It looks like a carnivore, has a digestive tract like a carnivore - but its staple diet is bamboo. Any other member of the ursidae would starve on this cellulose-rich fare. How does the Giant Panda get enough energy to keep itself alive? In January 2010, a study of the panda's genome revealed that it has maintained the genetic requirements for being purely carnivorous, despite being a herbivore. Further, no evidence of genes that encode enzymes for digesting cellulose was found. The hypothesis proposed at that time was that the bamboo diet "may instead be more dependent on its gut microbiome". Now this hypothesis has been tested and validated. This is from a report in Nature News:
"Fuwen Wei, an ecologist at the Institute of Zoology at the Chinese Academy of Sciences in Beijing, and his colleagues took a closer look at the microbes that live in the guts of giant pandas. The team collected stool samples from seven wild pandas in the Qinling and Xiangling mountains in central and western China, as well as from eight captive pandas. By sequencing stool DNA, the researchers determined the different kinds of bacteria present, as well as the identity of thousands of microbial genes. Although wild and captive pandas have different diets and lifestyles - the captive pandas eat a more diverse diet that includes fruit and milk - they tended to harbour similar microbe species in their guts. Wei's team found that samples from both groups contained previously unknown genes produced by Clostridium bacteria, which resembled known genes for enzymes that break cellulose into simpler sugars. The microbial enzymes may help giant pandas to extract extra energy from the small amount of bamboo that they manage to process, says Wei."
How can an animal that has the characteristics of a carnivore eat bamboo? (Source here)
Interestingly enough, most of the gut flora was similar to other carnivores. This is from the Nature News report:
"Most herbivores have developed ways to break down cellulose into sugars; for example, cows and other ruminants have complicated digestive systems - involving multiple stomachs filled with microbes - that process plants many times to extract the maximum nutrition. But pandas are bears, a generally carnivorous family, and neither produce the enzymes necessary to digest cellulose nor harbour the same microbes as ruminants. A broad survey of animal gut microbes found that pandas' microorganisms resembled those of black bears, polar bears and other meat-eaters."
So, although the Panda gut appears to be appropriate for a carnivore, it does not eat meat. As the genome paper (2010) revealed, "The giant panda has lost the capability of sensing umami, which means that meat has become unappetizing." Now, a Chinese team has found evidence for cellulose matabolising microbes that are unique to mammals. This is from their research paper:
"Our metagenomic analysis and 16S rRNA gene data confirm the presence of putative cellulose-metabolizing symbionts in this little-studied microbial environment and clarifies how giant pandas are able to partially digest bamboo fibers despite a genome lacking enzymes that can degrade cellulose."
The mystery is revealed! But what should we make of it all? The Chinese researchers explain it in terms of evolutionary adaptation:
"It is becoming increasingly clear that giant pandas possess a suite of evolutionary adaptations for the highly specialized herbivory. Our findings offer a more in-depth look at the microbiome of a species that occupies an interesting place in the evolutionary tree and has an unusually narrow diet. Thus, the putative harboring of cellulose and hemicellulose-digesting microbes in the gut of the giant panda, along with a suite of other traits, including pseudo-thumbs; well-developed teeth, mandible and skull morphology, and chewing muscles; high-volume food ingestion (12.5 kg/day); brief digestion time; and high mucous levels in the digestive tract, likely have arisen as a result of adapting to a highly fibrous bamboo diet within the constraints imposed by the panda's innate carnivore-like digestive system."
It is this conclusion that prompts some cautionary words in this blog. Adaptions they likely are, but the context for these adaptations is degeneration rather than any increase in biological information. These adaptations fit the pattern of "evolutionary tinkering" so beloved by evolutionists. They do not reveal the "exquisite design" that is so often found when we look in detail at living things. Darwinian mechanisms have not equipped the Panda with the genetic information to digest cellulose. They have not led to changes in the gut to make the process of digesting cellulose more efficient. One report put it this way:
"Wei and his team believe that some of the bacteria they've found in the panda stools help the bears break down that cellulose, if only a little bit. A very little bit. In a study conducted at the Washington National zoo several years ago, it was found that pandas only process something like eight percent of the cellulose in the bamboo they eat. Thus, they have to eat not just a lot, but constantly to get enough nutrition from the bamboo to survive."
So the Giant Panda is not an example of a species that is more fit because of adaptation. Rather, it looks more like a species that has suffered some major degenerative mutations in the past, but has (by a process of "tinkering" with what's still working) managed to survive. The design perspective gives us a story of how a superbly designed carnivore has managed to survive the effects of genetic degradation. Design perspectives are needed, also, if we are to secure a future for the Giant Panda - if we leave it to experience the effects imposed by blind Darwinian mechanisms, it will not be long before the species becomes extinct.
Evidence of cellulose metabolism by the giant panda gut microbiome
Lifeng Zhu, Qi Wu, Jiayin Dai, Shanning Zhang, and Fuwen Wei
Proceedings of the National Academy of Sciences, Published online before print October 17, 2011, doi: 10.1073/pnas.1017956108
Abstract: The giant panda genome codes for all necessary enzymes associated with a carnivorous digestive system but lacks genes for enzymes needed to digest cellulose, the principal component of their bamboo diet. It has been posited that this iconic species must therefore possess microbial symbionts capable of metabolizing cellulose, but these symbionts have remained undetected. Here we examined 5,522 prokaryotic ribosomal RNA gene sequences in wild and captive giant panda fecal samples. We found lower species richness of the panda microbiome than of mammalian microbiomes for herbivores and nonherbivorous carnivores. We detected 13 operational taxonomic units closely related to Clostridium groups I and XIVa, both of which contain taxa known to digest cellulose. Seven of these 13 operational taxonomic units were unique to pandas compared with other mammals. Metagenomic analysis using ~37-Mbp contig sequences from gut microbes recovered putative genes coding two cellulose-digesting enzymes and one hemicellulose-digesting enzyme, cellulase, beta-glucosidase, and xylan 1,4-beta-xylosidase, in Clostridium group I. Comparing glycoside hydrolase profiles of pandas with those of herbivores and omnivores, we found a moderate abundance of oligosaccharide-degrading enzymes for pandas (36%), close to that for humans (37%), and the lowest abundance of cellulases and endohemicellulases (2%), which may reflect low digestibility of cellulose and hemicellulose in the panda's unique bamboo diet. The presence of putative cellulose-digesting microbes, in combination with adaptations related to feeding, physiology, and morphology, show that giant pandas have evolved a number of traits to overcome the anatomical and physiological challenge of digesting a diet high in fibrous matter.
Callaway, E. Microbes help giant pandas overcome meat-eating heritage, Nature News (17 October 2011) | doi:10.1038/news.2011.596
Tyler, D. Jingjing decoded in part, ARN Literature Blog (28 January 2010)
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