Environmentalists have long known that Sumatran rhinos are on the brink of extinction. But their population may have been declining for many more years than previously thought.
An international team of researchers sequenced the whole genome of the rare rhino species for the first time. The sample came from Ipuh, a well-known male rhino who lived at the Cincinnati Zoo for more than two decades before he died in 2013.
"Our genome sequence data revealed that the Pleistocene was a roller-coaster ride for Sumatran rhinoceros populations," study author Herman Mays Jr., who teaches genetics at Marshall University, said in a statement.
The Pleistocene period spanned from 2.6 million to 11,700 years ago. Mays and his colleagues found that the rhino population peaked during this era. But toward the end of this time period, the rhinos, along with other large mammals, began to suffer. Based on the new genome evidence, there were only about 700 Sumatran rhinos left 9,000 years ago.
"The population bottomed out and never showed signs of recovery," Mays said.
As of 2017, there are fewer than 100 Sumatran rhinos left in the world, according to the World Wide Fund For Nature.
To conduct their research, the team used a method known as pairwise sequentially Markovian coalescent (PSMC), which involves the genome sequence of a single individual—Ipuh, in this case—to estimate thousands of generations worth of demographic history. Additionally, the team combined the PSMC data with climate data to understand the connection between the two.
Their study, published in the journal Current Biology, concluded that climate change had a great impact on the available habitat.
Changes in the region of Southeast Asia known as Sundaland, which included that habitat, likely isolated Sumatran rhinoceros populations. "By the end of the Pleistocene, the Sundaland corridor was submerged, and populations were fragmented," the authors write. That fragmentation led to their decline.
But humans are to blame, too. As they settled on the land, deforestation drove the rhinos out of the area. People also hunted the vulnerable animals, contributing to their quick decline.
As of 2015, wild Sumatran rhinos officially went extinct in Malaysia. Only two remain in the country—Tam and Iman—but both are in captivity, according to the Borneo Rhino Alliance.
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