There are currently five species of rhinoceros living on the Earth - Indian, Javan, Sumatran, white and black. But piecing together exactly how they are related has proven problematic thanks to a lack of genetic data.
Now, a study by an international team of researchers has helped to fill the gaps in the rhino evolutionary family tree by analysing and comparing the genomes of all five living species along with the genomes of three extinct species - woolly, Merck’s, and the Siberian Unicorn.
“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,” said study author Prof Love Dalen of the Centre for Palaeogenetics and the Swedish Museum of Natural History.
“The second important finding is that all rhinoceroses, even the extinct ones, have comparatively low genetic diversity. 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.”
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They found that all eight species showed a slow decrease in population size over the past two million years or had consistently small populations over extended periods of time – this may mean that rhinoceroses are naturally adapted to living in groups with low genetic diversity, the researchers say.
This theory fits with the currently held idea that rhino populations have not accumulated disease-causing genetic mutations over the past 100 years, allowing them to stay healthy despite inbreeding and low genetic diversity.
The findings also mean that conservation programs designed to help rhino numbers recover should perhaps switch from focussing on increasing genetic diversity to increasing population sizes, the researchers say.
However, rhino numbers are dwindling. According to charity Save the Rhino, there are around 5,000 black and 18,000 white rhinos remaining in Africa, 3,500 Indian rhinos, and fewer than 100 Javan and Sumatran rhinos in southeast Asian.
Reader Q&A: How does trophy hunting affect wild animal populations?
Asked by: Steven White, Bromley
Since the days of the Roman Empire, wild animals have been slaughtered to prove power and wealth. Bigger is better when it comes to this ‘sport’, which means that dominant, mature male rhinos, elephants, lions, leopards and other animals are the prime targets of hunters.
The artificially premature loss of strong, healthy individuals takes vital genes out of the breeding pool which, over time, can result in an overall decline in body size and, where applicable, also horn or tusk size.
Removing these frontline animals also undermines social cohesion and can leave members of prides and herds vulnerable to attack by other members of their own species. Although some argue that money from trophy hunting can help with conservation, there is not enough evidence to convince us that it can.
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