Lineage-specific evolution of bitter taste receptor genes in the giant and red pandas implies dietary adaptation.

Taste 2 receptors (TAS2R) mediate bitterness perception in mammals, thus are called bitter taste receptors. It is believed that these genes evolved in response to species-specific diets. The giant panda (Ailuropoda melanoleuca) and red panda (Ailurus fulgens styani) in the order Carnivora are specialized herbivores with an almost exclusive bamboo diet (>90% bamboo). Because bamboo is full of bitter tasting compounds, we hypothesized that adaptive evolution has occurred at TAS2R genes in giant and red pandas throughout the course of their dietary shift. Here, we characterized 195 TAS2R genes in 9 Carnivora species and examined selective pressures on these genes. We found that both pandas harbor more putative functional TAS2R genes than other carnivores, and pseudogenized TAS2R genes in the giant panda are different from the red panda. The purifying selection on TAS2R1, TAS2R9 and TAS2R38 in the giant panda, and TAS2R62 in the red panda, has been strengthened throughout the course of adaptation to bamboo diet, while selective constraint on TAS2R4 and TAS2R38 in the red panda is relaxed. Remarkably, a few positively selected sites on TAS2R42 have been specifically detected in the giant panda. These results suggest an adaptive response in both pandas to a dietary shift from carnivory to herbivory, and TAS2R genes evolved independently in the 2 pandas. Our findings provide new insight into the molecular basis of mammalian sensory evolution and the process of adaptation to new ecological niches.

Shan L ，Wu Q ，Wang L ，Zhang L ，Wei F ... -  《Integrative Zoology》

Comparative genomics reveals convergent evolution between the bamboo-eating giant and red pandas.

Hu Y ，Wu Q ，Ma S ，Ma T ，Shan L ，Wang X ，Nie Y ，Ning Z ，Yan L ，Xiu Y ，Wei F ... -  《-》

Potential Mechanism of Detoxification of Cyanide Compounds by Gut Microbiomes of Bamboo-Eating Pandas.

Gut microbes can enhance the ability of hosts to consume secondary plant compounds and, therefore, expand the dietary niche breadth of mammalian herbivores. The giant and red pandas are bamboo-eating specialists within the mammalian order Carnivora. Bamboo contains abundant plant secondary metabolites (e.g., cyanide-containing compounds). However, Carnivora species, including the giant panda, have deficient levels of rhodanese (one of the essential cyanide detoxification enzymes) in their tissues compared with the same tissues of herbivores. Here, we make a comparative analysis of 94 gut metagenomes, including 25 from bamboo-eating pandas (19 from giant pandas and 6 from red pandas), 30 from Père David's deer, and 39 from published data for other mammals. The bamboo-eating pandas' gut microbiomes had some common features, such as high proportions of Pseudomonas bacteria. The results revealed that bamboo-eating pandas' gut microbiomes were significantly enriched in putative genes coding for enzymes related to cyanide degradation (e.g., rhodanese) compared with the gut microbiomes of typical herbivorous mammals, which might have coevolved with their special bamboo diets. The enrichment of putative cyanide-digesting gut microbes, in combination with adaptations related to morphology (e.g., pseudothumbs) and genomic signatures, show that the giant panda and red panda have evolved some common traits to adapt to their bamboo diet.IMPORTANCE The giant panda (Ailuropoda melanoleuca) and red panda (Ailurus fulgens), two obligate bamboo feeders, have distinct phylogenetic positions in the order Carnivora. Bamboo is extraordinarily rich in plant secondary metabolites, such as allied phenolic and polyphenolic compounds and even toxic cyanide compounds. Here, the enrichment of putative cyanide-digesting gut microbes, in combination with adaptations related to morphology (e.g., pseudothumbs) and genomic signatures, show that the giant panda and red panda have evolved some common traits to adapt to their bamboo diet. Thus, here is another story of diet-driven gut microbiota in nature.

Zhu L ，Yang Z ，Yao R ，Xu L ，Chen H ，Gu X ，Wu T ，Yang X ... -  《mSphere》

Gene expressions between obligate bamboo-eating pandas and non-herbivorous mammals reveal converged specialized bamboo diet adaptation.

It is inevitable to change the function or expression of genes during the environmental adaption of species. Both the giant panda (Ailuropoda melanoleuca) and red panda (Ailurus fulgens) belong to Carnivora and have developed similar adaptations to the same dietary switch to bamboos at the morphological and genomic levels. However, the genetic adaptation at the gene expression level is unclear. Therefore, we aimed to examine the gene expression patterns of giant and red panda convergent specialized bamboo-diets. We examined differences in liver and pancreas transcriptomes between the two panda species and other non-herbivorous species. The clustering and PCA plots suggested that the specialized bamboo diet may drive similar expression shifts in these two species of pandas. Therefore, we focused on shared liver and pancreas DEGs (differentially expressed genes) in the giant and red panda relative to other non-herbivorous species. Genetic convergence occurred at multiple levels spanning carbohydrate metabolism, lipid metabolism, and lysine degradation. The shared adaptive convergence DEGs in both organs probably be an evolutionary response to the high carbohydrate, low lipid and lysine bamboo diet. Convergent expression of those nutrient metabolism-related genes in both pandas was an intricate process and subjected to multi-level regulation, including DNA methylation and transcription factor. A large number of lysine degradation and lipid metabolism related genes were hypermethylated in promoter regions in the red panda. Most genes related to carbohydrate metabolism had reduced DNA methylation with increased mRNA expression in giant pandas. Unlike the red panda, the core gene of the lysine degradation pathway (AASS) doesn't exhibit hypermethylation modification in the giant panda, and dual-luciferase reporter assay showed that transcription factor, NR3C1, functions as a transcriptional activator in AASS transcription through the binding to AASS promoter region. Our results revealed the adaptive expressions and regulations of the metabolism-related genes responding to the unique nutrients in bamboo food and provided data accumulation and research hints for the future revelation of complex mechanism of two pandas underlying convergent adaptation to a specialized bamboo diet.

Ma J ，Zhang L ，Shen F ，Geng Y ，Huang Y ，Wu H ，Fan Z ，Hou R ，Song Z ，Yue B ，Zhang X ... -  《BMC GENOMICS》

Comparative Transcriptomics and Methylomics Reveal Adaptive Responses of Digestive and Metabolic Genes to Dietary Shift in Giant and Red Pandas.

Li L ，Shen F ，Jie X ，Zhang L ，Yan G ，Wu H ，Huang Y ，Hou R ，Yue B ，Zhang X ... -  《Genes》