“Superpredator” Hybrid Appears in California

8 July 2009 by Anne-Marie Hodge, posted in Uncategorized

The Salinas River Valley is apparently being terrorized by a new salamander “superpredator,” resulting from interbreeding between the California tiger salamander (Ambystoma californiense_) and an introduced species, the barred tiger salamander (Ambystoma tigrinum mavortium_). According to a fascinating new study conducted by a group of researchers from the Center for Population Biology at UC Davis and the University of Tennessee at Knoxville, the hybrid offspring grow much larger than either parent, with massive mouths that allow them to consume a much wider variety of amphibian prey, including rare frogs and salamanders such as the Santa Cruz long-toed salamander (Ambystoma macrodactylum croceum.)

Apparently the hybrids will not only consume other amphibians, they will also eat larvae of native species, a behavior not seen in their parents’ foraging patterns.

Even when the hybrids are tadpoles themselves, their predatory adaptations are the stuff of horror movies: some of them develop extra rows of teeth so they can cannibalize one another, a phenomenon also absent from the parent species.

Definitely makes for an interesting case study in hybrid vigor (aka heterosis or outbreeding enhancement. This is also bit of a conservation quandary, because although the hyper predatory behavior of these salamanders is threatening native species, they are also carrying on the genes of the endangered A. t. mavortium. The outlook for genetically pure populations of this species is grim, and this new bully species could be the only way to carry on the genes. The National Geographic report on the study includes this commentary from the study leader:

“Getting rid of the hybrid poses “ethical quandaries,” study leader Ryan said.
“From a conservation perspective, there [are] a lot of deep questions about what to do with this,” she said.
After all, the hybrid is part endangered species, so “do we protect [them] because they’re part native?”
Overall, Ryan said, her “real concern” is for the survival of California’s native salamander, which has shown to be no match for the half-Texan interloper.
The hybrid’s more aggressive predation “benefits the hybrid and harms the native, speeding up the process of converting populations into more hybrids.”

Personally, I don’t think that preserving the genes in this hybrid really counts as preserving the species, especially if it puts a multitude of other species at risk. Remember that if it were not for human introduction of the barred salamander, these hybridizations would not have occurred, so it cannot be considered “natural” in a broad sense. I have always viewed “species” as a label including not only genetics, but behavior and ecological role as well. This is why I am not a fan of zoos as primary conservation tools for large mammals (although I acknowledge their utility for public education). Take away ecological context, and you might have similar DNA, but the species itself is still lost.

So, what say you, is allowing this new hybrid to persist a responsible conservation strategy, or a conservation nightmare?

Ryan, M., J. Johnson, and B. Fitzpatrick. 2009. Invasive hybrid tiger salamander genotypes impact native amphibians. PNAS doi:10.1073/pnas.0902252106

(Credit for image of California tiger salamander)

One Response to ““Superpredator” Hybrid Appears in California”

  1. Travis Knowles Reply | Permalink

    I’m with you Anne-Marie. Wring those little hybrid necks . . .

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