Mixing up animal populations may be controversial, but it works, say researchers.
The introduction of eight female Texan panthers to an isolated population in Florida may have saved the animals from extinction and improved their genetic health, scientists say. The success of the controversial breeding effort has added weight to the theory that mixing up animal populations is good for the species' survival.
State and federal authorities decided to introduce the Texan panthers in 1995, as it seemed the only way to rescue Florida's subspecies of big cats (Puma concolor coryi). The Florida population was down to an estimated 30 animals at the time, with so much inbreeding that most of the panthers were related to each other. This had resulted in genetic problems such as low sperm counts and testicles that hadn't properly developed, which in turn led to low reproductive success.
The introduction of the Texas subspecies (P. concolor stanleyana) has greatly improved that situation, according to a study due to appear in Animal Conservation in January 2006.
Five of the Texas panthers had offspring with the Florida panthers, and these hybrid kittens were more than three times as likely to survive into adulthood than the pure Florida panthers. They also had fewer genetic abnormalities and were more often seen south of the panthers' usual stomping ground. The population is now up to a healthy 87 individuals, says Stuart Pimm of Duke University in North Carolina, lead author of the study.
"I think this is going to become the poster child for the importance of genetic interference in species management," says Paul Beier, a conservation biologist and panther expert at Northern Arizona University. "It is the strongest story we have yet."
The introduction of the Texas panthers was controversial, Pimm says, in part because researchers thought it would result in the loss of the 'pure' Florida population. Since 1995, however, researchers have realized that the two populations are actually more genetically similar than originally thought. Conservation geneticist Jonathan Ballou of the National Zoological Park in Washington DC says a recent study identified the two as belonging to the same subspecies.
There was also concern that the import of new genes could result in reproductive problems for the hybrid offspring. Previous studies have shown that this can happen when plant or insect subspecies are mixed, for example.
Pimm was initially skeptical himself. There are only a handful of success stories showing that genetic rescue of populations can work, he says, and none of them were with mammals.
Pimm argues that the improved survival of the hybrids is down to the introduction of new genes. But others disagree. David Maehr, a panther expert at the University of Kentucky in Lexington, says the better survival rate of the hybrid animals could still be due to geographical, not genetic, reasons. Most of the hybrids are found further south than the pure breeds, he notes, where the conditions could be different.
Whatever the case, the panther population will probably be stable for a while, Pimm says. But it may be necessary to introduce new genes a few decades from now to ensure that the animals don't become too inbred again.
He adds that this kind of genetic rescue should be a valuable tool for many large mammals facing risk of extinction. "In a sense, that's what this study is about," says Pimm. "It's about lions and tigers and bears and the other big things that are now living in much smaller populations than they once used to be."