Convergent gut microbial functional strategies drive energy metabolism adaptation across Ursidae species and challenge the uniqueness of giant panda.

The gut microbiota is a key regulator of host energy metabolism, but its role in seasonal adaptation and evolution of bears is still unclear. Although giant pandas are considered an extraordinary member of the Ursidae family due to their specialized herbivory and low metabolic rate, there is still controversy over whether the metabolic regulation mechanism of their gut microbiota is unique. This study analyzed the seasonal dynamics of gut microbiota in giant pandas (Ailuropoda melanoleuca), Asian black bears (Ursus thibetanus), brown bears (Ursus arctos), and polar bears (Ursus maritimus), and combined with fecal microbiota transplantation (FMT) experiments, revealed the following findings. The microbial composition of the four bear species is similar, with both Firmicutes and Proteobacteria dominating. The enrichment of Firmicutes in winter enhances lipid metabolism, and adapts to dietary differences, indicating the existence of convergent microbial functional strategies in the Ursidae family. Our results demonstrate that bear gut microbiota promoted seasonal adaptation. In FMT experiments, bear gut microbiota in winter may had stronger functional capabilities on regulating host energy metabolism in mice, and regulate host appetite to increase energy intake. Finally, despite feeding on bamboo, giant pandas microbiota driven energy metabolism pathways (such as SCFAs) are highly conserved compared to other bears, suggesting a deep commonality in the adaptability of bear microbiota in evolution. Therefore, this study challenges the traditional view of microbial uniqueness of giant pandas, and emphasizes the co-evolutionary mechanism of energy metabolism adaptation in bear animals through microbial plasticity. In the future, it is necessary to integrate wild samples to eliminate the interference of captive diet and further analyze the genetic basis of host gut microbiota interactions.