The snow leopard, the agile "ghost of the mountains" that inhabits the rugged ranges of 12 Asian countries, including India, has the lowest genetic diversity of any big cat species in the world, even lower than that of the dwindling cheetah.

A new study led by researchers at Stanford University, published in Proceedings of the National Academy of Sciences (PNAS) on October 7, explained the implications of this phenomenon.

The researchers used whole-genome sequencing data for 37 snow leopards and concluded that the low genetic diversity is, however, "likely due to a persistently small population size throughout their evolutionary history rather than recent inbreeding."

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'Purging' of mutations

This means that "mutations that could potentially cause health issues in snow leopards have been removed from the population over many generations," lead author Katie Solari, a research scientist in biology in Stanford, told The Hindu.

The PNAS paper added: "We found snow leopards to have the lowest heterozygosity of any big cat species, with heterozygosity for every snow leopard sample included in this study falling lower than that observed in any other big cat." This included cheetahs, "which have long been considered the archetype of low heterozygosity in big cats."

The good news is that snow leopards, compared to several Panthera species, have significantly less highly deleterious homozygous load - genes inherited from the mother and father that have fewer instances of duplicated copies of potentially harmful mutations that are connected with health issues.

This, the authors said, suggests effective "purging" of bad mutations during their evolutionary history at small population sizes.

"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," an article in the Stanford Report read.

In fact, "the inbreeding coefficient of snow leopards is significantly higher than other big cats and was even significantly lower than the Asian leopard and puma, indicating that the lower genetic diversity observed in snow leopards is not explained by higher inbreeding," per the research paper.

Dr. Solari told The Hindu that the very low genetic diversity and small population sizes means they may not be able to adapt well to future anthropogenic challenges.

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Critical to Asia's mountains

The wild feline indeed faces a long list of threats today: climate change, habitat loss, decreased availability of primary prey (mountain ungulates such as the Siberian ibex), retaliatory killings for livestock predation, and poaching for their skin. All this while climate change in Asia's high mountain threatens their future. Despite this, snow leopards, which were first listed as 'endangered' were controversially downlisted to 'vulnerable' in 2017 as they did not meet certain criteria for population size.

There are no more than 4,500 to 7,500 individuals, each critical to the Asian mountain ecosystem "that offers immense ecosystem services -- acting as an important source of carbon storage and providing water to almost two billion people."

Hearteningly, however, the international community has worked for decades to establish a sustainable zoo population: in 2008 there were 445 snow leopards across 205 institutions globally, the paper read.

The snow leopard, distinguished by an unusually long tail, which acts as a rudder to help it keep its balance as it traverses its rough terrain, happens to be the least genetically studied of all big cat species. There is, however, evidence of continuous habitat connectivity across at least 75 km in Pakistan and around 1,000 km in Mongolia, and the animal is known to cross long distances between mountain ranges, according to the study.

'Very poorly studies'

As for India, a pioneering survey last year estimated that 718 snow leopards exist in the wild: in Ladakh 477, in Uttarakhand 124, Himachal Pradesh 51, Arunachal Pradesh 36, Sikkim 21, and in Jammu and Kashmir nine. The Indian snow leopard accounts for 10-15 per cent of the global population.

"Of the 12 countries with wild snow leopards, India has the highest numbers after China and Mongolia. That makes India one of the most important countries for the conservation of this species," Kulbhushansingh Suryawanshi, with the India programme of the Snow Leopard Trust at the Nature Conservation Foundation (NCF), Mysore, told The Hindu.

He added that the genetic diversity of leopards in India "is very poorly studied ... We need to sample across the high mountains to understand the genetic diversity of snow leopards in India."

India's Project Snow Leopard, dedicated to the conservation of snow leopards and NGOs such as the NCF, has been working on snow leopard conservation for 27 years, Local community members from snow leopard habitats such as Ladakh, Jammu and Kashmir, Himachal Pradesh, Uttarakhand, Sikkim and Arunachal are key partners in the conservation of snow leopards," said Dr. Suryawanshi.

But the snow leopard in India is threatened by land use change and climate change, he said.

"Almost the entire snow leopard habitat in India is within 50-100 km from the international border. Large-scale infrastructure is changing the face of this region. Climate change-induced warming and floods are impacting the wildlife of this landscape, including the snow leopards to a large extent."

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Maintaining integrity

Dr. Suryawanshi, who is a co-author of the paper, said the main challenge of studying snow leopards is in "getting the samples." Bureaucratic hurdles in getting permissions to study snow leopards generally slow down research, he said.

"In addition, the timelines of funding and permissions often do not match. The Stanford study collaborated with researchers around the world and only then were they able to put together enough samples to make an assessment of the genetic diversity of snow leopards. We need to collect a similar number of samples from within India to understand the genetic diversity of snow leopards in the country."

On the future fate of snow leopards of the fragile high-elevation landscape of the Himalayas, "we need to treat these landscapes and the people that live here with respect," said Dr. Suryawanshi. "The effects of rampant large infrastructure projects are clearly visible in the scale of destruction in the recurrent floods that occur every monsoon."

Maintaining the integrity of the snow leopard's habitat is crucial for the long-term conservation of this charismatic species of the Himalaya, Dr. Suryawanshi added.

Snow leopards are the world's least genetically diverse big cat