This is not good, since low genetic diversity and high inbreeding may increase the risk of extinction in the present-day species.” “This suggests that recent population declines caused by hunting and habitat destruction have had an impact on the genomes. “However, we also find that present-day rhinos have lower genetic diversity, and higher levels of inbreeding, compared to our historical and prehistoric rhinoceros genomes,” he says. The new approaches and tools they developed can now be applied to studies in other taxonomic groups.ĭalén says that the findings are “partly good news, and partly not.” It appears that low levels of genetic diversity in rhinos is part of their long-term history and hasn’t led to an increase in health problems related to inbreeding and disease-causing mutations. The team had to develop new analysis tools to take those differences into account.
The genome data represented different data types, in part due to the inclusion of both modern and ancient DNA. “When we decided to put together all the rhinoceroses’ data and conduct a comparative genomics study, we also confronted the ‘big data’ problem,” Liu explained. There were some challenges to overcome, says Shanlin Liu, China Agricultural University, Beijing. They realized that if they joined forces, along with colleagues around the world, they could do a comparative study of all living rhinos together with the three species that went extinct during the last Ice Age. Dalén and Tom Gilbert, University of Copenhagen, had been working separately on different rhino species. The new study was inspired at a scientific meeting. Westbury says that rhinos may have purged deleterious mutations in the last 100 years, allowing them to remain relatively healthy, despite low genetic diversity.
This notion is consistent with an apparent lack of accumulated deleterious mutations in rhinos in recent decades. “Continuously low population sizes may indicate that rhinoceroses in general are adapted to low levels of diversity.” “All eight species generally displayed either a continual but slow decrease in population size over the last 2 million years, or continuously small population sizes over extended time periods,” said Mick Westbury of the University of Copenhagen, Denmark. To some extent, this means that the low genetic diversity we see in present-day rhinos, which are all endangered, is partly a consequence of their biology. “The second important finding is that all rhinoceroses, even the extinct ones, have comparatively low genetic diversity. “We can now show that the main branch in the rhinoceroses’ tree of life is among geographic regions, Africa versus Eurasia, and not between the rhinos that have one versus two horns,” says Love Dalén of the Centre for Palaeogenetics and the Swedish Museum of Natural History.
They also find that-while dwindling populations of rhinos today have lower genetic diversity and more inbreeding than they did in the past-rhinoceroses have historically had low levels of genetic diversity. The findings show that the oldest split separated African and Eurasian lineages about 16 million year ago. Now, researchers reporting in the journal Cell on August 24 have helped to fill the gaps in the rhino evolutionary family tree by analyzing genomes of all five living species together with the genomes of three ancient and extinct species. One reason answers have been hard to come by is that most rhinos went extinct before the Pleistocene. There’s been an age-old question going back to Darwin’s time about the relationships among the world’s five living rhinoceros species. In the far background is a woolly rhinoceros ( Coelodonta antiquitatis). In the foreground is a Siberian unicorn ( Elasmotherium sibiricum), and close behind are two Merck’s rhinoceroses ( Stephanorhinus kirchbergensis).
This illustration shows a paleoartist’s reconstruction of the three extinct rhinoceros species whose genomes were sequenced as part of the study.
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