How did “GunGun” turn himself into a “living fossil”?

Do you know the answers to these questions about giant pandas?

How old are giant pandas? How did they survive 8 million years? Why do giant pandas choose to be vegetarians when they are bears? What tricks have giant pandas evolved to eat bamboo?

(Photo source: veer photo gallery)

The national treasure giant panda has a nickname called "GunGun". Don't be fooled by its cute appearance, it has a lot of survival wisdom to be called a "living fossil". According to Chen Qingheng, a researcher at the Ecological Research Center of the Chengdu Institute of Biology, Chinese Academy of Sciences , it is "three ancients": an ancient species, in an ancient habitat, feeding on another ancient species.

Ancient species turn themselves into "living fossils" in "refuges"

"Living fossils" refer to species that have existed in the biological and geological history and have survived to this day. They evolve slowly and still retain their original biological characteristics.

When talking about "living fossils", we have to mention a difficult word: relict organisms, which are living organisms of the same species as fossils discovered today.

Giant pandas have gone through many periods in the natural geological history of evolution. Let's take a look at this long process:

Around 9 to 8 million years ago, in the late Tertiary period, the primitive panda (Ailurarctos) began to appear on Earth.

In the early Pleistocene about 3 million years ago, one of the main branches living in China evolved into a panda that was only half the size of the modern giant panda and was named Ailuropoda micrta. From this time on, the giant panda has evolved into an omnivore that feeds on bamboo .

These small giant pandas went through about 2 million years, and began to expand to the southern forests and adapt to the habitat there. In the middle and late Pleistocene 700,000 to 500,000 years ago, they evolved into the Wulingshan subspecies of giant panda (ailuropoda milanoleuca wulishansis), which is slightly smaller than the modern giant panda, equivalent to about 0.8 to 0.9 times the size of the modern giant panda. Since then, they have become animals that mainly feed on bamboo .

In the late Pleistocene, the giant panda subspecies (ailuropoda milanoleuea daconi) increased in size again, about 1.2 times the size of the modern giant panda, and basically lived on bamboo from then on.

About 12,000 to 11,000 years ago, the cute modern giant panda appeared. The entire distribution area of ​​giant pandas has also retreated from northern China to Southeast Asia to the eastern edge of the Qinghai-Tibet Plateau and the Qinling Mountains, settling in the Minshan Mountain Range, Qionglai Mountain Range, Xiangling Mountain Range in Sichuan, China, the southern slope of the Qinling Mountains in Shaanxi, and some high mountains and deep valleys in southeastern Gansu.

Restoration of the original panda (Photo credit: drawn by Mauricio Antón, provided by the Zhaotong Cultural Relics Protection and Archaeology Institute)

In the past 8 million years, countless animals have become extinct, so why have giant pandas managed to turn themselves into "living fossils"?

Modern giant pandas mainly live in the high mountain canyon area where the eastern edge of the Qinghai-Tibet Plateau transitions to the western edge of the Sichuan Basin, that is, the area where the alpine vegetation area of ​​the Qinghai-Tibet Plateau transitions to the humid forest area of ​​eastern China. This transition zone has undergone many wonderful changes in history. The most important change among them - the impact of the advance and retreat of the ice age - has a lot to do with the survival and reproduction of giant pandas.

The glaciers on the eastern edge of the Qinghai-Tibet Plateau are mountain glaciers. During the ice age, unlike Greenland or Antarctica, the land here is not covered with a large amount of ice and snow, and it does not cause devastating damage to almost all species. In the mountainous areas of western Sichuan, when the ice age comes, the glaciers expand and extend downward along the valleys between the mountains, and the giant pandas and some species also retreat downward; after the ice age (interglacial period), the climate warms and the temperature rises, the mountain glaciers shrink upward along the valleys, and the giant pandas and some species also extend upward along the valleys, that is, they "advance and retreat" with the glaciers.

Therefore, in the western mountains of Sichuan (within the "West China Rain Screen"), animals such as the giant panda, golden monkey, wildebeest, red panda, green-tailed pheasant, golden pheasant, mountain partridge and plants such as Davidia involucrata, yew, licorice tree, and clover have been preserved as rare species. Among them, the giant panda, Davidia involucrata and other animal and plant groups are also called "living fossils."

This lucky place where creatures escaped extinction during the Ice Age is called a "biological refuge" in the history of biological and geological evolution. It is also the place where creatures become active again after the Ice Age and where new species are born, making it the place with the richest biodiversity . The ancient species, the giant panda, has survived hardships and tribulations in such habitats as "biological refuges" and has survived from generation to generation.

It’s obviously a bear, why choose to be a vegetarian?

"Huahua" who eats bamboo (Photo credit: Qiu Yingying)

The ancestors of giant pandas mainly ate meat, which could be said to be at the top of the food chain. Later they became vegetarians, which was also determined by objective conditions.

The early giant panda had sharp canines and carnassial teeth, a short intestine, and the digestive physiology of a carnivore, but it was not as ferocious and agile as other carnivorous animals (such as tigers and leopards). If the source of meat was insufficient, it had to find other food and gradually evolved into a herbivore. Why did it choose bamboo among so many plants?

Herbivores such as rabbits and antelopes are agile in obtaining food, and cattle have rumens to store food and then regurgitate it in a safe environment to digest it slowly. The giant panda has neither such agility nor such an organ structure as a rumen, so it "takes a different approach" and chooses food types that other animals do not eat. It also has some genetic mutations related to eating and digestion, thus forming a unique diet - using arrow bamboo as its staple food, coexisting and co-evolving with it. In the years when bamboo blooms or when it comes to broad-leaved forests and cannot find bamboo and is short of food, it will also eat the younger leaves, tender tips and grass of broad-leaved trees, and even occasionally hunt small animals. However, several species of arrow bamboo in the genus have always been the main food of giant pandas.

The giant panda's choice of a "vegetarian" diet is also related to its ancient habitat. Habitat, also known as habitat, is a general term for the ecology and environment within which a biological population or community lives or resides.

The formation of the giant panda fauna has undergone many complex evolutions of biogeological history and habitat, and finally the cold-temperate subalpine evergreen coniferous forest in the middle of the vertical belt spectrum of the eastern edge of the Qinghai-Tibet Plateau is the main habitat. The cold-temperate coniferous forest is mainly composed of evergreen gymnosperms of the genus Abies and Picea of ​​the Pinaceae family. The building plants include Abies, Abies yunnanensis, Abies scalybark, Abies huangguo, Abies minjiangensis, Picea, Picea lijiangensis, and Picea purpurogena. Gymnosperms, as the ancestors of these plants, can be traced back to the Devonian period between 395 and 345 million years ago. Modern gymnosperms, especially the Abies and Picea plants that constitute the habitat of giant pandas, appeared in the Tertiary period between 65 and 2.6 million years ago and survived the Quaternary glacial period.

Giant pandas choose cold-temperate subalpine evergreen coniferous forests as their habitat, mainly because their habitat attributes are stable and safe. It is cool and humid, which is very comfortable for giant pandas. Subalpine evergreen coniferous forests are the top plant communities in the zonal region and the highest stage of regional vegetation development and succession. Therefore, there is no strong external interference. In addition, it is located in high mountain valleys, and the habitat is relatively harsh, so there are few competitors for giant pandas. According to survey data, the relative abundance of giant pandas in coniferous forest habitats is more than 60%, and the vegetation type that they like to stay and move most is mainly fir forests. This area has the largest continuous population of giant pandas in China.

In order to eat bamboo, what little tricks did the giant pandas use in evolution?

As mentioned above, giant pandas choose to eat "vegetarian" because of some objective conditions. However, in order to eat well and have enough, giant pandas and their food have co-evolved together.

The staple food of giant pandas is bamboo, which is also an ancient plant. The origin of bamboo in the world, especially the biogeological history and geographical distribution evolution of bamboo, is a recognized research difficulty in the international botanical community. After research, Wu Zhengyi, a famous botanist in my country, and others believe that the plants of the Gramineae family (including the subfamily Bambusoideae) originated from the Gondwana continent in the Late Cretaceous. In this way, the origin of bamboo should be no later than 65 million years ago.

Bamboo is the largest subfamily of the monocotyledonous grass family, with about 115 genera and more than 1,500 species worldwide, widely distributed in tropical, subtropical and warm regions. There is an alpine group of bamboos called the genus Fargesia, which exists as the dominant species in the shrub layer of cold-temperate subalpine evergreen coniferous forests. If the fir and spruce trees in the upper tree layer are destroyed, the bamboo in the shrub layer will develop into bamboo thickets according to the path of forest degradation and succession.

As the dominant species and community-building species in the subalpine evergreen coniferous forest shrub layer, the number of individuals of the bamboo is large, the growth density is high, and the bamboo is asexually reproduced, and the iteration speed is fast. Therefore, these characteristics of the bamboo can meet the food needs of the giant panda. The bamboo genus is the basic food of the giant panda and is called the staple bamboo. This is also a result of co-evolution.

According to field survey data, the number of giant panda activity traces in the cold-arrow bamboo (Bashania fangiana) forest is the largest, accounting for 52.92% of the total number of traces in the area, followed by short-cone jade bamboo (Yushania breuipaniculata), accounting for about 17.18%, and third is walking stick bamboo (Fargesia robusta), accounting for about 17.04%. Other types of arrow bamboo that giant pandas often eat include: August bamboo (Chimonobambusa szechuanensis), thorny black bamboo (Chimonobambusa neopurpurea), and western Chinese arrow bamboo (Fargesia nitida).

During the evolution process, giant pandas also worked very hard to eat bamboo, and a series of changes occurred, such as:

1. Change your diet and increase your food intake

Giant pandas were originally omnivores, and their diet should have been similar to that of today's bears. Their intestines are very short, and it is difficult for them to digest bamboo, which has a compact structure, rough fibers, and low nutrients. Therefore, giant pandas spend a lot of time eating a lot of bamboo every day to meet the needs of metabolism and ensure normal body activities. For example, an adult giant panda weighing 100 kilograms will spend 12 to 18 hours a day eating: if it feeds on bamboo stalks, the daily food intake is about 17 kilograms; if it feeds on bamboo leaves, the daily food intake is about 10 to 14 kilograms; if it feeds on bamboo shoots, the daily food intake is about 40 kilograms.

2. Radius evolution

During the evolution process, the giant panda's body shape and diet were not able to adapt to the new habitat changes, and it should have become extinct along with the saber-toothed elephants and saber-toothed tigers of the same era. However, the giant panda's omnivorous nature saved it and made it more and more enthusiastic about herbivory. In order to further adapt to eating arrow bamboo, the giant panda evolved a bone called the radial sesamoid bone on its wrist, which enables it to better grasp the bamboo pole and not slip.

Giant pandas grasping and chewing bamboo (Photo by Sharon Fisher, courtesy of Wang Xiaoming)

3. Other changes

Giant pandas have also evolved an astonishingly low metabolic rate to adapt to the ultra-low energy acquisition rate brought by bamboo, including a genetic mutation that makes meat unappetizing. This is also the result of the giant pandas gradually developing a special biological and ecological learning habit of eating arrow bamboo as their staple food, after they evolved a tendency to eat bamboo.

Fargesia spathacea Franch

Conclusion

Do you understand the survival wisdom of “GongGong” now?

Giant pandas live in a natural habitat of subalpine coniferous forest vegetation type composed of cold-temperate spruce plants preserved in the Tertiary Period, eating grass bamboo plants left over from the Tertiary Period, and finally successfully survived for 8 million years . This is a unique and rare biogeographic community landscape map, not only a coincidence of biological evolution, but also a masterpiece!

Author: Qiu Yingying

Author unit: Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu Branch of Chinese Academy of Sciences

Special thanks to: Chen Qingheng, Researcher at the Ecological Research Center, Chengdu Institute of Biology, Chinese Academy of Sciences

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