 |
|
Genetic analysis finds greater threat in frog-killing fungus
August 07, 2007Berkeley -- A deadly fungus that has decimated populations of mountain yellow-legged frogs in the Sierra Nevada can likely be spread by sexual reproduction, seriously complicating efforts to save the frogs from extinction, according to a new genetic analysis led by researchers at the University of California, Berkeley.
The dramatic decline of the mountain yellow-legged frog over the past several decades has been attributed to the introduction of non-native predatory fish in some areas and to chytridiomycosis, a quickly spreading disease caused by this waterborne fungus, Batrachochytrium dendrobatidis.
The study, to appear in next week's edition of the journal Proceedings of the National Academy of Sciences, suggests that the frog-killing fungus may end up playing the bigger role in the frog's demise because of the pathogen's ability to spread over long distances and possibly persist in the environment as a consequence of sexual reproduction, according to the researchers.
"This group of fungi, when it reproduces sexually, can create spores that can last for a decade," said John Taylor, UC Berkeley professor of plant and microbial biology and principal investigator of the study. "That could make this pathogen a harder problem to defeat. As a resistant spore, the fungus could be transported by animals, including humans or birds, or lay dormant in an infected area until a new host comes along."
Biologists are still determining exactly how this fungus, first identified in 1998, kills the amphibians it infects, but most believe that the pathogen disrupts the frogs' ability to absorb water through its skin.
In the western United States, the fungus has been spreading quickly, moving west to east across the Sierra Nevada at a pace of about a mile per year, according to the researchers. Tens of thousands of mountain yellow-legged frogs in hundreds of sites have virtually disappeared in the wake of the pathogen's emergence in the area.
The researchers set out to determine which of two competing hypotheses for the origin of chytridiomycosis was more plausible. If the fungus was recently introduced to an area, the researchers would expect to find a single genotype that had spread by clonal reproduction. If, however, the fungus is endemic to a region, they would expect to find diverse genotypes resulting from a long history of association that provides enough time for isolates to diverge through mutation and genetic recombination.
If the fungus is endemic to a region, the animals in the area would normally be resistant to its destructive effects because they would have co-evolved together. However, biologists theorize that changes to the environment - from global warming to pollution from agricultural chemicals - could make native frog populations susceptible to a pathogen with which they've previously co-existed.
According to the study, neither epidemic spread nor endemism alone explains the decline of these frogs.
"We found sites dominated by a single fungal genotype, which suggests a recent spread of the pathogen through clonal reproduction," said lead author Jess Morgan, who was a UC Berkeley post-doctoral researcher working with Taylor at the time the study was conducted. "But this study also provides the first evidence of genetic recombination in B. dendrobatidis, which results in multiple, related genotypes and signals that sexual reproduction is occurring."
The findings could help explain the global spread of this pathogen, which has also been found in South America, Australia, Europe and Africa, said the researchers. While human-assisted spread is possible, the fungus has infected amphibians in pristine areas too remote for human activity.
"Up until now, people thought the movement of this pathogen was mainly via infected frogs, so such measures as restrictions on the pet trade were put in place," said Morgan, who is now a research scientist at the Department of Primary Industries and Fisheries in Queensland, Australia. "If, in fact, this fungus produces resistant spores, people could be unwittingly transferring this pathogen around the world from dirt on our shoes or car tires. But spores could also hitchhike on the feathers of birds for quick transport across mountain ranges."
Moreover, if resistant spores remain in lakes where previous populations of frogs have succumbed to chytridiomycosis, attempts to repopulate the lakes with healthy frogs will likely fail.
Study co-authors Roland Knapp, ecologist at UC Santa Barbara's Sierra Nevada Aquatic Research Laboratory, and Vance Vredenburg, a post-doctoral scholar in integrative biology at UC Berkeley, have led a number of such efforts to reintroduce mountain yellow-legged frogs in remote lakes in the Sequoia and Kings Canyon national parks and the John Muir Wilderness. The sites were areas where previous frog populations had been wiped out by chytridiomycosis.
Out of 10 reintroduction attempts over the past four years, seven have failed, the authors said.
"Within two years, the healthy frogs we introduced would become infected with the fungus and die," said Knapp. "It's a stunning thing to see. One year, there is no obvious evidence of the disease, the next year, we'd come back to see hundreds of dead or dying frogs, and then the following year, they'd all be gone."
Although genetic testing should be able to detect the spores, scientists do not know where to look for them. In addition, blindly testing environmental samples has thus far failed to yield evidence of the spores.
Infected frogs can be treated with fungicides to remove the pathogen, but researchers say it is not a practical long-term solution since they would remain susceptible to re-infection if returned to the same lake.
To conduct the study, researchers collected two species of mountain yellow-legged frogs from six sites in the Sierra Nevada. Rana sierrae is found in northern Sierra Nevada and represented in the study by frogs at the sites at Little Indian Valley, Summit Meadow and Mono Pass, while Rana muscosa is found in southern Sierra Nevada, where study sites Laurel Lake, Hitchcock Lakes and Woods Lake are located.
The sites at Mono Pass and Summit Meadow are both easily accessible to humans by Tioga Pass Road, a popular thoroughfare in Yosemite National Park. Accessing the other four sites, however, was decidedly more difficult, necessitating hikes of two to three days or, on several occasions, the use of helicopters.
The researchers cultured the fungi samples obtained from the 100 frogs collected and had the pathogen's genome sequenced by the U.S. Department of Energy's Joint Genome Institute in Walnut Creek, Calif. They compared genetic markers for the Sierra Nevada B. dendrobatidis samples with fungi collected from other regions around the world.
"The genotypes of our fungi in the Sierra are not that different from genotypes found around the world," said Taylor. "That means there must be someplace else on earth where this fungus is endemic. One would guess that the frogs living where the ancestral population of this fungus is located would not be affected that badly. We could then try to determine the mechanisms those frogs use to resist the pathogen."
The study also found that the sites near Tioga Pass Road contained two similar populations of fungi. Because the lakes are 40 kilometers apart, the evidence is strong that movement of the fungi between the two locations was somehow assisted by humans, said the researchers.
"If we confirm that spores are a factor, then there may be precautions we can take to contain their spread," said Morgan. "This could involve cleaning shoes before moving from one infected site to another. Some fungi produce spores during certain times of the year. If that is the case with this fungus, we could consider restricting public access to infected sites during those times."
As the U.S. Fish and Wildlife Service considers listing the mountain yellow-legged frog as an endangered species, biologists are racing to find ways to staunch the spread of the frog-killing fungus.
"This frog used to be the most abundant amphibian, and perhaps the most abundant vertebrate, in the whole Sierra Nevada," said Knapp. "Over the past 30 years, it has disappeared from up to 95 percent of its historic range, and its absence is impacting other organisms. Garter snakes that used to prey on these frogs are now declining. The frog's decline is leading to an unraveling of a high-elevation ecosystem."
University of California - Berkeley
"This group of fungi, when it reproduces sexually, can create spores that can last for a decade," said John Taylor, UC Berkeley professor of plant and microbial biology and principal investigator of the study. "That could make this pathogen a harder problem to defeat. As a resistant spore, the fungus could be transported by animals, including humans or birds, or lay dormant in an infected area until a new host comes along."
Biologists are still determining exactly how this fungus, first identified in 1998, kills the amphibians it infects, but most believe that the pathogen disrupts the frogs' ability to absorb water through its skin.
In the western United States, the fungus has been spreading quickly, moving west to east across the Sierra Nevada at a pace of about a mile per year, according to the researchers. Tens of thousands of mountain yellow-legged frogs in hundreds of sites have virtually disappeared in the wake of the pathogen's emergence in the area.
The researchers set out to determine which of two competing hypotheses for the origin of chytridiomycosis was more plausible. If the fungus was recently introduced to an area, the researchers would expect to find a single genotype that had spread by clonal reproduction. If, however, the fungus is endemic to a region, they would expect to find diverse genotypes resulting from a long history of association that provides enough time for isolates to diverge through mutation and genetic recombination.
If the fungus is endemic to a region, the animals in the area would normally be resistant to its destructive effects because they would have co-evolved together. However, biologists theorize that changes to the environment - from global warming to pollution from agricultural chemicals - could make native frog populations susceptible to a pathogen with which they've previously co-existed.
According to the study, neither epidemic spread nor endemism alone explains the decline of these frogs.
"We found sites dominated by a single fungal genotype, which suggests a recent spread of the pathogen through clonal reproduction," said lead author Jess Morgan, who was a UC Berkeley post-doctoral researcher working with Taylor at the time the study was conducted. "But this study also provides the first evidence of genetic recombination in B. dendrobatidis, which results in multiple, related genotypes and signals that sexual reproduction is occurring."
The findings could help explain the global spread of this pathogen, which has also been found in South America, Australia, Europe and Africa, said the researchers. While human-assisted spread is possible, the fungus has infected amphibians in pristine areas too remote for human activity.
"Up until now, people thought the movement of this pathogen was mainly via infected frogs, so such measures as restrictions on the pet trade were put in place," said Morgan, who is now a research scientist at the Department of Primary Industries and Fisheries in Queensland, Australia. "If, in fact, this fungus produces resistant spores, people could be unwittingly transferring this pathogen around the world from dirt on our shoes or car tires. But spores could also hitchhike on the feathers of birds for quick transport across mountain ranges."
Moreover, if resistant spores remain in lakes where previous populations of frogs have succumbed to chytridiomycosis, attempts to repopulate the lakes with healthy frogs will likely fail.
Study co-authors Roland Knapp, ecologist at UC Santa Barbara's Sierra Nevada Aquatic Research Laboratory, and Vance Vredenburg, a post-doctoral scholar in integrative biology at UC Berkeley, have led a number of such efforts to reintroduce mountain yellow-legged frogs in remote lakes in the Sequoia and Kings Canyon national parks and the John Muir Wilderness. The sites were areas where previous frog populations had been wiped out by chytridiomycosis.
Out of 10 reintroduction attempts over the past four years, seven have failed, the authors said.
"Within two years, the healthy frogs we introduced would become infected with the fungus and die," said Knapp. "It's a stunning thing to see. One year, there is no obvious evidence of the disease, the next year, we'd come back to see hundreds of dead or dying frogs, and then the following year, they'd all be gone."
Although genetic testing should be able to detect the spores, scientists do not know where to look for them. In addition, blindly testing environmental samples has thus far failed to yield evidence of the spores.
Infected frogs can be treated with fungicides to remove the pathogen, but researchers say it is not a practical long-term solution since they would remain susceptible to re-infection if returned to the same lake.
To conduct the study, researchers collected two species of mountain yellow-legged frogs from six sites in the Sierra Nevada. Rana sierrae is found in northern Sierra Nevada and represented in the study by frogs at the sites at Little Indian Valley, Summit Meadow and Mono Pass, while Rana muscosa is found in southern Sierra Nevada, where study sites Laurel Lake, Hitchcock Lakes and Woods Lake are located.
The sites at Mono Pass and Summit Meadow are both easily accessible to humans by Tioga Pass Road, a popular thoroughfare in Yosemite National Park. Accessing the other four sites, however, was decidedly more difficult, necessitating hikes of two to three days or, on several occasions, the use of helicopters.
The researchers cultured the fungi samples obtained from the 100 frogs collected and had the pathogen's genome sequenced by the U.S. Department of Energy's Joint Genome Institute in Walnut Creek, Calif. They compared genetic markers for the Sierra Nevada B. dendrobatidis samples with fungi collected from other regions around the world.
"The genotypes of our fungi in the Sierra are not that different from genotypes found around the world," said Taylor. "That means there must be someplace else on earth where this fungus is endemic. One would guess that the frogs living where the ancestral population of this fungus is located would not be affected that badly. We could then try to determine the mechanisms those frogs use to resist the pathogen."
The study also found that the sites near Tioga Pass Road contained two similar populations of fungi. Because the lakes are 40 kilometers apart, the evidence is strong that movement of the fungi between the two locations was somehow assisted by humans, said the researchers.
"If we confirm that spores are a factor, then there may be precautions we can take to contain their spread," said Morgan. "This could involve cleaning shoes before moving from one infected site to another. Some fungi produce spores during certain times of the year. If that is the case with this fungus, we could consider restricting public access to infected sites during those times."
As the U.S. Fish and Wildlife Service considers listing the mountain yellow-legged frog as an endangered species, biologists are racing to find ways to staunch the spread of the frog-killing fungus.
"This frog used to be the most abundant amphibian, and perhaps the most abundant vertebrate, in the whole Sierra Nevada," said Knapp. "Over the past 30 years, it has disappeared from up to 95 percent of its historic range, and its absence is impacting other organisms. Garter snakes that used to prey on these frogs are now declining. The frog's decline is leading to an unraveling of a high-elevation ecosystem."
University of California - Berkeley
Frog News and Current Frog Events RSSDying frogs sign of a biodiversity crisis
Devastating declines of amphibian species around the world are a sign of a biodiversity disaster larger than just frogs, salamanders and their ilk, according to researchers from the University of California, Berkeley.
Metabolic insight to illuminate causes of iron imbalance
New insight into key players in iron metabolism has yielded a novel tool for distinguishing among root causes of iron overload or deficiency in humans, the researchers report in the August issue of Cell Metabolism, a publication of Cell Press. While the body needs iron to produce hemoglobin, a substance in red blood cells that enables them to carry oxygen, too much iron can build up and eventually damage organs.
World's smallest snake found in Barbados
The world's smallest species of snake, with adults averaging just under four inches in length, has been identified on the Caribbean island of Barbados. The species -- which is as thin as a spaghetti noodle and small enough to rest comfortably on a U.S. quarter --was discovered by Blair Hedges, an evolutionary biologist at Penn State.
Researchers catch ion channels in their opening act
Each thought or action sends a million electrical signals pulsing through your body. At the heart of the process of generating these electrical impulses is the ion channel.
Weizmann Institute scientists discover how an injured embryo can regenerate itself
More than 80 years have passed since the German scientist Hans Spemann conducted his famous experiment that laid the foundations for the field of embryonic development.
When threatened, a few African frogs can morph toes into claws
Biologists at Harvard University have determined that some African frogs carry concealed weapons: When threatened, these species puncture their own skin with sharp bones in their toes, using the bones as claws capable of wounding predators.
New study reveals large scale conservation essential
Scientists were surprised with findings of a recent study that reveals many animal species believed to persist in small contained areas actually need broad, landscape level conservation to survive.
Probiotic bacteria protect endangered frogs from lethal skin disease
Laboratory tests and field studies conducted by James Madison University (JMU) researchers continue to show promise that probiotic bacteria can be used to help amphibian populations, including the endangered yellow-legged frog, fend off lethal skin diseases.
A missing link settles debate over the origin of frogs and salamanders
The description of an ancient amphibian that millions of years ago swam in quiet pools and caught mayflies on the surrounding land in Texas has set to rest one of the greatest current controversies in vertebrate evolution. The discovery was made by a research team led by scientists at the University of Calgary.
Female concave-eared frogs draw mates with ultrasonic calls
Most female frogs don't call; most lack or have only rudimentary vocal cords. A typical female selects a mate from a chorus of males and then -silently - signals her beau.
More Frog News Articles
 | Nursing Research: Generating and Assessing Evidence for Nursing Practice (Nursing Research (Polit)) by Denise F Polit, Cheryl Tatano Beck Thoroughly revised to emphasize the link between research and evidence-based practice, this Eighth Edition presents methods and tools for generating and assessing evidence for nursing practice. This edition offers more guidance on evaluating and critiquing research evidence. Other revisions include more in-depth coverage of both qualitative and quantitative research and a new chapter on... |
 | In Cold Blood by Truman Capote "Until one morning in mid-November of 1959, few Americans--in fact, few Kansans--had ever heard of Holcomb. Like the waters of the river, like the motorists on the highway, and like the yellow trains streaking down the Santa Fe tracks, drama, in the shape of exceptional happenings, had never stopped there." If all Truman Capote did was invent a new genre--journalism written with the language and... |
 | Careless in Red: A Novel by Elizabeth George In her most eagerly anticipated novel yet, Elizabeth George brings back Scotland Yard's Thomas Lynley to investigate a ruthless crime. After the senseless murder of his wife, Detective Superintendent Thomas Lynley retreated to Cornwall, where he has spent six solitary weeks hiking the bleak and rugged coastline. But no matter how far he walks, no matter how exhausting his days, the painful... |
 | The New Encyclopedia of Modern Bodybuilding : The Bible of Bodybuilding, Fully Updated and Revised by Arnold Schwarzenegger Arnold Schwarzenegger hasn't competed as a bodybuilder since he won the Mr. Olympia title in 1980, but he remains the sport's No. 1 icon. He hosts an annual bodybuilding contest in Columbus, Ohio, and allows a column to be ghost-written under his name in a muscle magazine. Today's bodybuilders may have bigger muscles than Arnold ever did, but everyone inside and outside the iron game gives him... |
 | On Chesil Beach by Ian Mcewan Such is Ian McEwan's genius that, despite rambling nature walks and the naming of birds, his subject matter remains hermetically sealed in the hearts of two people. It is 1962 when Edward and Florence, 23 and 22 respectively, marry and repair to a hotel on the Dorset coast for their honeymoon. They are both virgins, both apprehensive about what's next and in Florence's case, utterly and... |
 | Salem Falls by Jodi Picoult Love can redeem a man...but secrets and lies can condemn him.A handsome stranger comes to the sleepy New England town of Salem Falls in hopes of burying his past: Once a teacher at a girls' prep school, Jack St. Bride was destroyed when a student's crush sparked a powder keg of accusation. Now, washing dishes for Addie Peabody at the Do-Or-Diner, he slips quietly into his new routine, and Addie... |
 | Eat That Frog!: 21 Great Ways to Stop Procrastinating and Get More Done in Less Time by Brian Tracy The legendary Eat That Frog! (more than 450,000 copies sold and translated into 23 languages) provides the 21 most effective methods for conquering procrastination and accomplishing more. This new edition is revised and updated throughout, and includes brand new information on how to keep technology from dominating our... |
 | Principles of Marketing (Principles of Marketing) by Philip Kotler, Gary Armstrong The 11th edition of this popular text continues to build on four major marketing themes: building and managing profitable customer relationships, building and managing strong brands to create brand equity, harnessing new marketing technologies in the digital age, and marketing in a socially responsible way around the globe. Thoroughly updated and streamlined, Principles of Marketing tells the... |
 | The Da Vinci Code by Dan Brown The Da Vinci... |
 | Winter Study (Anna Pigeon Mysteries) by Nevada Barr Anna Pigeon returns—in the remarkable new novel from the New York Times–bestselling writer. It is January, and Park Ranger Anna Pigeon is sent to Isle Royale in Lake Superior to learn about managing and understanding wolves, as her home base of Rocky Mountain National Park might soon have their own pack of the magnificent, much-maligned animals. She’s housed in the island’s bunkhouse with the... |
| © 2008 BrightSurf.com |