A new UC Davis study not only has important findings for the future of California tiger salamanders, but also contradicts prevailing scientific thought about what happens when animal species interbreed.

The study, by former UC Davis doctoral student Benjamin Fitzpatrick (now on the faculty of University of Tennessee, Knoxville) and evolution and ecology professor Bradley Shaffer, was published recently in the online edition of the Proceedings of the National Academy of Sciences.

The salamander experts studied the survival rates and genetic makeup of three species: native California tiger salamander (Ambystoma californiense), protected under the U.S. Endangered Species Act; barred tiger salamander, introduced in California from Texas in the 1950s (Ambystoma tigrinum mavortium); and the hybrid offspring of the California tiger salamander and the barred tiger salamander.

The researchers found that more of the hybrid young survived in the wild than did young of the native or the introduced species -- quite a surprise, since animal hybrids are usually less fit than their parents ("hybrid vigor" is largely limited to plant crosses).

That raises difficult questions for managing endangered native salamander populations, Shaffer said, echoing the study's title: "Hybrid Vigor Between Native and Introduced Salamanders Raises New Challenges for Conservation."

"Some conservationists might say that hybrids are an acceptable change, since they are favored by natural selection, and "improve" the original species, Shaffer said. Others might consider hybrids to be genetically impure and regard them as threats to the native salamanders, their competitors and their prey.

Such questions will arise more frequently, Shaffer said, as people create new opportunities for hybridization with introduced species, and improve the genetic analyses that detect them.

On the Net: www.pnas.org