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Florida panthers are making a comeback. That's the conclusion a team including UCLA biologists has come to following an attempt at a genetic rescue for the cat that began 30 years ago.

In the 1990s, the Florida panther population was made up of fewer than 30 cats. At the time, they had already been on the endangered species list for nearly two decades, and scientists predicted possible extinction for the species. But in 1995, a handful of panthers from Texas were introduced to try to save the population from inbreeding, which can hasten extinction. Over the years, the Florida panther population has risen to around 200, but the effect of adding the new genetic variation was not known.

The collaboration among several institutions—including UCLA, UC Berkeley and the Florida Fish and Wildlife Conservation Commission—to study the Florida panther genome, in Proceedings of the National Academy of Sciences, has found that local ancestry and genetic variation of Florida panthers have not been replaced by genes introduced from Texas.

"One of the big concerns with bringing in individuals from Texas was that Florida's local genetic variation might get completely replaced," said Diana Aguilar-Gómez, lead author of the study and researcher at UCLA. "That would be a problem if we are trying to preserve the subspecies that's unique to Florida. Our results show that Florida's genetics are still very much present."

What's more, the influx of new genetic variation reduced the influence of harmful mutations that were making it harder for the panthers to survive and reproduce, which is also known as improving the species's fitness. The findings highlight the success of the genetic rescue, but also that its effects might be transient and that continued management of the panthers is needed.

"Our modeling revealed another reason for careful motoring of the Florida panther populations—namely, the effects of translocating individuals can be highly variable and subject to chance, especially looking into the future. The increase in fitness is not guaranteed to be long-lasting," said Kirk Lohmueller, a professor of ecology and evolutionary biology at UCLA, who is co-corresponding author of the study along with Rasmus Nielsen at UC Berkeley.

Florida panthers are a subspecies of mountain lion, which is also called a cougar or a puma. The panthers once lived across Florida, Georgia, Alabama, Mississippi, Louisiana, Arkansas and parts of Tennessee and South Carolina, but habitat destruction and hunting have boxed them into less than 5% of their original territory. Today, they are only found in a few national parks, wildlife preserves and rural areas in South Florida.

As a result of the low population and small territory, individuals had no option but to mate with related individuals, and by the 1990s, the population was showing signs of inbreeding.

How inbreeding threatens the survival of the Florida panther

Inbreeding, which happens when related individuals mate, can make it harder for them to survive and reproduce by allowing harmful genetic mutations to become the default option for various traits. The way it works is that at each position in the DNA sequence, an individual carries two copies of the genetic material. One copy is inherited from their mother and the other from their father. If one of the copies is damaged, the DNA can usually rely on the other copy to compensate.

Any given gene usually comes in numerous variants, called mutations. Most mutations are harmless, such as the genes involved in different eye colors, but if they contain faulty instructions for important biological functions, they can be harmful. When an individual inherits the same mutation from both parents, a condition known as homozygosity, the only option is for that mutation to be expressed. If the instructions contained in the mutation are faulty, there is no way to correct them, and the individual will have the harmful trait.

If, however, an individual only inherits the mutation from one parent and a non-mutated variant from the other parent, a condition called heterozygosity, then often the detrimental mutation may not be expressed.

In Florida panthers, signs of inbreeding include kinked tails and reduced fertility in males. By importing animals from the same panther subspecies that live in Texas, wildlife managers and scientists hoped to reduce inbreeding. But there was a danger that the new genetic variants could swamp or even replace ancestry in the original population.

Even though Florida and Texas panthers are the same subspecies, they live in different areas and do not regularly interbreed, so each population has its own distinct complement of genetic variants, some of which might be tailored to boost survival in their specific environments.

How Texas panthers helped Florida panthers

The new research examined genetic samples from Florida panthers and the five Texas panthers that were known to have produced offspring in Florida, and compared them with samples from mountain lions in California and Brazil. Analysis revealed that the total number of harmful mutations were not reduced by genetic rescue, but the ones in a homozygous state decreased, and heterozygosity increased. This means that harmful mutations are still common in the population, but they are less likely to be expressed and cause problems.

The findings show that conservation measures taken over the past 30 years are working to help Florida panthers survive, but that the endangered species is not out of the woods yet.

"Our simulations suggest that the benefits of the translocation may not last forever," said Aguilar-Gómez. "Right now, harmful mutations are being masked by increased heterozygosity, but if the population stays small—like the current estimate of around 200 panthers—inbreeding could start rising again. This really underscores the need for continued monitoring and management of the Florida panther. Another translocation might be necessary in the future, but that would need to be carefully evaluated and more genetic studies would need to be performed before taking that decision."

Florida panther inbreeding lessons can help with other endangered species, human diseases

The research reinforces the importance of Southern California's Wallis Annenberg Wildlife Crossing over the 101 Freeway for the beloved mountain lions of Los Angeles, which came about from an effort to preserve animal lives and allow greater mobility across the landscape to find mates. California's mountain lions are not endangered, but the population in the Santa Monica Mountains faces habitat destruction and fragmentation and shows signs of inbreeding, such as kinked tails.

This study brought together experts from multiple institutions, including geneticists from UCLA, statisticians and computational biologists from UC Berkeley who simulated the future of the Florida panther, and field biologists with hands-on experience managing and tracking these remarkable animals.