Salamander study challenges conservation logic
Posted on September 19th, 2007By Lauren Morello
E&E News: Chance matings between a threatened California salamander and an invasive species have produced offspring with better survival skills than either parent — a result that the study’s authors say challenges the notion that preserving native species is always the best outcome for conservation efforts.In many instances, hybrid animals, produced when two distinct species mate, are less fit than their parents.
But that is not true for offspring of the threatened California tiger salamander and the invasive barred tiger salamander, which have been mixing in California’s Salinas Valley for the last 50 to 60 years, since anglers imported the barred salamanders from Texas for use as bait.
Hybrid larvae produced in five mixed breeding populations in the Salinas Valley are more likely to survive the critical first weeks of life than larvae from either the threatened native salamanders or the invaders, according to research that will be published online this week in Proceedings of the National Academy of Sciences.
The study documents the first known case where a hybrid species is outcompeting its threatened parent. That is a surprising result because the California tiger salamander and the barred tiger salamander have been geographically separate for about 5 million years, said lead author Benjamin Fitzpatrick, an evolutionary biologist at the University of Tennessee.
To put that in perspective, the 5 million year gap has left the two salamander varieties “about as distinct as humans are from chimps,” he said.
Overall, between 15 to 20 percent of the salamanders in each of the populations studied turned out to be hybrids, concluded Fitzpatrick and co-author Bradley Schaffer of the University of California-Davis.
The result raises questions about when a native species should be protected from mixing with an invasive one, Fitzpatrick said.
“The challenge is whether we want to simply think of hybridization as bad, because the pure native thing is what we want to protect,” he said. “Or do we want to establish some tolerance” — to allow a mixed, possibly genetically superior population to thrive.
‘Case-by-case’
As it now stands, hybridization is not explicitly addressed by the Endangered Species Act, and the Fish and Wildlife Service does not have an official policy on the matter, agency spokeswoman Valerie Fellows said. Instead, FWS treats the issue on a “case-by-case” basis, she said.
In the case of the California tiger salamander, hybridization was considered a major concern in decisions to list various populations as threatened.
But there have also been well-known cases where endangered species have been mated with close relatives to avoid near-certain extinction, including a successful effort in the early 1990s to breed endangered Florida panthers with Texas cougars, experts said.
But they argued that the situation with the salamanders is different, as there are still significant numbers of the native California species that could be increased if the invasive barred animals were reduced.
“It all depends on the threat level,” said Kieran Suckling, policy director for the Center for Biological Diversity, which successfully sued the federal government to force protection for the native salamanders.
“Invasive species are the second leading cause of extinction,” he said. “In almost every case the reason the invasives cause natives to go extinct is because the invasives can do better in the habitat of the native.”
In the end, “it seems a very fatuous argument to say if it’s vigorous, that’s better,” Suckling said.
Evaluation takes years
And in many cases, it takes years for the true effects of hybridization to be understood by scientists, said Susan Haig, a wildlife ecologist with U.S. Geological Survey and Oregon State University.
One example is the spotted owl, an animal she has studied. Native to the Pacific Northwest, the spotted owl’s population has declined since the early 1990s, as non-native barred owls have moved into the area — due at least in part to logging, experts believe.
The two species have hybridized, and “it’s a mixed bag,” Haig said.
“The hybrids seem to be OK … second- and third-generation babies grow up and seem fine — but it’s not helping spotted owls in any way, shape or form,” she said. “And what we’re finding is that the hybridization usually only happens for a couple of years, and then the barred owl kicks out the spotted owl.”
Another key consideration is the effect an emerging hybrid population has on other native species — a question Fitzpatrick said he and his colleagues plan to tackle.
But despite the disagreement over the implications for managing hybrid populations raised by the study, its critics said such forays into documenting species genetics are crucial to conservation decisions.
Suckling pointed to the recent discovery that Fish and Wildlife Service biologists working to restore the population of an endangered native trout species in Colorado were stocking rivers in the state with the wrong fish (Greenwire, Sept. 6).
“Why did that happen? Because no one was doing these genetic studies,” he said.