There are relatively few snow leopards in the world, and it has likely been that way for a long time, a new study indicates. This situation increases their risk of extinction in a changing environment.
The Stanford-led research, published Oct. 7 in Proceedings of the National Academy of Sciences, found very low genetic diversity among the elusive big cats, who have an estimated population of less than 8,000. They are also highly specialized to their habitat in the arid, mountainous regions of 12 Asian countries, including Russia, Afghanistan, Nepal, and Tibet.
"Snow leopards live in these really untouched areas, unlike other big cat species, which have suffered from human impact already," said first author Katie Solari, a research scientist in biology in Stanford's School of Humanities and Sciences. "They don't have many individuals. They don't have much genetic diversity. Snow leopards are just not well situated to deal with changes that are likely coming their way."
Genetic insights on rarely seen snow leopard
The findings also indicate that snow leopards developed low genetic diversity from having a small, stable population over a long period of time. In contrast, other big cat species, such as the cheetah and Florida panther, are believed to have experienced population crashes, what geneticists call a "bottleneck," that led to their low genetic diversity.
Prior to this research, not much was known about snow leopard genetics. Only four had ever been fully sequenced. This study brings that number to 41, including 35 wild snow leopards and six from zoos around the world.
Achieving that number required years of work and an extensive collaboration with researchers and wildlife officials from 11 countries, all contributing snow leopard blood and tissue samples for analysis at Stanford.
Solari, working with Stanford biologist Dmitri Petrov and colleagues, found evidence that snow leopards not only had low genetic diversity, but also a significantly lower "homozygous load" - meaning that when leopards inherited genes from each parent, there are fewer instances of them having duplicate copies of potentially harmful mutations.
This suggests that over time, snow leopards had a periodic purging of bad mutations in their population: If a negative trait surfaced, those individuals died before reproducing or their progeny were less successful. This purging, facilitated by historic inbreeding, allowed the snow leopard population to remain relatively healthy even at their small numbers.
A snow leopard takes a drink in southern Mongolia. | Snow Leopard Trust and Snow Leopard Conservation Foundation
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When other big cats, such as cheetahs, which once had very large populations, went through a bottleneck, they lost numbers and genetic diversity rapidly. Then, it was harder for them to thrive as more negative mutations were passed down among fewer individuals. Scientists believe cheetahs went through two population bottlenecks that led to their low genetic diversity today and many associated problems, including lower reproductive success and increased disease susceptibility.
Even though snow leopards have been resilient as a small population, that does not mean they will withstand future challenges.
"Because their habitat is so inhospitable, human population growth didn't really affect snow leopards very much, but climate change will," said Petrov, the Michelle and Kevin Douglas Professor in the School of Humanities and Sciences. "Humans don't need to show up in their mountains to build or start agriculture. The climate changes, and it affects everyone and everything, even in such remote areas."
Future challenges
While this study greatly expands genetic knowledge of snow leopards, more research is needed. The team is currently working on analyzing samples from more snow leopards to get a better sense of the population across its entire geographic range.
The researchers have also used this data to develop a genetic test for feces that will allow scientists to learn a lot about wild snow leopards without the need to trap or sedate them. This technology was developed at the Program for Conservation Genomics, founded and led by Petrov. The program applies genetic methods typically used for humans and model research organisms in labs to wildlife to better understand and protect their populations.
This knowledge will inform conservation efforts for snow leopards, which are considered a keystone species in their region. They primarily prey on mountain ungulates, such as the blue sheep of Tibet and the Siberian ibex, as well as smaller mammals, including the pika. The loss of the leopards would indicate the decline of the whole ecosystem, Petrov said.
"If their habitat starts degrading, then snow leopards might go extinct fairly easily, simply because there's just not much ecological space for them and the total population is so small," he said.
