Genetic studies of South China tiger populations show that the genetic diversity of the existing South China tiger population is at a medium level and has good population recovery potential.
The South China tiger population is hopeful.
◎Intern reporter Li Zhaoyu
"The sawtooth hook and claw are as sharp as a blade, and a whistling cold gives rise to a thousand winds." Since ancient times, tigers, especially South China tigers, have been loved and concerned by Chinese because of their mighty appearance and profound cultural significance.
However, in the past hundred years, with the destruction of habitats and the impact of poaching, the South China tiger has almost disappeared in China, and it is difficult to find tigers in the wild. Fortunately, thanks to timely protection, the South China tiger was able to thrive in the zoo's captivity, without following in the footsteps of Caspian tigers, Bali tigers and Javan tigers.
The survival of the national tiger is by no means "God blessed", behind this, in fact, is the unremitting efforts of animal protection workers for decades.
Not long ago, a good news related to South China tigers came: Tu Xiaolong, a doctoral student at the Kunming Institute of Zoology, Chinese Academy of Sciences, Chen Wu, a senior veterinarian at Guangzhou Zoo (Guangzhou Wildlife Research Center), and other researchers sequenced the genomes of 4 South China tigers from four major zoos. Studies have shown that after nearly 29 years of hard work and scientific management, the South China tiger population still maintains a moderate level of genetic diversity, and even two "families" with obvious genetic differences have emerged. On April 30, the paper was published in BMC Biology.
Experts believe that this study shows that the protection of South China tigers may usher in a new dawn. As long as the time is ripe, the tiger roaring mountain forest can be expected.
South China tiger population recovery potential is good
As the only tiger subspecies exclusively produced in China, the South China tiger has been widely distributed in Guangdong, Hunan, Jiangxi, Guangxi and other places. In the 20s of the 50th century, there were thousands of tigers in South China in China, and even the so-called "tiger plague" was formed in some areas.
Fundamentally speaking, the "tiger plague" is a conflict caused by people and tigers competing for land. Historically, such conflicts have existed. The legends and stories such as "Dian Wei chasing the tiger across the stream" and "Wusong fighting the tiger" are the embodiment of this conflict. However, with the rapid expansion of population and the rapid development of productivity in the past hundred years, the conflict between people and tigers has intensified. Ultimately, habitat loss and hunting behaviors caused by the expansion of human land have led to fewer South China tigers surviving in the wild.
"At present, there are more than 200 captive South China tigers in domestic zoos, all of which are the descendants of one male tiger and two female tigers from Guizhou Province in Guiyang Qianling Park, one male tiger and one female tiger from Guizhou Province and one female tiger from Fujian Province in Shanghai Zoo." Wang Chen, co-first author of the paper and doctor of Guangzhou Zoo (Guangzhou Wildlife Research Center), told reporters.
Since the extant captive South China tiger is the descendant of six individuals, people can't help but wonder: Is the South China tiger, like big cats such as cheetahs, in a situation where it is difficult to survive due to extremely inbreeding populations? "This study shows that this does not exist." Tu Xiaolong, co-corresponding author of the paper, said.
Tu Xiaolong introduced that in this study, the researchers used high-throughput sequencing technology to assemble a high-quality reference genome of South China tiger at the chromosome level, which provides an important basis for future functional research and genetic protection of South China tiger genes.
"Using the assembled reference genome, we resequenced the whole genome of 29 captive South China tigers, and combined with the genome data of more than 6 individuals of six tiger subspecies such as Sumatran tigers, Siberian tigers and Bengal tigers available on the Internet, we calculated that the genetic diversity of South China tigers is not the lowest among these subspecies." Tu Xiaolong said, "Through the analysis of the genetic structure of the population, we found that there are two 'families' in the existing captive South China tiger population, namely the Shanghai line and the Guiyang lineage. We also found that the current South China tiger population contains almost no descent from other tiger subspecies, suggesting that the captive South China tiger population has been quite successfully protected over the past few decades. ”
Tu Xiaolong further pointed out that the overall level of homozygous regions in the genome of South China tigers is high, and this high inbreeding phenomenon should be the result of inbreeding of six captive South China tigers in the past 60 years. "However, compared with the data of the remaining five tiger subspecies, the proportion of homozygotes with high and medium harmful mutations in the genome of South China tigers was significantly lower than that of other tiger subspecies, indicating that the genome of South China tigers is undergoing the process of clearing the genetic load of homozygous for high and medium harmful mutations." Tu Xiaolong said, "In layman's terms, although inbreeding objectively exists, the genome of the South China tiger is tenaciously 'self-healing', and the results are very remarkable." ”
Genetic studies of South China tiger populations show that the genetic diversity of the existing South China tiger population is at a medium level and has good population recovery potential.
The South China tiger population is hopeful.
Technology helps protect South China tigers
Studies show that there are currently only two main "families" of South China tigers, Shanghai and Guiyang, how did this conclusion come about?
Wang Chen introduced that the researchers used SNP sites in the whole genome to analyze the genetic structure of the population, and found that the construction of phylogenetic trees and the analysis of Admixture software showed that the current captive South China tiger population is divided into two branches (Shanghai and Guiyang lineage two ancestral genetic backgrounds) and mixed individuals with both genetic backgrounds. This study unravels the mystery of the two existing "families" of captive South China tigers.
"Due to the small number of ancestors of captive South China tigers, even if the China Zoo Association China South China Tiger CCP (First-level Management Project) working group established a cooperative breeding mechanism for captive South China tigers, the exchange of breeding germplasm between captive South China tiger groups is still relatively limited. Over the decades, genetic drift has led to the natural formation of two 'families' of South China tigers. Wang Chen said, "Based on the conclusions, we should further strengthen the genetic exchange between the two South China tiger populations, avoid higher inbreeding in small populations, and maintain the genetic diversity of South China tiger populations to the greatest extent." ”
In addition to the use of traditional breeding control methods to improve genetic diversity, in recent years, gene editing, irradiation, mutagenic drugs and other emerging scientific and technological means have also attracted people's attention. So, are these means feasible?
According to Lai Liangxue, a researcher at the Guangzhou Institute of Biomedicine and Health of the Chinese Academy of Sciences, the answer is clearly no. "It is theoretically feasible to use the above methods to change the genetic sequence of South China tigers to achieve the purpose of increasing diversity, but it is still not feasible overall." Lai Liangxue said, "The changes in animal genes by irradiation and mutagenic drugs are random and uncontrollable, which may induce abnormal phenotypes, but will cause serious harm to endangered animals, so it is not suitable for implementation on endangered animals; As far as gene editing is concerned, the current level of technology requires a large number of fertilized eggs and surrogate tigresses of South China tigers to be carried out, which requires that the test animals have a certain population size, and it is impossible to apply to South China tigers with only more than two hundred tigers. ”
Lai Liang said that although the above means are not feasible, other scientific and technological means can effectively help protect South China tigers. "For example, through induced pluripotent stem cell technology, we can induce mature somatic cells of South China tigers into stem cells, and then use the pluripotency of stem cells to differentiate into sperm or eggs, thereby improving the reproductive ability of South China tigers." "We have collaborated with Guangzhou Zoo on relevant research, but there are still many technical details to be explored. ”
Multi-party cooperation to make South China tiger "tiger and tiger prosperous"
Chen Wu, co-corresponding author of the paper, introduced that the China Zoo Association was fully aware of the necessity of rescue protection of South China tigers as early as the 20s and 1995s of the <>th century, and established the South China Tiger Protection Coordination Committee in <>. The committee manages the South China tigers scattered in zoos across the country as a single population, and uniformly deploys seed sources for cooperative breeding to avoid inbreeding. After that, the committee also established the pedigree book of South China tigers, carried out scientific matching management of South China tigers, and carried out research work such as semen assessment of South China tigers, artificial feeding technology of South China tigers, individual identification of genetic contamination of South China tigers, prevention and control of important diseases of South China tigers under the coordination and organization of the China Zoo Association, etc., and solved a series of major problems in captivity breeding. The relevant departments have also screened some outstanding South China tiger individuals and sent them to Meihuashan in Fujian Province and South Africa to carry out rewilding training, and have made some progress.
"Through generations of hard work, the South China tiger population has finally grown from six to more than 6." Chen Wu said with satisfaction, "This study confirms that the genetic management of the South China tiger population has been effective before. ”
Chen Wu said that in the rescue and protection of South China tigers, there are still many problems that need to be tackled and overcome.
"Needless to say, in the 60 years of rescue conservation of South China tigers, although we have made great achievements. But problems with inbreeding decline, such as lower cub survival, have been identified in populations. "We need to analyze and study some homozygous lethal recessive genes and mutation rates in the genome of South China tigers, so as to better elucidate the mechanism of inbreeding decline of South China tigers, and accurately guide reproductive pairings at the genetic level to promote the conservation and management of South China tigers." ”
Experts agreed that a germplasm resource bank of South China tigers should be established to construct a genome map of South China tigers to preserve and record the genetic information of South China tigers more comprehensively.
"In addition, by establishing an individual genome database, we can scientifically conduct health management, disease prevention and breeding guidance." Tu Xiaolong pointed out.
Chen Wu believes that a continuous, vast and resource-rich habitat habitat is essential for the survival of the South China tiger. Habitat habitat restoration is a key element for the rejuvenation of wild populations. Therefore, to protect the South China tiger, we must first protect the natural environment on which it depends.
"Our biggest goal in captivity is to provide quality seed sources for wild populations. On the one hand, we should strengthen the prevention and control of South China tiger diseases and ensure the health of South China tiger populations; On the other hand, we should strengthen the management of the South China tiger population to ensure the sustainable development of the South China tiger population; Most importantly, the society and the public should fully recognize the importance of South China tiger conservation to ecological civilization construction and biodiversity conservation, strengthen the investment of funds, facilities and human resources, further improve management measures, especially strengthen the mobile management of individual South China tigers, and facilitate the cooperative breeding of South China tigers of appropriate age between conservation institutions. Chen Wu said, "I believe that with the joint efforts of all parties, South China Tiger will definitely usher in a better tomorrow!" (Source: Science and Technology Daily)