From 6 to more than 240, there is good news for the protection of South China tigers

Many cultures have such a creation myth: after a catastrophe, only one man and one woman are left in the world, and they have to take on the responsibility of reviving the tribe. Although this situation is unlikely to happen to humans today, unfortunately, the situation of some endangered animals is close to this situation.

The more than 240 South China tigers in existence today are all descendants of two males and four females. When inbreeding is inevitable, can we still preserve genetic diversity and breed healthy offspring?

South China tiger at Shanghai Zoo. This tiger subspecies is now extinct in the wild. J. Patrick Fischer / Wikimedia Commons

A recently published study brings us good news: after nearly three decades of efforts and scientific management, the South China tiger population still maintains a moderate level of genetic diversity , and even has two genetically distinct "families" [1].

Sorting out the South China tiger's "family tree"

As recently as the 1950s, there were more than 4,000 South China tigers in China. However, at the time, South China tigers were seen as a threat to humans and livestock and were hunted in large numbers. Coupled with the impact of habitat destruction and fragmentation, the South China tiger population quickly died out in less than 30 years.

In 1979, China banned the hunting of South China tigers, but this did not save the tiger population from falling. Since the 1990s, no South China tiger has been spotted in the wild.

South China tiger hunted in Fujian in 1909 | John C. Caldwell

Captive South China tigers became the hope for saving the South China tiger population. In the 1970s, the six captive South China tigers with breeding records in China came from Shanghai Zoo and Guiyang Qianling Zoo. In the 1970s and 1980s, the captive South China tiger population expanded rapidly, from 13 to 49. But soon, scientists observed the negative effects of inbreeding - the survival rate of cubs was greatly reduced .

In order to save the South China tiger population, the China Zoological Association established the South China Tiger Coordination and Conservation Committee in 1995 to create a "family tree" for the South China tiger and choose individuals with distant blood relations as much as possible when looking for mates for them .

After so many years of efforts, how is the South China tiger population doing now?

What is the “quality” of today’s South China tiger bloodline?

In the recent study, Tu Xiaolong, a doctoral student at the Kunming Institute of Zoology, Chinese Academy of Sciences, Chen Wu, a senior veterinarian at the Guangzhou Wildlife Research Center, and other researchers sequenced the genomes of 29 South China tigers from four major zoos in China and compared them with five other subspecies, including the Siberian tiger and the Bengal tiger.

The Siberian tiger is the largest tiger subspecies. | Svetlana Sutyrina / Wikimedia Commons

The analysis found that the genetic diversity of the South China tiger genome is at a medium level. The research team also identified two genetically distinct South China tiger lineages , corresponding to the two major "families" that belonged to two zoos in the early years.

Moreover, compared with the other two subspecies, the South China tiger genome has the lowest average proportion of harmful mutations on both chromosomes, which means that some genes that are harmful to individual health have been eliminated over time.

Genetic analysis also shows that due to some early hybridization attempts, the South China tigers in Chinese zoos have the bloodlines of Siberian tigers, Indochinese tigers and Bengal tigers, but fortunately there is no obvious genetic contamination . Since 2004, the South China Tiger Coordination and Conservation Committee has sequenced the genomes of all newly born tiger cubs and excluded individuals with too much "foreign" blood from the breeding program to avoid genetic contamination.

When will the jungle king return?

The survival rate of a population is closely related to the level of genetic diversity, and this study can be said to bring good news. " Captive South China tigers are the last hope for this subspecies . We hope that they can be successfully released in the future, repeating the successful case of giant panda conservation and downgrading to 'vulnerable' on the IUCN Red List," the study authors wrote.

South China tiger cubs bred in zoos. Captive South China tigers are the last hope | Tuchong Creative

However, there is still a long way to go to achieve this goal.

How many individuals are required in a population for it to reproduce healthily? The World Conservation Union (IUCN) has adopted the “50/500” rule: at least 50 individuals are needed to combat inbreeding, and at least 500 individuals are needed to retain evolutionary potential [2].

Today’s South China tiger population is still some way from the target of 500, and they are still affected by inbreeding – the mortality rate of South China tiger cubs in the first year of life is as high as nearly 45%, and about 30% of adult females are infertile[3].

The sensational Zhou Tiger incident: In 2007, Zhou Zhenglong used a paper drawing of a tiger to falsely claim that he had photographed a wild South China tiger in Shaanxi. When will a real South China tiger appear in the wild?

Moreover, protecting a species requires much more than the efforts of a small group of professionals. South China tigers are top predators and require a large undisturbed habitat. On the other hand, their historical distribution ranges across 13 provinces in southern China, but a large part of them are now densely populated and economically developed areas. Therefore, in order to rebuild the mountains and forests for South China tigers, it is necessary to carefully coordinate the interests of multiple parties and strike a balance between economic development and nature conservation .

I hope the South China tiger population will prosper and continue to thrive. I hope that by then, our mountains and forests will also be ready to welcome the former king back home.

References

[1] Wang, C., Wu, DD., Yuan, YH. et al. Population genomic analysis provides evidence of the past success and future potential of South China tiger captive conservation. BMC Biol 21, 64 (2023). https://doi.org/10.1186/s12915-023-01552-y

[2] Hvilsom, Christina, et al. "Selecting species and populations for monitoring of genetic diversity." IUCN Publication (2022).

https://portals.iucn.org/library/sites/library/files/documents/2022-023-En.pdf

[3] Charlesworth, D., Willis, J. The genetics of inbreeding depression. Nat Rev Genet 10, 783–796 (2009). https://doi.org/10.1038/nrg2664

Author: Maya Blue

Editor: Mai Mai