What’s the News: A fungus that his been wiping out frog species all over the world is creeping into the last area patch of tropical mountains in the Americas escape its scourge, the Darien National Park in Panama, and scientists are scrambling to save what species they can.
Frogs have been taking a beating over the last three decades, due in large part to a ruthless killer called chytrid fungus. Identified in the late ’90s, the fungus is startlingly lethal, driving 50% of species into extinction and killing 80% of individuals within five months of appearing at one location in Panama. It spreads through water via spores, affecting even areas where humans have not penetrated. “It is the worst infectious disease ever recorded among vertebrates in terms of the number of species impacted, and its propensity to drive them to extinction,” wrote a team of scientists in a 2005 World Conservation Union report [pdf].
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Yesterday marked a year since the devastating earthquake in Haiti, which killed at least 200,000 people and ruined much of Port-au-Prince. And while the human inhabitants of Haiti are still struggling back, there’s been a bit of good news from the wildlife sector. Biologists have rediscovered six frog species in the Haitian forest that haven’t been seen in two decades and were feared lost.
“I am very wary of highlighting frogs at this time in Haiti. Obviously the country has very pressing needs, but I think ultimately they are a symbol of something more hopeful,” said Robin Moore, an amphibian expert with Conservation International who helped lead the expedition that found the frogs. [MSNBC]
Moore’s expedition set out in search of the La Selle Grass frog (E. glanduliferoides), which hasn’t been seen since 1985 and is feared extinct; the mission was part of Conservation International’s “Search for Lost Frogs” campaign. The researchers didn’t find the La Selle Grass frog, but they found plenty of other frogs that they hadn’t expected to catch sight of.
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In August, Conservation International launched its globe-spanning search for amphibians that haven’t been seen in decades, but still could exist. This month, they’ve tracked down their first three slippery specimens. Scientists turned up two long-lost African frogs and a salamander from Mexico.
“It’s pretty extraordinary to think about just how long it has been since these animals were last seen,” observed project co-ordinator Robin Moore of Conservation International (CI). “The last time that the Mexican salamander was seen, Glenn Miller was one of the world’s biggest stars. The Omaniundu reed frog disappeared the year that Sony sold its first ever Walkman.” [BBC News]
The three rediscovered animals are:
The Mount Nimba reed frog (right). Last seen in 1967, it lives in the Ivory Coast. A local scientist spotted it.
The find was made “in a swampy field in Danipleu, an Ivorian village near the Liberia border.” [MSNBC]
Omaniundu Reed Frog (top). The most recently seen of the three, Omaniundu was last noted in 1979. It lives in the Democratic Republic of the Congo. According to Conservation International’s account of the rediscovery:
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Behold its minute majesty.
The micro frog’s moniker is Microhyla nepenthicola. It grows to just a half-inch long or less. It lives in pitcher plants, and it’s the smallest Old World frog species ever found. (The only smaller frog in the entire world is found in Cuba.)
Dr Indraneil Das of the Institute of Biodiversity and Environmental Conservation at the Universiti Malaysia Sarawak said the sub-species had originally been mis-identified in museums. “Scientists presumably thought they were juveniles of other species, but it turns out they are adults of this newly-discovered micro species,” he said [Reuters].
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Researchers have found the secret to improving a robot’s sense of smell: Shove frog eggs up its nose. A team at the University of Tokyo has developed a sensor made from a genetically modified frog egg that can help a robot pick out insect smells and pheromones.
As useful as a moth-smelling robot may seem, researchers believe the study published yesterday in Proceedings of the National Academy of Sciences is just one step towards an inexpensive but sensitive chemical detector. Study coauthor Shoji Takeuchi explains that such a device could pick out gases like carbon dioxide:
“When you think about the mosquito, it is able to find people because of carbon dioxide from the human. So the mosquito has CO2 receptors. When we can (extract) DNA (from the mosquito) we can put this DNA into the frog eggs to detect CO2.” [Reuters]
Here’s how they did it.
Step 1 — Get Some Frog Eggs
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In 18 countries around the world, biologists are setting out what may be fruitless quests. Conservation International is sponsoring expeditions to seek 40 amphibian species that haven’t been spotted for over a decade, and that may well be extinct. The group hopes its “Search for Lost Frogs” project will draw attention to the plight of amphibians, which are threatened by fungal diseases, toxic chemicals, habitat loss, and climate change–some researchers even say the global population decline is a sign that the world’s sixth mass extinction event is underway.
Dr Robin Moore, of Conservation International, a US-based charity, said: “This role as the global ‘canary in a coalmine’ means that the rapid and profound change to the global environment that has taken place over the last 50 years or so – in particular climate change and habitat loss – has had a devastating impact on these incredible creatures.” [The Guardian]
Still, the biologists hope they’ll find that some of these 40 species are still hanging on. “Although there is no guarantee of success,” Conservation International said in a press release, “scientists are optimistic about the prospect of at least one rediscovery.”
The group also compiled a list of the 10 “most wanted” species. Photo gallery after the jump.
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Atrazine, one of the world’s most widely used herbicides, is wreaking havoc on the sex lives of male frogs. In a new experiment, exposure to the chemical emasculated more than half of the male African claw frogs in the study, and made one in ten turn into females. The results, which were published in the Proceedings of the National Academy of Sciences, have raised concerns that the herbicide found in waterways is altering amphibians’ hormones, and could potentially have similar effects on other animals, including humans.
Biologist Tyrone Hayes studied 40 male control tadpoles along with 40 male tadpoles reared in water tainted with atrazine. The levels of the chemical matched the levels the frogs would encounter in their natural settings, and was also within the drinking water standards set by the Environmental Protection Agency. The results showed that 75 percent of male tadpoles reared in atrazine-contaminated water developed into frogs that had low testosterone levels, decreased breeding gland size, feminized laryngeal development, suppressed mating behavior, reduced sperm production and decreased fertility, while the control group showed features typically found in male frogs [AFP]. Most of these “chemically castrated” frogs were unable to reproduce.
The rest of the results were even more dramatic. Ten percent of tadpoles raised in the chemically tainted water developed into frogs with male genetics but female anatomy, and some of these were actually able to breed and produce eggs. The offspring, researchers found, were all male because both parents contributed male genes. Scientists worry that the sex-reversed males and the subsequent production of all-male offspring is skewing the sex ratio of wild frog populations, and may be contributing to the decline of frog populations worldwide.
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Monogamy isn’t popular in the amphibian world. From frogs to salamanders, life in cold blood is all about meeting new ladies and hitting the road once the kids are born. So the male of a species of Peruvian poison frog (Ranitomeya imitator) stands out by proving that he is quite the keeper. He’s not only the first monogamous frog ever found, he also stays home and makes sure the tadpoles are fed.
Scientists studying these frogs say this unusual behavior–monogamy and co-operative parenting–could be directly attributed to the limited resources available to the frogs. They note that a broad study of 404 frog species show that species that deal with reduced food availability and greater difficulty in tadpole-rearing are more likely to have frog couples that work together to raise the young.
These findings could possibly shed some light on the way our hunter-gatherer ancestors approached monogamy. Details of the findings are to be published in the April issue of The American Naturalist.
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Frog tadpoles have a good nose for danger: Scientists know that they go from headlong swimming to total stillness when they smell a predator. Now, researchers have discovered that frogs get that odoriferous training very early on. When they’re still embryos, they can learn to assess the threat level by sniffing for a predator’s pheromones.
Embryos put into water containing the odour of a salamander and the odour of injured tadpoles learned that the predator’s smell was a threat [BBC News]. The idea was to see if the amphibian embryos could learn to associate the smell of injured tadpoles with the smell of a predator. This type of learning behavior has also been observed in previous experiments with fish, larval amphibians, and larval mosquitoes, however this was the first study to document the behavior in embryos.
In an experiment sure to make PETA squirm, crushed tadpoles were mixed with water in which a tiger salamander had been swimming. Embryos were raised in this water with different concentrations of crushed tadpoles. Once the embryos had hatched into tadpoles, researchers tested their response to only the salamander odor. The tadpoles that were exposed to a higher concentration of the injured tadpole odour stayed motionless for longer in response to the salamander cue [BBC News]. The scientists say this demonstrates that these tadpoles learned as embryos that salamanders were more dangerous predators. The researchers published their findings in the journal Behavioural Ecology and Sociobiology.
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Image: Maud Ferrari, UC Davis
The chytrid skin fungus is killing frogs around the world, and researchers worry that it is already driving some species to extinction–but until now, no one understood how the fungus killed. Now, new research shows that the fungus disrupts the flow of nutrients through the frogs’ skin, ultimately leading to cardiac arrest.
In the study, which will be published tomorrow in Science, the scientists found that the fungus interferes with the frogs’ ability to absorb electrolytes, the electrically conducive molecules that are vital for muscle and nerve function. Diseased green tree frogs had dramatically lower levels of potassium and sodium in their blood and urine. Says study coautor Wyatt Voyles: “It’s a failure of the electrical system, leading to mechanical failure. If you don’t have a normal electrical system pacing the heart, it won’t pump blood” [Wired.com].
Further experiments confirmed that the electrolyte imbalance led to a heart shutdown. The scientists took electrocardiogram recordings of the frogs’ hearts in the hours before death; and found changes to the rhythm culminating in arrest. Drugs that restore electrolyte balance brought the animals a few hours or days of better health, some showing enough vigour to climb out of their bowls of water; but all died in the end [BBC News]. Researchers’ next task will be to determine exactly how the fungus interferes with the electrolyte absorption: it could be a result of cell damage in the skin, or a toxin produced by the fungus.
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Image: Jamie Voyles, Alex Hyatt, and Frank Fillipi
Pity the poor frogs: they’re one of the most endangered group of vertebrates on the planet, and new research shows that two of the factors in their plight are common, everyday farm chemicals. The study shows that atrazine, a weedkiller that’s widely used in agricultural areas, not only boosts the levels of parasitic flatworms in frog ponds, it also decreases tadpoles’ ability to fight off infections. If that wasn’t bad enough, previous research has found that runoff from phosphate fertilizers also boosts parasite levels. Taken together, researchers say, the weedkiller and the fertilizers are hitting frogs with a double whammy.
Amphibian populations around the world have been declining in recent decades, with many species on the brink of extinction. Infection with any of several species of tiny flatworms, known as trematodes, can trigger debilitating limb deformities in frogs. Severe infections can kill the amphibians. The question was why high rates of those deformities — and, presumably, trematode infections — began showing up across the nation in the mid-1990s [Science News]. The new findings suggest that the growing prevalence of the weedkiller atrazine in corn-growing regions since that time may be partly to blame for the woeful state of American amphibians.
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