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.

Diet drives convergent evolution of gut microbiomes in bamboo-eating species

Gut microbiota plays a critical role in host physiology and health.The coevolution between the host and its gut microbes facilitates animal adaptation to its specific ecological niche.Multiple factors such as host diet and phylogeny modulate the structure and function of gut microbiota.However,the relative contribution of each factor in shaping the structure of gut microbiota remains unclear.The giant(Ailuropoda melanoleuca)and red(Ailurus styani)pandas belong to different families of order Carnivora.They have evolved as obligate bamboo-feeders and can be used as a model system for studying the gut microbiome convergent evolution.Here,we compare the structure and function of gut microbiota of the two pandas with their carnivorous relatives using 16S rRNA and metagenome sequencing.We found that both panda species share more similarities in their gut microbiota structure with each other than each species shares with its carnivorous relatives.This indicates that the specialized herbivorous diet rather than host phylogeny is the dominant driver of gut microbiome convergence within Arctoidea.Metagenomic analysis revealed that the symbiotic gut microbiota of both pandas possesses a high level of starch and sucrose metabolism and vitamin B12 biosynthesis.These findings suggest a diet-driven convergence of gut microbiomes and provide new insight into host-microbiota coevolution of these endangered species.