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5 Oct 07
Cambodia's National Animal Is "Real," Study Says
Anne Casselman for National Geographic News
A recent genetic analysis of a Cambodian ox called a kouprey matches fossil evidence that proves Cambodia's national animal is indeed its own species.
The latest study joins a growing body of evidence showing that the kouprey (pronounced "ko-prah") is not a hybrid between two related species of ox, the banteng and zebu, as was previously suggested.
French evolutionary biologists Alexandre Hassanin and Anne Ropiquet at the National Museum of Natural History in Paris, France, sequenced kouprey DNA and compared it to that of related wild and domestic oxen species.
There are two types of DNA in a cell: nuclear DNA and mitochondrial DNA (mtDNA). Nuclear DNA is a combination of maternally and paternally inherited genes, and mtDNA is inherited exclusively from the mother. Hassanin analyzed both types of DNA in the new study.
"These molecular data allow us to study the evolutionary history of both paternal and mitochondrial lineages," he wrote by email from Vietnam.
If the kouprey is a hybrid of its close oxen relatives, its nuclear genes would have been a combination of the two hypothetical parent species. Instead Hassanin found that the kouprey's nuclear sequences differed from those of banteng and zebu.
"Our interpretations are therefore that the kouprey is a real wild species, different from all other wild oxen," wrote Hassanin.
The study will appear in the November issue of the journal Proceedings of the Royal Society B.
Disappearing National Icon
The kouprey, which resembles a dark-coated ox with massive, curling horns, was first recognized as a species in 1937. In 1960 Cambodia made it the national symbol.
But habitat destruction and hunting took its toll, and many experts believe the last scientific observation of the animal in the wild was in 1957.
"I cannot imagine that if there were any kouprey left today we wouldn't be aware of them," said Gary J. Galbreath, an evolutionary biologist at Northwestern University in Evanston, Illinois, who was not involved in the study.
"But I would love to be proven wrong."
In 1961 German zoologist Herwart Bohlken suggested that the kouprey might be a hybrid population of the banteng and zebu because of similarities between the animals' skulls.
Galbreath and his colleagues tested that hypothesis in a 2006 Journal of Zoology study by comparing kouprey and banteng mtDNA. If the hybridization hypothesis was correct, the mtDNA of both animals would be similar.
"We ran the DNA, and lo and behold, our prediction was correct," Galbreath said. "We now know that this [new study] is Murphy's law in action, but at the time it seemed very convincing."
But that December a fossil kouprey skull, described by Thai scientists Chavalit Vithayanon and Naris Bhumpakphan in 2004, came to Galbreath's attention. The skull possibly dated back to the late Pleistocene or early Holocene epoch, about 125,000 to 5,000 years ago.
"You can't have a fossil kouprey skull if the kouprey is a recent hybrid," he said.
Galbreath and his colleagues formally rescinded their previous view that the kouprey was a hybrid in the March 2007 Journal of Zoology.
Given that the kouprey was its own species after all, the question remained, how did it come to share mtDNA with the banteng?
The genetic data published by Hassanin and Ropiqet suggest that at some point in the Pleistocene, a female kouprey and a male ancestor of today's banteng mated, and that this coupling occurred at least once.
Somehow their offspring spread its maternally inherited kouprey mitochondrial DNA throughout the banteng population.
The artifact of this ancient hybridization event is that banteng carry kouprey mtDNA.
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