This week's paper is from PNAS, lead authored by Yibo Hu at the Chinese Academy of Sciences in Beijing. The authors studied the genetics behind the extraordinary similarities of giant pandas (Ailuropoda melanoleuca) and red pandas (Ailurus fulgens) which have overlapping distributions in the Sichuan province of China. Both giant and red pandas are herbivores that consume almost exclusively bamboo. They also both have appendages on their forepaws called "pseudothumbs" that are projections from bones in the wrist (technically called an enlarged radial sesamoid), allowing them to grasp stalks of bamboo. What is particularly surprising is that these two "pandas" are not each other's closest relatives. Rather, the giant panda is most closely related to other bears, and red pandas are most closely related to skunks, raccoons, and weasels. This means that giant and red pandas separately evolved from a meat-eating ancestor (after all they are both in the order Carnivora). The evolution from meat-eating to bamboo-eating requires a large range of physiological changes. When two organisms that are not closely related independently evolve similar traits it is called convergent evolution. To study the convergent evolution of pandas, Hu and colleagues sequenced the entire genomes of both panda species.
The authors estimate that giant and red pandas shared a common ancestor some 47. 5 million years ago. To put that in perspective, humans and chimpanzees last shared a common ancestor around 10 million years ago. The authors found 70 genes that convergently evolved in the two pandas. For the majority of these genes the function is still unknown, but two of them are involved in the development of the pseudothumb, and three genes are involved in the digestion of dietary protein. They also found four convergent genes that function in the utilization of vitamins. Not only have the pandas acquired genes in common, they have also lost a total of 10 genes in common. The gene for the umami taste receptor (often described as savory taste receptor, but involved in the detection of meat flavors) is non-functional in both pandas.
Few studies have used entire genomes to study convergent evolution. But as high-throughput DNA sequencing advances in speed and affordability it is likely to become more and more common.