How the Panda’s “Thumb” Evolved Twice


From Scientific American:

The two species share a common ancestor that lived more than 40 million years ago. Giant pandas (Ailuropoda melanoleuca) are distant relatives of other bears, whereas red pandas (Ailurus fulgens) are more closely related to ferrets. Both species subsist on a diet composed almost entirely of bamboo, with the help of a false digit.

The pandas’ ‘thumbs’—which are actually abnormally enlarged wrist bones—allow both species to grip and handle bamboo with remarkable dexterity. But “exactly how such evolutionarily distant animals evolved such a similar lifestyle and body form has long been a mystery,” says Steve Phelps, a geneticist at the University of Texas at Austin.

In a new study, Wei Fuwen and Hu Yibo, conservation geneticists at the Chinese Academy of Sciences’ Institute of Zoology in Beijing, and their colleagues, produced the first genome sequence of the red panda and compared it with the giant panda genome. This comparison turned up a list of 70 genes that showed signs of evolutionary change in both species.

Two of the genes, DYNC2H1 and PCNT, are important for limb development, and mutations in these genes can cause bone and muscle abnormalities, including extra digits, in mice and humans. Both pandas also share single amino-acid changes in the proteins encoded byDYNC2H1 and PCNT that are not found in 60 other mammal species. The researchers propose that these changes could have contributed to the pandas’ false thumbs.

Seven other genes on the list—including those involved in absorbing vitamins and amino acids that the body cannot produce—may have helped both pandas subsist on nutrient-poor bamboo, says Wei. The team’s findings were published on January 16 in Proceedings of the National Academy of Sciences USA.

Andrew Foote, an evolutionary biologist at Bangor University, UK, says that the team has come up with a “very strong” list of candidates to explain the pandas’ shared adaptations to a unique lifestyle. …

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