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Tiger, lion and domestic cat genes not so different

Genomes of big felines provide insight into their evolution

DNA DONATION  HwaRang, a white Bengal tiger that lives at the Everland Zoo in South Korea, is one of five big cats that donated DNA for a genome sequencing project.
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Tigers and their relatives have hit on the right combination of genes to make them successful hunters, scientists have learned from studying the DNA of some of the biggest big cats.

Along with teasing out the Siberian tiger’s secrets, an international team of scientists also examined the genomes of a white Bengal tiger, a snow leopard and two African lions, one of them from a rare white female. The vulnerable and endangered animals’ genomes, reported September 17 in Nature Communications, are the start of a database that is important for understanding the cats’ evolutionary past and for preserving their future, says Lisette Waits, a conservation geneticist at the University of Idaho, who was not involved in the study. “It’s impressive, exciting work,” she says.

Already the project is shedding light on how tigers, lions and snow leopards became top-tier predators and adapted to wildly different environments.

All present cat species last shared a common ancestor about 11 million years ago. Usually genomes get scrambled as species evolve, says Jong Bhak, a bioinformatician at the Genome Research Foundation in Suwon, South Korea, who was one of the study leaders. But when the team compared the genome of a 9-year-old Siberian tiger named TaeGeuk to that of domestic cats, the researchers found few big differences. That probably means that cats both big and domestic “are very well adapted, successful evolutionary machines,” Bhak says.

But many subtler changes set big cats apart from other animals. Big cats share 1,376 genetic changes not found in other animals and people, the researchers discovered. Among those genes are many related to digesting meat – not a surprise, Bhak says, given that cats are obligate carnivores. Genes involved in muscle strength, sense of smell, visual perception and nervous system development are evolving rapidly in Siberian tigers, the team found.

Snow leopards displayed two mutations that may help them live high in the mountains of central Asia, where oxygen is in short supply. Different changes in the same genes, called EGLN1 and EPAS1, have been credited with helping Tibetan people adapt to live at high altitudes. And naked mole rats, which also live with little oxygen, carry yet another alteration to one of those genes.

Leopards aren’t the only copycats. The DNA of an African white lion and white Bengal tiger revealed that both cats’ pale coats are due to mutations in a gene that also gives some domestic cats white fur. That gene, called TYR, contains a mutation in the white tigers different from the one that bleaches the coats of white lions.

The data can help scientists monitor genetic diversity and aid in conservation efforts, Waits says. Snow leopards have low levels of genetic diversity, the researchers found, nearly half that of the other big cat species. Low genetic diversity can be a sign that a species is heading toward extinction.

Cats in general have low levels of diversity, says Marcella Kelly, a population ecologist at Virginia Tech. “I get more worried if an animal has lost diversity recently,” she says. The researchers have DNA of only one snow leopard, so they don’t know whether the animals naturally have low levels or if their genetic diversity has taken a dive.

Editor's note: This story was updated on September 26, 2013, to clarify that some of the big cats in the study are classified as vulnerable, not endangered.

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