Invigorated. Once-inbred Florida panthers are much healthier now thanks to breeding with cougars from Texas.

George Gentry/USFWS

Florida Panthers Dodge Extinction

Fifteen years ago, Florida panthers were in a world of hurt. Only about two dozen of the beleaguered predators roamed in southern Florida, and because of inbreeding they suffered from heart defects, reproductive problems, and other maladies. Scientists calculated that there was a 95% chance that the panthers would die out within 20 years if nothing was done.

Fortunately, something did happen. In 1995, biologists invigorated the panthers with some fresh blood, releasing eight cougars from Texas into south Florida. In the 24 September issue of Science, a comprehensive analysis shows how the genetic reinforcement dramatically improved the health of the panthers. "The key thing that's new is just how striking the increase in [health] was," says biologist Craig Packer of the University of Minnesota, Twin Cities, who wrote a commentary on the findings. But it's also becoming apparent that the panthers aren't out of the woods yet.

By the early 20th century, Florida panthers had been hunted nearly to extinction. By the 1980s, biologists had begun tracking and studying the surviving animals. In 1992, an expert panel of researchers urged that the genetic diversity of the panthers be boosted. After 3 years, the U.S. Department of the Interior brought eight Texas cougars to Florida. (Panthers and cougars are different names for pumas, as are mountain lions in the western United States.)

After the introduction, wildlife managers continued to track the health and numbers of the panthers, the cougars, and their offspring. Stephen O'Brien, a geneticist at the National Cancer Institute's Laboratory of Genomic Diversity in Frederick, Maryland, and colleagues researched the genetic impact.

Some biologists became impatient by the pace of O'Brien's team, however. In 2005, a group led by ecologist Stuart Pimm of Duke University in Durham, North Carolina, collected public data contained in reports from wildlife managers and published an analysis showing that kittens with Texas ancestry were surviving at a rate three times higher than kittens from purebred Florida panthers.

O'Brien's more detailed analysis also shows dramatic improvements. By 2007, the population had risen to about 100. Survival rates were higher for cats with Texas ancestry. Between 2002 and 2004, 21% of the offspring of inbred cats survived, compared with 53% for those with some Texas blood. The prevalence of heart defects in mixed offspring was 8%, half that of purebred Florida panthers. The more genetically diverse animals were also noticeably larger and stronger, O'Brien adds. In all, says conservation biologist Paul Beier of Northern Arizona University in Flagstaff, who was not involved, the paper paints a "dramatic picture of the benefits of genetic restoration."

The panthers' problems are not solved, however. The population is currently only about 130—far lower than the goal of more than 500 needed to maintain a stable, healthy population—and has recently stopped increasing. Moreover, signs of inbreeding are starting to appear again, so the panther population would benefit from additional cougars. "It was only a temporary fix," O'Brien says.