New genetic analysis of wild baboons in southern Kenya shows that most carry traces of hybridization in their DNA. Due to hybridization, about one-third of their genetic makeup consists of genes from another closely related species.
The study was conducted in an area near Amboseli National Park in Kenya, where yellow baboons occasionally meet and mix with their Anubis baboon neighbors living in the northwest.
Since 1971, researchers have monitored the animals almost daily, noting when they mate with outsiders, and how the resulting offspring perform over their lifetimes as part of the Amboseli Baboon Research Project, which is One of the longest-running field studies on wild primates. world.
Yellow baboons have tawny fur with white cheeks and undersides. Anubis baboons have green-grey fur, and the males have shaggy manes on their heads. Although they are distinct species that diverged 1.4 million years ago, they can interbreed where their ranges overlap.
In any case, the descendants of these unions are well managed. Fifty years of observation haven’t found any clear sign that hybrids perform worse than their peers. Some were even better than expected: Baboons with more Anubis DNA in their genomes matured faster and formed stronger social bonds, while males were more successful at winning mates.
But new genetic findings, published Aug. 5 in the journal Science, suggest that looks can be deceiving.
Jenny Tung, a Duke professor who led the project with doctoral students Tauras Vilgalys and Arielle Fogel, said the study sheds light on how the diversity of species on Earth is maintained even when genetic lineages between species are blurred.
Interspecies mating is very common in animals, said Fogel, a doctoral candidate in Duke’s genetics and genomics program. About 20 to 30 percent of apes, monkeys and other primate species interbreed and mix their genes with other species.
Even modern humans carry mixed genes from now-extinct relatives. As much as 2% to 5% of the DNA in our genome points to past interbreeding with Neanderthals and Denisovans, ancient humans that our ancestors encountered and mated with while migrating from Africa to Europe and Asia . These contacts left a genetic legacy that still lingers today, influencing our risk of depression, blood clots, and even tobacco addiction or complications from COVID-19.
The researchers wanted to understand the possible costs and benefits of this genetic mixing in primates, including humans. But modern humans stopped interbreeding with other ancient humans tens of thousands of years ago, when all but one species—ours—extinct. However, Amboseli’s wild baboons make possible primate hybridization, which is still being studied.
The researchers analyzed the genomes of about 440 Amboseli baboons spanning nine generations, looking for fragments of DNA that may have been inherited from Anubis immigrants.
They found that all baboons in the Amboseli Basin in southern Kenya today are hybrids, with Anubis DNA making up an average of 37 percent of their genomes. Due to recent interbreeding, some have Anubis ancestry, for the past seven generations. But for nearly half of them, the mixing occurred much earlier, hundreds to thousands of generations ago.
During that time, data showed that certain segments of Anubis DNA affected their survival and reproduction at the expense of the hybrids that inherited them, so much so that the genes were unlikely to be present in the genomes of today’s descendants. , said Vilgalys, now a postdoctoral scholar at the University of Chicago.
Their results are consistent with human genetic studies, which suggest that our early ancestors also paid a price for hybridization. But what exactly Neanderthal and Denisovan genes did to cause their harm is difficult to tease out from the limited fossil and DNA evidence available.
Amboseli’s baboons provide clues to the cost of hybridization, the researchers said. Using RNA sequencing to measure gene activity in baboon blood cells, the researchers found that natural selection was more likely to clear borrowed DNA segments that act as switches, turning other genes on and off.
The next step, Fogel said, is to pinpoint more precisely what ultimately affects the ability of these hybrid baboons to survive and reproduce.
Genomic data allows researchers to look back over many more generations and study historical processes not directly visible in the field, Vilgalys said.
“But you need to look at the animals themselves to understand what the genetic changes really mean,” Dong said. “You need fieldwork and genetics to understand the whole story.”
“We’re not saying that’s what Neanderthal and Denisovan genes did in humans,” added Tung, now at the Max Planck Institute for Evolutionary Anthropology in Germany. “But the baboon case clearly shows that the genomic evidence for the cost of hybridization can be consistent with animals that not only survive but often thrive.”
This research was supported by grants from the National Science Foundation (NSF IOS 1456832, BCS-1751783, BCS-2018897, DGE #1644868), the National Institutes of Health (R01AG053308, R01AG053330, P01AG031719, R01HD088558, T32GM007754), the Leakey Foundation and North Carolina Center for Biotechnology (2016-IDG-1013).