[Photo] A chart showing the two natural salamander species and the hybrid offspring. Credit: National Science Foundation

A hybrid of two salamander varieties???one of which is an endangered species???is outshining both if its slimy parents' purebred offspring in the game of life.

Breeding between endangered California tiger salamanders and the invasive barred salamanders, commonly used as fishing bait and introduced decades ago, has created swarms of new salamanders.

The hybrid salamanders are infertile, but researchers have discovered they're more likely to survive than either parent species. The competitive debacle is causing some scientists to reconsider the supposedly weak role of such hybrids in the course of evolution.

The two species have evolved independently for millions of years and are about as genetically different from one another as are humans and chimpanzees, the researchers said.

"The mixture of genes from organisms that are distinct enough to be called separate species don't usually produce healthy, fit offspring," said Benjamin Fitzpatrick, an evolutionary biologist at the University of Tennessee in Knoxville.

Ecologists are concerned the hybrids are pushing the California tiger salamander closer to the brink of extinction, calling the study "one of the first demonstrations of this threat."

The researchers don't know why the hybrids are thriving. "The hybrids could be more resistant to disease, better able at escaping predators, or more efficient at gathering food than their parent species," Fitzpatrick said.

A study of the salamander crossbreed is detailed in a recent issue of the The Proceedings of the National Academy of Sciences.