and linkage disequilibrium, the researchers were able to identify areas in the central chimpanzee genomes that were more alike bonobos than expected by chance. This result suggested at least unidirectional historical gene flow from bonobos to central African chimpanzees after the initial split around 2 Ma. Gene flow from chimps into bonobo populations is also highly likely, but more difficult to discern from the results.

Kuhlwilm et al. also discovered evidence for introgression from a mystery archaic population that likely diverged from the chimp and bonobo common ancestor around 3- 3.5Ma. Between ~2.6-3.7% of the genomes of each sampled individual show evidence for introgressed sequences. These are inferred to have likely come from admixture events about 300-600 Ka, though these values have a wide confidence interval. Finally, the researchers suggest that certain regions of persistent introgressed sequences, such as immune related genes SERPINA 11 and SERPINA 9, were retained due to the evolutionary advantages they conferred.

Audrey Tjahjadi

Link to original article: https://www.nature.com/articles/s41559-019-0881-7.pdf