wes_von_papineäu
Our Roving Correspondent
SAN FRANCISCO CHRONICLE (California) 05 July 09 New threat emerges to tiger salamander (David Perlman)
As if it isn't enough that the California tiger salamander and other amphibian pond-dwellers are forced to fight for survival against overdevelopment and pollution in the state, along comes a predatory half-breed salamander to present another serious threat.
The trouble didn't come suddenly to the native tiger salamanders, those yellow-spotted creatures once abundant in the state's ponds and vernal pools.
Their problems began some 60 years ago - even before human development began seriously impinging on their habitats - when commercial bait sellers in California imported millions of alien Texas amphibians called barred tiger salamanders whose larvae, known as "waterdogs," made excellent bait for fishermen.
The adult barred salamanders, which look remarkably like their California cousins, soon began populating ponds all over Northern California. Harmless at first, Texas invaders quickly mated with the California natives and their hybridized descendants spread all over the state and have been flourishing ever since. They are imperiling frogs and newts and, above all, the original tiger salamander, according to a UC Davis biologist.
Maureen Ryan of the Center for Population Biology at UC Davis has published a report on the problem in the Proceedings of the National Academy of Sciences. It is the first complete scientific study ever made of the effects of this kind of hybridization on any animal.
Ryan and her colleagues sampled the habitats and studied the genetics of all three salamander species in ponds and pools throughout varied areas of California, particularly the Salinas Valley, where the salamanders are abundant and their problems striking. The team also built artificial ponds in the valley to study the natives and hybrids more closely.
More than 20 generations of hybridization, she and her colleagues reported, have resulted in a host of negative effects. One negative effect is that the hybrid salamanders out-compete the tiny larvae of the native tiger salamanders for food. With little food, the native larvae's normal transformation into full-grown adults becomes delayed, making the less agile little ones easy prey to the hybrids for a longer period of time each season, the researchers reported.
Ryan also reported changes in the genes of the hybrids. In a series of experiments conducted in artificial ponds on the Davis campus, she found that the hybrids are delaying emerging from their larval stage for longer and longer periods. She also noted that the hybrids have grown much larger than even the largest native tiger salamanders. Their gaping jaws, in fact, have become wide enough to engulf smaller varieties of the natives as well as their larvae, Ryan found.
Other victims of the hybrid hordes include Pacific Chorus frogs, otherwise known as California tree frogs, that are known for their raspy nocturnal trills, and the California newt that mostly occupies the moist forests of the state's coast range.
The hybridized salamanders also pose a threat to the survival of the rare and tiny endangered Santa Cruz long-toed salamander, whose only known habitat is a watery mating swamp near Watsonville. The habitat made news nearly 40 years ago when it was threatened by a proposed trailer park. It was finally ordered preserved only after UC and Cabrillo College students and scientists mobilized to save it.
In the report this week, Ryan also warned that the threatened California red-legged frog is in greater danger from the spread of the predatory hybrid salamanders. .
Because of heavily sprawling urban development, the California tiger salamanders have long been listed as threatened throughout the state, but small populations in Sonoma County and near Santa Barbara are designated as endangered, which calls for even greater habitat protection.
Even so, the hybrids pose a conundrum in some ways, Ryan said in an e-mail.
"The hybrids are displacing the native threatened species and are therefore a threat," she said. "But in places where they already exist, should we protect them because they're part native?"
The U.S. Fish and Wildlife Service, which can classify animals as threatened and endangered, is grappling with the issue, she said.
Ryan's co-authors are Jarrett Johnson, a colleague at UC Davis, and Benjamin Fitzpatrick, an evolutionary biologist at the University of Tennessee.
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2009/07/04/BANT18FQEJ.DTL&type=science
NATIONAL GEOGRAPHIC (Washington, DC) 29 June 09 Hybrid "Superpredator" Invading California Ponds (Christine Dell'Amore)
[Photo at URL below]: A "supersize" hybrid salamander is gulping down smaller amphibians—such as Pacific chorus frogs (F, the frog in its larval stage) and California newts (E, the newt in its larval stage)—in ponds throughout California's Salinas Valley, a June 2009 study found. The voracious hybrid (D, the largest variety, and C, the smallest) is a blend of the native California tiger salamander (A, the largest variety, and B, the smallest) and the invasive barred tiger salamander (not pictured). (Brian MacElvaine)
Mating between the rare California tiger salamander and the introduced barred tiger salamander has created a monster—at least for animals that dwell in the ponds of California's Salinas River Valley.
The new hybrid "superpredator" grows larger than either of its parent species, and its bigger mouth enables it to suck up a wide variety of amphibian prey, said lead study author Maureen Ryan, of the Center for Population Biology at the University of California, Davis.
Mostly on the menu are smaller pond species, such as the Pacific chorus frog and the California newt—both of which were "dramatically reduced" in population by the hybrid in the experiments.
This may be the case in natural ponds as well, Ryan said.
"[The hybrids] seem to be more voracious and a little more aggressive," Ryan said. "Just watching their behavior, they'll go after each other and the other prey."
To find out how the hybrid is impacting local ponds, Ryan collected tadpoles (juvenile frogs), larvae (juvenile salamanders) and eggs from various species from various sites within the valley and observed them in outdoor experimental ponds.
She and her team found that the hybrid larvae not only ate other amphibians, they also preyed on the native species' larvae.
Ryan's previous research has shown that the hybrid larvae even deploy an ambush strategy: When something swims by, the creatures attack and "jump and suck at the same time," she explained.
All aquatic salamanders are suction feeders, but the hybrids are more effective because of their large size, she added.
Other amphibian species are in danger if the hybrid's range continues to spread throughout the valley.
For instance, the Santa Cruz long-toed salamander, also listed as endangered in the U.S., lives in a very small range in Monterey County.
If hybrids moved into this area, they "could put a serious dent into the whole global population of the [long-toed] salamander," Ryan said.
Karen Lips, an amphibian biologist at the University of Maryland, College Park, said in an email that "the results of the paper show that the hybrids are having a significant impact on the other amphibians in these ponds."
And there are other examples in which salamanders have become top predators, added Lips, who was not involved in the research. In woodland ponds, for example, the amphibians dictate the populations of insects and other invertebrates.
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."
Research appears this week in the journal Proceedings of the National Academy of Sciences.
http://news.nationalgeographic.com/news/2009/06/090629-salamanders-hybrid.html
As if it isn't enough that the California tiger salamander and other amphibian pond-dwellers are forced to fight for survival against overdevelopment and pollution in the state, along comes a predatory half-breed salamander to present another serious threat.
The trouble didn't come suddenly to the native tiger salamanders, those yellow-spotted creatures once abundant in the state's ponds and vernal pools.
Their problems began some 60 years ago - even before human development began seriously impinging on their habitats - when commercial bait sellers in California imported millions of alien Texas amphibians called barred tiger salamanders whose larvae, known as "waterdogs," made excellent bait for fishermen.
The adult barred salamanders, which look remarkably like their California cousins, soon began populating ponds all over Northern California. Harmless at first, Texas invaders quickly mated with the California natives and their hybridized descendants spread all over the state and have been flourishing ever since. They are imperiling frogs and newts and, above all, the original tiger salamander, according to a UC Davis biologist.
Maureen Ryan of the Center for Population Biology at UC Davis has published a report on the problem in the Proceedings of the National Academy of Sciences. It is the first complete scientific study ever made of the effects of this kind of hybridization on any animal.
Ryan and her colleagues sampled the habitats and studied the genetics of all three salamander species in ponds and pools throughout varied areas of California, particularly the Salinas Valley, where the salamanders are abundant and their problems striking. The team also built artificial ponds in the valley to study the natives and hybrids more closely.
More than 20 generations of hybridization, she and her colleagues reported, have resulted in a host of negative effects. One negative effect is that the hybrid salamanders out-compete the tiny larvae of the native tiger salamanders for food. With little food, the native larvae's normal transformation into full-grown adults becomes delayed, making the less agile little ones easy prey to the hybrids for a longer period of time each season, the researchers reported.
Ryan also reported changes in the genes of the hybrids. In a series of experiments conducted in artificial ponds on the Davis campus, she found that the hybrids are delaying emerging from their larval stage for longer and longer periods. She also noted that the hybrids have grown much larger than even the largest native tiger salamanders. Their gaping jaws, in fact, have become wide enough to engulf smaller varieties of the natives as well as their larvae, Ryan found.
Other victims of the hybrid hordes include Pacific Chorus frogs, otherwise known as California tree frogs, that are known for their raspy nocturnal trills, and the California newt that mostly occupies the moist forests of the state's coast range.
The hybridized salamanders also pose a threat to the survival of the rare and tiny endangered Santa Cruz long-toed salamander, whose only known habitat is a watery mating swamp near Watsonville. The habitat made news nearly 40 years ago when it was threatened by a proposed trailer park. It was finally ordered preserved only after UC and Cabrillo College students and scientists mobilized to save it.
In the report this week, Ryan also warned that the threatened California red-legged frog is in greater danger from the spread of the predatory hybrid salamanders. .
Because of heavily sprawling urban development, the California tiger salamanders have long been listed as threatened throughout the state, but small populations in Sonoma County and near Santa Barbara are designated as endangered, which calls for even greater habitat protection.
Even so, the hybrids pose a conundrum in some ways, Ryan said in an e-mail.
"The hybrids are displacing the native threatened species and are therefore a threat," she said. "But in places where they already exist, should we protect them because they're part native?"
The U.S. Fish and Wildlife Service, which can classify animals as threatened and endangered, is grappling with the issue, she said.
Ryan's co-authors are Jarrett Johnson, a colleague at UC Davis, and Benjamin Fitzpatrick, an evolutionary biologist at the University of Tennessee.
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2009/07/04/BANT18FQEJ.DTL&type=science
NATIONAL GEOGRAPHIC (Washington, DC) 29 June 09 Hybrid "Superpredator" Invading California Ponds (Christine Dell'Amore)
[Photo at URL below]: A "supersize" hybrid salamander is gulping down smaller amphibians—such as Pacific chorus frogs (F, the frog in its larval stage) and California newts (E, the newt in its larval stage)—in ponds throughout California's Salinas Valley, a June 2009 study found. The voracious hybrid (D, the largest variety, and C, the smallest) is a blend of the native California tiger salamander (A, the largest variety, and B, the smallest) and the invasive barred tiger salamander (not pictured). (Brian MacElvaine)
Mating between the rare California tiger salamander and the introduced barred tiger salamander has created a monster—at least for animals that dwell in the ponds of California's Salinas River Valley.
The new hybrid "superpredator" grows larger than either of its parent species, and its bigger mouth enables it to suck up a wide variety of amphibian prey, said lead study author Maureen Ryan, of the Center for Population Biology at the University of California, Davis.
Mostly on the menu are smaller pond species, such as the Pacific chorus frog and the California newt—both of which were "dramatically reduced" in population by the hybrid in the experiments.
This may be the case in natural ponds as well, Ryan said.
"[The hybrids] seem to be more voracious and a little more aggressive," Ryan said. "Just watching their behavior, they'll go after each other and the other prey."
To find out how the hybrid is impacting local ponds, Ryan collected tadpoles (juvenile frogs), larvae (juvenile salamanders) and eggs from various species from various sites within the valley and observed them in outdoor experimental ponds.
She and her team found that the hybrid larvae not only ate other amphibians, they also preyed on the native species' larvae.
Ryan's previous research has shown that the hybrid larvae even deploy an ambush strategy: When something swims by, the creatures attack and "jump and suck at the same time," she explained.
All aquatic salamanders are suction feeders, but the hybrids are more effective because of their large size, she added.
Other amphibian species are in danger if the hybrid's range continues to spread throughout the valley.
For instance, the Santa Cruz long-toed salamander, also listed as endangered in the U.S., lives in a very small range in Monterey County.
If hybrids moved into this area, they "could put a serious dent into the whole global population of the [long-toed] salamander," Ryan said.
Karen Lips, an amphibian biologist at the University of Maryland, College Park, said in an email that "the results of the paper show that the hybrids are having a significant impact on the other amphibians in these ponds."
And there are other examples in which salamanders have become top predators, added Lips, who was not involved in the research. In woodland ponds, for example, the amphibians dictate the populations of insects and other invertebrates.
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."
Research appears this week in the journal Proceedings of the National Academy of Sciences.
http://news.nationalgeographic.com/news/2009/06/090629-salamanders-hybrid.html
