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The giant panda (Ailuropoda melanoleuca) is an iconic bear native to China, famous for eating almost exclusively bamboo. This unusual dietary behavior for a carnivore is enabled by several key adaptations including low physical activity, reduced organ sizes and hypothyroidism leading to lowered energy expenditure. These adaptive phenotypes have been hypothesized to arise from a panda-unique single-nucleotide mutation in the dual-oxidase 2 (DUOX2) gene, involved in thyroid hormone synthesis. To test this hypothesis, we created genome-edited mice carrying the same point mutation as the panda and investigated its effect on metabolic phenotype. Homozygous mice were 27% smaller than heterozygous and wild-type ones, had 13% lower body mass-adjusted food intake, 55% decreased physical activity, lower mass of kidneys (11%) and brain (5%), lower serum thyroxine (T4: 36%), decreased absolute (12%) and mass-adjusted (5%) daily energy expenditure, and altered gut microbiota. Supplementation with T4 reversed the effects of the mutation. This work uses a state-of-the-art genome editing approach to demonstrate the link between a single-nucleotide mutation in a key endocrine-related gene and profound adaptive changes in the metabolic phenotype, with great importance in ecology and evolution.

Parasitic infection as a form of chronic stress affects the cortisol metabolite levels, and the cortisol levels were consistent with the seasonal variation in parasite infection. Sex, age, reproductive status and diet composition were directly associated with helminth parasite richness of wild giant pandas. Age and diet composition had significant influences on the faecal cortisol levels., Many factors, including the inner status of the individuals and external environment, can influence the parasite infections and stress physiology in mammals. Here, we explored the influence of the sex, age, reproductive season and seasonal food availability on the parasitism and stress physiology in wild giant pandas (Ailuropoda melanoleuca) through nutrient and steroid hormone analysis and parasitic infection measurement. Diet composition had significant influences on the faecal cortisol levels and parasite load of wild giant pandas. The seasonal dynamic of the cortisol levels and parasite load in faeces co-vary with the seasonal nutrient intake levels of the pandas, which concurrently arrived the peaks at the wood bamboo shoot-eating period in May (parasite infection intensity, 41.47 ± 12.11 eggs/g of wet faeces; cortisol levels, 619.34 ± 70.55 ng/g dry faeces) that the nutrition intake by wild pandas was the highest (protein/fibre, 69.23 ± 9.93). Meanwhile, age class is also as an important factor to affect the parasite load and stress physiology of wild giant pandas. Cubs and sub-adults suffered more helminth burden and stress physiology than adults and old individuals. This is the first study to evaluate the inner and external factors influence on parasitism and stress physiology in wild giant pandas. The findings facilitate a better understanding of how environmental factors might influence the physiology, behaviour and health of pandas and other species and have implications for the conservation and management of the endangered species.

The giant panda (Ailuropoda melanoleuca) is one of the world's most endangered mammals and remains threatened by environmental and anthropogenic pressure. It is commonly argued that giant pandas are an evolutionary cul-de-sac because of their specialized bamboo diet, phylogenetic changes in body size, small population, low genetic diversity, and low reproductive rate. This notion is incorrect, arose from a poor understanding or appreciation of giant panda biology, and is in need of correction. In this review, we summarize research across morphology, ecology, and genetics to dispel the idea, once and for all, that giant pandas are evolutionary dead-end. The latest and most advanced research shows that giant pandas are successful animals highly adapted to a specialized bamboo diet via morphological, ecological, and genetic adaptations and coadaptation of gut microbiota. We also debunk misconceptions around population size, population growth rate, and genetic variation. During their evolutionary history spanning 8 My, giant pandas have survived diet specialization, massive bamboo flowering and die off, and rapid climate oscillations. Now, they are suffering from enormous human interference. Fortunately, continued conservation effort is greatly reducing impacts from anthropogenic interference and allowing giant panda populations and habitat to recover. Previous ideas of a giant panda evolutionary cul-de-sac resulted from an unsystematic and unsophisticated understanding of their biology and it is time to shed this baggage and focus on the survival and maintenance of this high-profile species.