The evolutionary adaptation of the giant panda (Ailuropoda melanoleuca) to bamboo diet has taken place by adaptations in its masticatory (chewing) system, according to a new study led by University of Turku scientists.
A special feature in the feeding behavior of the giant panda (Ailuropoda melanoleuca), related to eating bamboo, is the habit to skim the outer green skin of the hard bamboo culm; although the feeding preferences have a seasonal shift, the culm is consumed and skinned during all the year; while eating culm, the outer skin is removed for reasons which until now have remained poorly understood. This image shows a male giant panda named Xiao Liwu at San Diego Zoo. Image credit: Sci-News.com.
“The giant panda has adapted to a herbivorous diet and depends almost exclusively on bamboo,” said University of Turku’s Professor Pekka Vallittu and his colleagues from Finland and China.
“The diversion from omni/carnivorous bears took place during the Late Miocene/Early Pleistocene and was probably associated with the large bamboo resources available at that time.”
“The adaptation process from omni/carnivore to herbivore has resulted in extensive evolution in cranial shape and in the morphology of teeth and dentition.”
“The giant panda also appears not to have evolved a gut microbiota compatible with a bamboo diet,” they said.
“In addition, the obvious deficient in cellulose- and hemicellulose digesting enzymes as well as carnivore-like anatomy of the digestive track have further deepened the ongoing debate around the adaptive pathways of the animal’s evolution towards its newly adopted diet.”
Using modern 3D scanning methods, the researchers studied the movement of the giant panda’s jaw and the structure of its teeth.
They examined the skulls of two giant pandas from the collection of the China Conservation and Research Center for the Giant Panda.
The animals had lived in the wild thereby providing insight into the role of their natural environment in the adaptation of the species to a bamboo diet during evolution.
“Herbivores have usually evolved to have ridged molars that help them grind the plant material and jaws capable of moving sideways which is essential for grinding their food,” the scientists said.
“Although the teeth of giant pandas have been studied extensively, until now, researchers have not paid attention to why the large canines of their upper jaw do not prevent the sideways movement of the lower jaw typical for herbivores — and also humans.”
They found that the panda’s temporomandibular joint differs from those of brown and polar bears.
In addition to the open-closed movement reminding that of a hinge, the joint also allows the jaw to be moved sideways, which is required to peel the bamboo.
Interestingly, this movement isn’t prevented by the large canines the male pandas need to fight.
“The necessity to ensure adequate nutrition has helped evolve the temporomandibular joint and the shape of the teeth to allow efficient peeling of the bamboo without exposing the premolars to the attritive or other damaging effect of bamboo diet,” Professor Vallittu said.
“The evolution of the giant panda’s masticatory system allowed them to be the only large mammals to access an endless source of nutrition in the form of bamboo in the early Pleistocene.”
“The premolars giant pandas use for peeling bamboo are unique among the family of bears and allow the removal of the poisonous green skin of the bamboo which also includes mineral crystals which would wear their teeth,” said Professor Juha Varrela, also from the University of Turku.
“This newly published study is of great scientific significance because it solves the long-prevailing mystery of the ecological interrelationship between the pandas and the bamboo plants,” added Professor Jukka Salo, also from the University of Turku.
The study was published in the journal Scientific Reports.
P.K. Vallittu et al. 2021. Temporomandibular joint and giant panda’s (Ailuropoda melanoleuca) adaptation to bamboo diet. Sci Rep 11, 14252; doi: 10.1038/s41598-021-93808-2