Giant pandas (Ailuropoda melanoleuca) feed almost exclusively on highly fibrous bamboo, yet they bear a mix of herbivore and carnivore traits. A new study published in the journal Current Biology shows that the macronutrient composition of the diet of giant pandas is similar to that of carnivore diets and unlike that of herbivore diets. This can explain why pandas have adapted incompletely to the plant diet and suggests that their shift to herbivory was easier than it might otherwise seem.
A male giant panda named Xiao Liwu at San Diego Zoo, California, the United States. Image credit: Sci-News.com.
“This study demonstrates the importance of considering both foods and nutrients in understanding the evolutionary ecology of animals — exactly what nutritional geometry is designed to do,” said University of Sydney’s Professor David Raubenheimer, senior author of the study.
Professor Raubenheimer and his colleagues from the University of Sydney and the Chinese Academy of Sciences used nutritional geometry — an approach that considers how mixtures of nutrients and other dietary components influence health and disease, rather than focusing on any one nutrient in isolation — to assess the macronutrient mix of the giant panda’s diet.
They found that the protein and carbohydrate content of the plant-based diet of giant pandas looked more like that of a hypercarnivore — animals that obtain more than 70% of their diet from other animals.
With about 50% of its energy coming from protein, the giant panda’s diet resembled that recorded for feral cats (52%) and wolves (54%). The macronutrient composition of the panda’s milk was also like other carnivores.
“Based on what they eat, giant pandas absolutely belong to the herbivores — but considering the macronutrient composition of the ingested and absorbed diets, they could also belong to the carnivores,” said study lead author Dr. Fuwen Wei, a researcher at the Chinese Academy of Science.
Giant pandas have developed herbivore traits, including a skull, jaw musculature and teeth that are adapted for fibrous diets, and a ‘pseudo-thumb’ used for handling bamboo. They also have lost the ability to taste umami, which is often associated with meat eating.
However giant pandas also have a digestive tract, digestive enzymes, and gut microbes that resemble that of carnivores and not herbivores. This suggests minimal evolutionary modification from their ancestral state was needed to deal with the macronutritional properties of bamboo.
“Our findings can help resolve long-standing questions concerning giant panda evolution, including the unusual transition from carnivorous ancestry to extreme specialized herbivory,” the scientists said.
“In fact, the transition was likely more superficial than assumed, combining substantial adaptation to new food types with relatively smaller changes in macronutrient handling.”
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Yonggang Nie et al. Giant Pandas are Macronutritional Carnivores. Current Biology, published online May 2, 2019; doi: 10.1016/j.cub.2019.03.067
