Breeding rare Florida panthers with Texas cougars created tough hybrids that one scientist calls the Arnold Schwarzeneggers of cougars.

And, like action heroes, these vigorous offspring may well rescue the Florida subspecies from extinction, according to Stephen O'Brien, an animal geneticist who co-authored new research on the North American big cat.

Florida panthers are considered a subspecies of cougar, big cats found across the Americas that are also called pumas or mountain lions, depending on the region.

In the 1900s people hunted the Florida panther out of most of its southeastern U.S. range, driving the few remaining animals into rugged South Florida swamps.

Inbreeding within this tiny population caused heart problems and reproductive defects that would have killed off the Florida panther—deemed endangered by the U.S. Fish and Wildlife Service—by the early 21st century.

As a last-ditch effort, in 1995 the U.S. government released eight female cougars from a wild Texas population into Florida.

This cougar infusion increased the number of Florida panthers threefold, to about a hundred, said O'Brien, chief of the Laboratory of Genomic Diversity at the National Cancer Institute in Frederick, Maryland.

In addition, the offspring produced were genetically diverse animals that were stronger and lived longer, the 30-year study revealed.

Texas Cougars Shuffled Genetic Deck

Since the early 1980s, O'Brien and colleagues have closely monitored several Florida panthers via radio transmitters and microchips, occasionally anesthetizing animals to take blood samples. Those samples revealed a "marked increase" in DNA diversity after the Texan animals were introduced.

The team also measured survival rates of kitten litters and adult cats. (See pictures of Florida panther kittens.)

For instance, 23 out of 29 Florida panthers surveyed that were older than a year died between 2002 and 2004, compared with just 22 out of 47 hybrids, according to the study, published today in the journal Science.

The scientists also measured the animals' fitness, or ability to survive. One unusual measure of fitness, O'Brien noted, involved recording how a cougar reacted when the animal attempted to escape scientists' capture by climbing up a tree.

Most Florida panthers would cower in the tree. But trapped hybrids were more than twice as likely than Florida panthers to leap out of the tree and sail over the scientists' heads to safety, he said.

"Virtually every measure," he said, "showed the animals that had the mixed ancestry did better."

In a sense, releasing the Texan cougars restored the genetic flow that humans had interrupted, O'Brien added. In the 19th century, Florida panthers would sometimes mate with western cougars, naturally "shuffling the deck" genetically, he said.

"We don't feel like we've fiddled so much with nature, like making a hybrid between a lion and a tiger." (See pictures of real-life "ligers.")

Florida Panthers Not Out of the Woods

In general, the research shows that bringing in new genes to aid a failing population "can be deliriously successful," O'Brien said.

"It's really not rocket science—if you have enough habitat and don't inbreed much, millions of years of evolution have given these species what it takes to survive and to prosper."

Even so, conservationists can't yet say hasta la vista to the Florida panther's problems.

"It was a very bold experiment and it has clearly paid off," said Elizabeth Fleming, Florida representative for the nonprofit Defenders of Wildlife.

But "now is the biggest challenge of all: We need to conserve existing habitat for these animals, as well as allow them to expand into some areas of their former range."

A hundred animals do not make up a truly viable population—for the subspecies to make it, their range needs to be expanded into other parts of Florida, Fleming said.

To that end, her organization is working with landowners to buy conservation easements, which would allow the predators to move onto land dedicated solely as wildlife habitat.

Meanwhile, some male Florida panthers are already striking out into new territory themselves, Fleming noted. (See "Cougar Reports on the Rise in Eastern U.S.")