December 13, 2009 | 8
What genetic machinations are behind the much adored, bamboo-chomping giant panda (Ailuropoda melanoleuca)?
An international team of more than 120 researchers has now sequenced this rare bear’s genome. It is the first genome project to rely solely on short-read next-generation sequencing technology, and the panda’s sequence is the first in the bear family and only the second member of the Carnivora order (after dogs) to be decoded, report the researchers. The findings were published online Sunday in Nature (Scientific American is part of Nature Publishing Group).
Giant pandas have long been a biological curiosity, owing in part to their strict bamboo diet and low rate of reproduction. But as human development has sprawled, the endangered pandas‘ numbers have dwindled—down to an estimated 2,500 to 3,000 wild individuals, so learning more about what makes these animals tick may prove important in conservation efforts.
Indeed, the new genetic insights—gleaned in this study from the genes of a three-year-old female from the Chengdu breeding center in China—have answered some old questions. By parsing genes involved in the digestive process, the researchers found that, "the panda probably has all the necessary components for a carnivorous digestive system," the paper authors wrote, a finding that makes sense given its place in Carnivora and the Ursidae family. So, "the bamboo diet of the panda is unlikely to be dictated by its own genetic composition, and may instead be more dependent on its gut microbiome" for digestion, they concluded.
What, then, might draw a would-be meat-eater to faithfully devour such fibrous feasts? It might be a matter of taste, the researchers found. The lesser-known flavor profile umami, which is tasted in a common amino acid (glutamic acid), is aided by the presence of a number of T1R genes. In the panda’s genetic map, the T1R1 gene appeared to not function, which "might prevent the panda from expressing a functional umami taste receptor," wrote the authors. Thus, the big bear might not share other carnivores’ affinity for meaty, high-protein meals.
Despite the research success in the digestion department, however, the new genetic profile, which covered about 94 percent of the panda’s genome, hasn’t yet explained the species’ low fecundity rate.
Comparing the panda genome to those of the dog and human, the researchers were also able to gain a glimpse into evolutionary processes. They found, for instance, that the panda, which likely split from the main Ursidae line early, has a lower divergence rate than the dog. Additional insight into more mammals should also assist in better understanding the human genome.
Image courtesy of Zhihe Zhang