Thriving hybrid salamanders contradict common wisdom

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 professor Bradley Shaffer, was published recently in the Proceedings of the National Academy of Sciences' online edition.

The salamander experts studied the survival rates and genetic makeup of three types of salamanders: native California tiger salamanders (Ambystoma californiense), which are protected under the U.S. Endangered Species Act; barred tiger salamanders that were introduced in California from Texas in the 1950s (Ambystoma tigrinum mavortium); and the hybrid offspring born when the two species mated. They 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 vigour' is largely limited to plant crosses).

That raises difficult questions for managing endangered native salamander populations, Shaffer said. Some conservationists might say that hybrids are an acceptable change, since they are favoured by natural selection, and 'improve' the original species. 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 humans both create new opportunities for hybridisation with introduced species, and improve the genetic analyses that detect them.