The herptile blog.

All about the herpetological world.

Archive for the ‘Science/Scientific papers’ Category

All kind of scientific papers.

Morse Toad: When amphibians tap their toes

Posted by Miqe on November 7, 2008

Toe wiggling creates motions, vibrations that get potential prey moving.

Fowlers toads vibrate their hind toes when food shows up. Frogs and toads in at least seven families waggle their toes, though researchers are still figuring out whats going on. J. Sloggett

Fowler's toads vibrate their hind toes when food shows up. Frogs and toads in at least seven families waggle their toes, though researchers are still figuring out what's going on. J. SloggettWhen some toad toes tap, maybe it’s the beat, not the motion, that matters.The resulting vibrations could agitate insects and other little morsels, setting them wriggling and scuttling in a flurry of activity that triggers a toad’s known tendency to strike at moving prey, says entomologist John Sloggett of Groningen, the Netherlands.Details of how a toad’s brain processes information about when and where to strike will require deep amphibian neuroscience. But Sloggett and Groningen ecologist Ilja Zeilstra propose that vibration deserves attention in the study of what’s up with all the toe wiggling among frogs and toads.An adult Cane toad wiggles it´s hind toes when little toads show up, am intriguing motion that draws bite-sized juveniles close enough to be a cannibal´s lunch. Video shown in real time, then slowed down.

That study of toe motion surged in 2008, with two papers: a study in January’s Animal Behaviour on cane toads’ habit of “pedal luring,” and a paper by Sloggett and Zeilstra in the online version of the November Animal Behaviour.

Cane toads flutter their toes when small prey appear, and the intriguing pedal lure draws little cane toads closer to bigger cannibalistic ones, reported Mattias Hagman, now at Stockholm University in Sweden, and Rick Shine of the University of Sydney in Australia, in January.

Hagman and Shine studied a colony of captive cane toads for research on how to minimize damage to Australia’s native landscape as these big, poisonous toads invade. Hagman noticed that the arrival of crickets or a nearby aquarium full of bite-sized juveniles set the long middle toes of the adults’ hind feet waving.

A Mozambique rain frog waggles its feet when offered a mealworm, and the sound recording (from both toes) indicates that the motion taps out strong vibrations, which could play a role in nabbing prey.Sloggett & Zeilstra. 2008 Animal Behaviour

A Mozambique rain frog waggles its feet when offered a mealworm, and the sound recording (from both toes) indicates that the motion taps out strong vibrations, which could play a role in nabbing prey.Sloggett & Zeilstra. 2008 Animal Behaviour

To test the effects of toe waving, Hagman and Shine built a mechanical toe that could wiggle at various rates and affixed it to a taxidermy mount of a deceased toad. Waving the toe didn’t much interest the crickets. But the motion did entice clusters of the juvenile toads to move closer to the stuffed mount, Hagman and Shine reported.

Older cane toads near water could easily encounter youngsters clustering there during the dry season, Shine says. Dissecting more than two dozen adults from the wild, Hagman and Shine found that 64 percent of the adults’ meals had been even smaller toads of their own species.

“By understanding these interactions, we might be able to work out ways to turn cannibalism to our advantage,” Shine says.

Waving toes to create an alluring motion makes sense with visually responsive prey, says Sloggett. But for frogs and toads eating mainly invertebrates, which don’t respond much to gestures, maybe it’s the vibrations and subsequent frenzy of motion that matter, he and ecologist Zeilstra suggest in their new paper.

The two researchers keep frogs and toads as a matter of personal interest, and Sloggett even brought North American amphibians with him to Europe after he recently finished a project at the University of Kentucky in Lexington. Observation of some of those companions brings the total number documented to at least 13 species across seven frog and toad families, the team reports.

Getting information about an animal’s diet in the wild isn’t perfect, but several species are known to eat a lot of invertebrates. One such toe-wiggler, the Mozambique rain frog, Breviceps mossambicus, probably doesn’t prey on vertebrates because it has such a small mouth. This frog flexes its long middle toe when it catches sight of food, and by feeding a rain frog on a sheet of plastic, the researchers recorded strong vibrations from the toe tapping.

Toe flexing for useful vibrations “sounds plausible to me,” Shine says. “But the data are yet to be gathered.” And vibrations and motion can work together, Hagman says.

From Science News

Posted in Amphibians, Herpetology, Herps in the news, International articles and news., Science/Scientific papers | 2 Comments »

Amphibians’ Ability To Predict Changes In Biodiversity Confirmed By New Study

Posted by Miqe on November 5, 2008

Biologists have long suspected that amphibians, whose moist permeable skins make them susceptible to slight changes in the environment, might be good bellwethers for impending alterations in biodiversity during rapid climate change.

Now two University of California biologists have verified the predictive power of this sensitive group of animals in a global study of species turnover among amphibians and birds. The study appears this week in the advance online version of the journal Proceedings of the National Academy of Sciences.

“Our study supports the role of amphibians as ‘canaries in the coal mine’,” said Lauren Buckley, a postdoctoral fellow at UC Santa Barbara’s National Center for Ecological Analysis and Synthesis and the first author of the study. “Amphibians are likely to be the first to respond to environmental changes and their responses can forecast how other species will respond.”

“Amphibians are much more tuned in to the changes in their specific environments,” said Walter Jetz, an associate professor of biology at UC San Diego and the other author of the study. “They are much more sensitive to differences in environmental conditions as you move geographically from one location to another.”

The two scientists used maps of the environment and amphibian and bird distributions to answer the question of how the environment—as well as the distribution of birds and amphibians—changes as one moves from one place to another around the globe.

The researchers found that if the environment changes rapidly as one travels from one location to another, the amphibian and bird communities also change rapidly.  However, the species of amphibians would change more quickly than species of birds.  This confirms that amphibians are particularly sensitive to changes in the environment, the researchers conclude, and that this sensitivity is particularly acute given their narrow distributions.

Whether one is traveling through a tropical or temperature region also influences how quickly the types of animals change.  Given a mountain of a certain size, the researchers found, the amphibian and bird communities change more quickly if one is climbing a mountain in the tropics than in a temperate region.

“There are more species in the tropics and the species are generally more specially adapted to particular environmental conditions,” said Jetz. “This suggests that tropical species may be more severely impacted by a given temperature increase as a result of climate change.”

For the study, he and Buckley produced a series of global maps of environmental turnover and the associated changes in amphibian and bird communities that reveal that the identities of birds and amphibians change particularly quickly in mountainous regions such as the Andes and Himalayas.

“Understanding how environmental changes over space influence biodiversity patterns provides important background for forecasting how biodiversity will respond to environmental changes over time such as ongoing temperature increases,” said Buckley.

The study was supported by grants from the National Science Foundation, UC Santa Barbara and the State of California.
Adapted from materials provided by University of California – San Diego.

From Herpdigest.org

Posted in Amphibians, Herpetology, Herps in the news, International articles and news., Science/Scientific papers | 1 Comment »

Popular agrochemical linked to frog disease

Posted by Miqe on November 4, 2008

Atrazine, one of the world’s most widely-used herbicides, makes frogs more susceptible to disease by compromising their immune system, US scientists suggest. The study provides further evidence linking the herbicide to a global decline in amphibian populations over the last three decades.

‘Amphibians are perhaps the most threatened vertebrates on the globe,’ says Jason Rohr, who led the work at the University of South Florida. Since the 1980s, he explains, amphibian populations have been declining at a startling rate. 

Local chemical pollution has been blamed along with global climate change. But links between pollution and amphibian diseases are not clear, says Rohr.

Rohr and colleagues studied parasitic infection of the leopard frog (Rana pipiens) – a declining species – in wetlands across Minnesota. Of 240 possible factors, the researchers found that atrazine and phosphate, a common component of fertiliser, were the best predictors of the abundance of parasitic flatworm infection in the frogs – which can lead to malformed limbs, kidney damage, and death.

The leopard frog, a species in decline

The leopard frog, a species in decline

Back in the laboratory, the team found that frogs of various species exposed to atrazine were more likely to have a suppressed immune system, judging by measurements of immune cells. Atrazine also appeared to increase concentrations of the snails that harbour flatworm parasites. 

Banning chances

Atrazine has already been suspected of causing a variety of ill-effects in frogs, such as growth defects and reduced sex hormone production. The chemical was banned on fears of groundwater contamination by the European Union in 2004. But it is still commonly used in the US; in 2006, the country’s Environmental Protection Agency concluded there was not enough evidence to suggest the chemical was harmful to humans.

‘I doubt that further documentation of atrazine’s harmful effects on frogs will prompt a ban in the US anytime soon,’ says Pieter Johnson, an expert on amphibians at the University of Colorado at Boulder, US.  

‘In some respects amphibian development mirrors human development very closely and could therefore be used as a bioindicator. But in other regards, amphibians and humans are very different both ecologically and physiologically,’ Johnson adds. ‘Work such as this, in combination with more findings that atrazine could pose a threat to humans may push towards a ban in the US.’ 

A falling population of amphibians is itself a cause for concern, let alone any effect on humans, notes Rohr. Though bullfrogs and cane toads have been castigated for being invasive predators, most native amphibians are important for controlling insect pests that attack crops, and, as prey for birds and mammals, provide a link between freshwater and terrestrial ecosystems. 

Lewis Brindley

From RSC Cemistry World

Posted in Amphibians, Herpetology, Herps in the news, International articles and news., Science/Scientific papers | 2 Comments »

7 new species of frog discovered in Ecuador

Posted by Miqe on October 24, 2008

Hyalinobatrachium ruedai (© Diego F. Cisneros-Heredia); Centrolene durrellorum (© Mario Yánez-Muñoz); Nymphargus cochranae (© Roy McDiarmid); and Centrolene Mariaelenae (© Jesse Delia).

Seven previously unknown species of frog discovered over the past two years by Ecuadorian researchers are already under threat from habitat loss, reports a newsletter from the IUCN Amphibian Specialist Group.

The frogs belong to the Glassfrog family, a group that is endemic to tropical America and has more than 140 species, of which 40 percent are threatened with extinction due to disease and habitat loss.

Of the newly described species, six were found in eastern Ecuador, one of the most biodiverse, but least studied, parts of the country. Research suggests that deforestation may already been impacting these species.

Interested in the rest of this article? Please visit Mongabay.com

Posted in Amphibians, Fieldherping, Herpetology, Herps in the news, International articles and news., Science/Scientific papers | Leave a Comment »

Armageddon for amphibians? Frog-killing disease jumps Panama Canal

Posted by Miqe on October 13, 2008

Chytridiomycosis — a fungal disease that is wiping out amphibians around the world — has jumped across the Panama Canal, report scientists writing in the journal EcoHealth. The news is a worrying development for Panama’s rich biodiversity of amphibians east of the canal.

Chytridiomycosis is caused by Batrachochytrium dendrobatidis, a fungal pathogen that has been implicated in the extinction of more than 100 species of frogs and toads since the early 1980s. While scientists don’t yet know the origin of the fungus, they suspect it might be the African clawed frog, a species that has been shipped around the world for research purposes. The fungus is highly transmissible and has spread to at least four continents, in some cases probably introduced unintentionally by humans in the treads of their shoes. As it spreads, the disease lays waste to more than 80 percent of amphibians across a wide range of habitats, including those that are undisturbed by humans. Some researchers have suggested that climate change could be creating conditions that exacerbate the impact of the pathogen — which predominantly affects highland species — although the theory is still controversial.

Panama golden frogs mating in captivity. Photo by Rhett A. Butler

Panama golden frogs mating in captivity. Photo by Rhett A. Butler

“Our results suggest that Panama’s diverse and not fully described amphibian communities east of the canal are at risk,” the authors write. “Precise predictions of future disease emergence events are not possible until factors underlying disease emergence, such as dispersal, are understood. However, if the fungal pathogen spreads in a pattern consistent with previous disease events in Panama, then detection of Bd at Tortí and other areas east of the Panama Canal is imminent.”

Full article at Mongabay.com

Posted in Amphibians, Herpetology, Herps in the news, International articles and news., Science/Scientific papers | Leave a Comment »

Ultrasonic frogs can tune their ears to different frequencies

Posted by Miqe on July 28, 2008

Researchers have discovered that a frog that lives near noisy springs in central China can tune its ears to different sound frequencies, much like the tuner on a radio can shift from one frequency to another. It is the only known example of an animal that can actively select what frequencies it hears, the researchers say.

The findings, from a collaborative effort led by the University of Illinois and the University of California at Los Angeles, appear this week in Proceedings of the National Academy of Sciences. The research team also included scientists from the Chinese Academy of Sciences and the Massachusetts Eye and Ear Infirmary (at Harvard Medical School).

The discovery was made when researchers examined the eardrums of an unusual frog, Odorrana tormota, which communicates by making birdlike calls in the audible and ultrasonic frequency ranges. Previous research by two of the authors showed that the frog produces and responds to ultrasonic calls. In the new study they sought to determine whether the frog’s eardrums actually vibrate in response to these ultra high frequency sounds.

Using a laser vibrometer to measure the eardrum’s vibration, the researchers found that the eardrum did respond to sounds in the sonic and ultrasonic ranges. But they also saw something they couldn’t explain: The eardrum’s sensitivity to ultrasound sometimes disappeared altogether.

Normally sound waves strike the eardrum and – if they are powerful enough and in a frequency range that the animal can perceive – cause the eardrum to vibrate. In most studies of frogs, the eardrum responds exactly the same way to the same sound stimulus. Even the eardrums of a dead frog will respond with unchanging predictability.

Past research showed that a frog’s eardrum never responds differently to the same sound stimulus, said team leader Albert Feng, a professor of molecular and integrative physiology at Illinois.

“This was contrary to everything that we knew about its auditory system,” he said.

O. tormota, the concave-eared torrent frog, is unusual in other ways. Most frogs have ears on the body surface, but the torrent frog’s ears are recessed. Feng and his colleagues previously reported that O. tormota communicates in a noisy environment by emitting high frequency calls that include ultrasonic sounds, and can localize sound with astonishing precision. Upon hearing a female call, a male will leap directly toward the sound with an error of less than 1 percent, a feat previously unheard of in frogs.

Fortunately for the researchers, the eardrum of O. tormota is transparent, offering a view of its inner workings in a living frog.

While puzzling over the peculiar results of the eardrum vibration measurements, the researchers noticed the sudden appearance and disappearance of a dark shadow on the eardrum, Feng said.

Further investigation revealed that the frogs were actively opening and closing their Eustachian tubes, the two narrow channels that connect either side of the pharynx to the left and right middle ear. The changing state of the Eustachian tubes was more readily observed by directing a light beam at the mouth from under the frog’s chin. When the Eustachian tubes were open, the light was visible through the eardrum. When they closed, the circles of light glowing out through the ears disappeared. (Movie available.)

“We said, ‘Whoa! This is bizarre!’ ” Feng recalled. “In all textbooks on sound communication and hearing in frogs, it is plainly stated that the Eustachian tubes are permanently open!”

Feng and his colleagues had observed that when open, the Eustachian tubes essentially couple the frog’s left and right ears. This “acoustic coupling” between the ears makes them sensitive to sound direction, enabling the frog to localize sound, Feng said.

To determine the consequence of active closure of the Eustachian tubes, the researchers measured how the open and closed Eustachian tubes affected the vibration of the eardrum.

They found that the frogs’ eardrums became very sensitive to high frequency and ultrasounds when their Eustachian tubes were closed, compared with when they were open. When the Eustachian tubes were open, the eardrums responded mostly to low frequency sounds.

The frogs appear to be able to tune in to specific sound frequencies at will, Feng said. They can shift to high frequency and ultrasonic hearing when the low frequency background noise of rushing water is too intense for them to pick out the calls of potential mates or rivals, he said.

This research likely has implications for human health. Earlier research into the mechanics of frog hearing helped Feng and his colleagues at the U. of I.’s Beckman Institute for Advanced Science and Technology design an “intelligent hearing aid” that boosts sound signals of interest.

From Innovations Report

Posted in Amphibians, Herps in the news, International articles and news., Science/Scientific papers | Leave a Comment »

Human-frog hybrids reveal autism’s secrets

Posted by Miqe on July 28, 2008

Human-frog hybrids might reveal the neurological secrets of autism. By fusing cells from the preserved brains of deceased autistic patients with the eggs of a carnivorous African frog called Xenopus, scientists have started investigating the way the brain cells of people with autism behave.

The frog eggs work a little like human neurons and the hybrid cells act as a surrogate of a living brain with the condition.

“It’s almost as if you were studying a neuron in the human brain,” says Ricardo Miledi, a neurobiologist at the University of California, Irvine, who developed the approach and has previously used Xenopus eggs to study epilepsy.

Miledi’s earlier work has suggested that some brain cells of epilepsy patients have trouble sensing a molecule that helps damp down neuron activity. The proteins in question, called neurotransmitter receptors, sense the chemicals that neurons use to communicate, and Miledi thinks that problems with these proteins underlie epilepsy and other disorders

Some researchers blame autism on a malfunction in mirror neurons, cells that play a vital role in understanding the actions of others people.

To see if abnormalities in neurotransmitter signalling also underlie autism, Miledi’s team collected brain samples from six deceased autistic patients, aged eight to 39. They fused brain-cell membranes, which house neurotransmitter receptors, together with Xenopus egg membranes. As a control, they did the same thing with brain cells from patients with no history of mental disorder.

Miledi’s team then doused the frog eggs in neurotransmitter chemicals, and measured the voltage generated within each egg. The neurotransmitter chemicals tell brain cells to pump charged molecules in and out the membrane, creating a voltage across the membrane. Since Xenopus eggs do not respond to the neurotransmitters, the human proteins are completely responsible for any electric current generated.

Four of six autistic brains responded to neurotransmitters chemicals less vigorously than the controls.

However, Miledi cautions that more research with additional samples will be needed to firm up any conclusions. “Autism spectrum disorder is a very broad range of maladies, with many different sources and many different problems,” he says.

Jonathan Pevsner, a neurobiologist at Kennedy-Krieger Institute in Baltimore, Maryland, agrees that frog eggs could be useful for studying certain properties of autism, and perhaps uncovering new treatments.

He notes that other brain illnesses, such as depression and Parkinson’s, can be treated by turning the activity of neurotransmitters up or down. Hybrid frog eggs could perhaps hint at which neurotransmitters to tweak, he says.

Journal reference: PNAS (DOI: 10.1073/pnas.0804386105)

From New Scientist

Posted in Amphibians, Herps in the news, International articles and news., Science/Scientific papers | Leave a Comment »

An amphibious assault

Posted by Miqe on June 16, 2008

LONDON

– The first images that come to mind may be unassuming brown newts or garden-variety green frogs, but amphibians cover a much grander spectrum.

Among about 6,000 species of frogs, salamanders and caecilians (legless animals, pronounced like “Sicilians”) are some of the world’s most bizarre animals: Giant Chinese salamanders, two metres in length; the “hairy frog” of Cameroon, which not only looks like it sports hair, but also can break its own bones to grow claws (an ability discovered just last month); the Surinam toad, which carries its eggs embedded in its back; and, even more macabre, the Sagalla caecilian, which feeds its own skin to its young.

Amphibians are also among the most colourful animals: The tiny, bright-yellow poison frog (with the spectacular scientific name Phyllobates terriblis) from Colombia, which is, gram for gram, the most poisonous vertebrate in the world; the black-dotted yellow frogs of Panama, which communicate with adorable hand waves; and the charismatic red-eyed tree frogs, aptly nicknamed “swimsuit calendar frogs.”

These make up just a small sample of the amazingly diverse amphibians, which have the longest history on earth. They predate all other terrestrial vertebrates.

But the first group of animals to colonize the land is also the first that humans are driving off it. Amphibians are disappearing faster than any other animals since the dinosaurs: 32 per cent of all species are threatened with extinction, compared with 23 per cent of mammals and 12 per cent of birds. Almost half are in decline.

The reasons are complex and vary among species. Some are hunted for the pet trade or, as with the Chinese salamander, for their meat. The destruction of habitat, as with all animals, is a major cause worldwide. Pollution also appears to be a big factor.

But one of the most worrisome and headline-grabbing causes is a strange fungus: Batrachochytrium dendrobatidis, a.k.a. chytrid. Nobody quite knows how it kills amphibians – it may smother them, covering the skin they use to absorb oxygen and water, or it might release toxins. But biologists are unanimous in their belief that it is wiping out amphibians across the tropics, in the warm and wet conditions in which they thrive, from Australia to South America. Scientists believe that it is behind the disappearance of 74 species (out of an original 110) of harlequin frog in Central America and at least 10 species of Australian frogs.

Bob Johnson, curator of reptiles and amphibians at the Toronto Zoo, saw one of the fungus’s first victims just before it vanished. The golden toad of Costa Rica was once so numerous that tourists would flock to witness their mating season. They were so dense on the forest floor, “we could barely walk, there were so many of them,” Mr. Johnson says of a trip he made in 1987. Just two years later, they had all disappeared, driven into extinction. “It was just astonishing.”

Now, Mr. Johnson is caring for one of the last populations of Panama golden frogs, the stars of the most recent David Attenborough BBC documentary, Life in Cold Blood. The frogs were all taken out of the wild before chytrid reached them too.

Humans may be responsible for the spread of the fungus: Scientists suspect that it came from its home in South Africa when clawed frogs were exported 50 years ago for use in pregnancy tests. (A dose of a pregnant woman’s urine causes a female clawed frog to lay eggs within eight to 12 hours. The test also works on male frogs, which produce sperm in response to the injection.)

African clawed frogs are mostly resilient to chytrid, and probably carried the fungus, but frogs elsewhere have little defence. It can wipe out a species in a matter of years.

Poster children

The reason for their vulnerability boils down to two things: They spend part of their lives in water and part on land, so they are exposed to factors in both environments; and their skin – not scaly like a reptile’s, but soft, thin and permeable – renders them more sensitive to things such as ultraviolet radiation, pesticides and disease.

As the most threatened group of animals on the planet, they are not just poster children for the biodiversity crisis, they are also harbingers of things to come. Because amphibians occupy a unique and crucial place in the food chain, their extinctions will ripple through the ecosystem and catalyze the rapid disappearance of other animals, large and small.

Their young – salamander larvae and frog tadpoles – are major bottom feeders. When they grow into adults and move onto land, they bring nutrients from the water with them.

“Usually water is a trap for biomass,” says McGill University zoologist David Green, one of Canada’s foremost authorities on amphibian declines. Things flow from land into water easily in rain, but amphibians, which move back onto land as adults, are one of the very few things in nature that move nutrients in the reverse direction, back onto land. “That’s a very important job,” Prof. Green says.

Moreover, as adults, they consume huge numbers of insects, then themselves are consumed in huge numbers by larger animals, such as birds and mammals. If we take these middlemen out of the food chain, the consequences could be disastrous. Insect populations could explode, while birds and mammals may disappear.

Yet, despite their importance, conservationists are struggling to raise the funds they need to save them.

“A charismatic bird or mammal will easily draw in money, but it is hard to get funding for amphibians,” says Helen Meredith, who is leading the Zoological Society of London’s EDGE amphibian-conservation program.

The London Zoo is caring for and breeding a number of spectacular amphibians, including the golden poison frog, and is sponsoring projects overseas for highly endangered amphibians such as the giant Chinese salamander (hunted for its meat in China, where it is considered a delicacy) and the spectacularly ugly purple frog of India, discovered just last year.

EDGE – meaning “evolutionarily distinct and globally endangered” – has found that 85 of the most distinctive and endangered 100 amphibian species are receiving little to no conservation attention. “Amphibians have been pushed into the shadows,” Ms. Meredith says.

“But in terms of conservation dollars, you can accomplish so much more than investing in any of the large ‘charismatic’ mammals,” says Kevin Zippel, director of Amphibian Ark, a branch of the World Conservation Union, which is supporting captive breeding programs.

Breeding amphibians is comparatively simple. They are small and fairly easy to take care of. “For just $50,000 to $100,000, you can save an entire amphibian species from extinction. Compare that to the amount it costs to rent one panda for a year from China: $1-million, and that doesn’t even include housing, food and staff.”

Amphibian Ark is trying to raise $50-million for the captive management of 500 species. “If each of the world’s largest zoos just took on one species each, we’d be done,” Mr. Zippel says.

“Though we aren’t saying that having these species in glass boxes is an acceptable form of conservation – it’s just an option for the future,” he adds.

Arks to tombs

But unless more effort is put into restoring their wild habitats, the “arks will only become tombs,” says ecologist Alan Pounds, who has been documenting the decline of golden toads and harlequin frogs in Central America since the 1980s. “We can’t save the world with captive breeding. We have always thought that if we have parks and reserves, then we can do what we want with the rest of the planet – and that is not true.”

He says the spread of chytrid in the mountains of Costa Rica is tied to global warming. His research, published in the journal Nature, indicates that the fungus causes more frog deaths in warmer years, when the hilltops – normally cool – become more hospitable to the fungus.

And it is happening not just in the mountains of Central America: Other researchers have tied the spread of the fungus in midwife toads in Spain to a warming climate.

But chytrid occurs in many places without being lethal. McGill’s Prof. Green has found it in about 13 per cent of amphibians from five Canadian provinces. “Canada would have to get warmer and wetter” for the fungus to become lethal, he says. “We may start to see that.”

Even if this doesn’t happen, frogs all over Canada are disappearing. Leopard frogs on the Prairies are vanishing, and nobody quite knows why. Fowler’s toads may be driven out of their only range, in Southern Ontario, where they are mowed over by beach grooming machines sent to remove cigarette butts. Chorus frogs in Quebec, along with their songs, are fading because of suburban development.

The precise causes can be hard to pin down, but many studies have implicated UV radiation, low doses of pesticides and agricultural pollution. Most ecologists believe that it is rarely one single factor that is responsible, but the combination of threats.

Ecologist Pieter Johnson at the University of Colorado published a landmark study in 2007 in the Proceedings of the National Academy of Sciences (PNAS) demonstrating that the combination of fertilizer runoff in ponds and the flatworm parasite Ribeiroia ondatrae may be responsible for the high prevalence of amphibian mutations that we see all over the United States and Canada (up to 70 per cent of frogs in some wetlands grow multiple arms and legs). High levels of fertilizers in ponds spawn blooms of algae, which in turn foster an explosion in snails which carry the parasites.

Many other studies have found such “synergistic effects.” Researchers from Oregon State University have shown that the combination of UV radiation and fertilizer pollution kills seven times more frogs than either alone.

Ecologist Rick Relyea at the University of Pittsburgh, who studies pesticides, reported in 2001 in the PNAS that subjecting tadpoles to the fear of a caged predator in their tank, combined with low levels of the pesticide carbaryl, caused grey tree frog tadpoles (found in Canada) to die when neither factor alone killed them. “Many people were shocked and amazed,” he says.

He has an upcoming paper in the journal Ecological Applications that will show that combinations of low doses of pesticides – non-lethal on their own – are “highly lethal.”

But Prof. Relyea cautions that we cannot be sure pesticides are causing frog declines in the wild – more research is needed. “The problem is that an awful lot of effort goes into assessing the benefits of these chemicals, but not the costs.” We just need to be smarter about how we use pesticides, he says, such as spraying them in minimal amounts and at times of year when amphibians are less vulnerable – for example, after the tadpoles have grown into frogs.

If pesticides are responsible for deaths in the wild, the impact could be more widespread than we realize. Ecologists from the University of Toronto reported last year that pesticides in the soils in Costa Rica were actually more concentrated higher up the mountains than lower down closer to plantations, carried aloft by breezes and deposited onto the mountaintops when mists form at high elevations.

Chemical cocktails

There is an important lesson to be learned here: Being so sensitive, amphibians are sending us a warning signal. For good reason, they are known as our canaries in the coal mine. “If we lose the amphibians, then we lose our best detection system to see what’s going on with the world,” EDGE’s Ms. Meredith says.

And not only that, we also lose “our tools for future drug production,” she says. Frogs harbour incredible cocktails of chemicals in their skin that are being investigated by medical researchers. The lethal poisons of arrow frogs may be harnessed for antibiotics, and seem to yield effective painkillers hundreds of times more powerful than morphine. The wood frog, widespread in Canada, can freeze solid and survive, and is being probed for clues to preserve frozen organs during transplant. Salamanders, which can regenerate their limbs, may some day help us to grow lost digits. And it was discovered just three years ago that certain red-eyed tree frogs produce a protein that can block HIV infection.

“On the back of some toad somewhere is the compound that will do wonders for you, but we don’t know which one it is yet,” Prof. Green says.

Already we have lost amphibian species to extinction that may have been able to help us. In the 1970s, scientists discovered a species of frog in Australia that gestated its eggs in its stomach, using special hormones to shut down its digestive system. It could have held the clues to treat ulcers, but it has not been seen in decades.

Before the 3,000 amphibians in decline suffer the same fate, is there anything we can do? When we are trying to fight the battle on so many fronts, is there any way to win the war?

We need to deal with every single issue at once: climate change, excessive use of agricultural fertilizers and pesticides, depletion of the ozone layer and, above all, habitat degradation.

But the case isn’t hopeless, Prof. Green says, as long as we take action now. “We have to give amphibians some credit,” he says. “They are not so vulnerable and fragile. It’s just the combination of factors that they cannot cope with. They are tough as boots if you give them a chance.”

Zoe Cormier is a science writer based in London.

HIGHLY ENDANGERED

Chinese giant salamander

The largest amphibian in the world. Has declined massively since the 1960s.

Primary threat is hunting. Considered a delicacy in China.

Chile’s Darwin frog

Carries young in mouth. May already be extinct.

Panama Golden Frog

No longer in the wild. Being bred at the Toronto and Vancouver zoos. Communicates with hand waves.

Olm

Blind. Lives in caves. May be able to live for more than 100 years and go without food for 10.

Purple frog

Just discovered in 2003. Critically endangered. Wonderfully ugly.

Golden poison frog

Most poisonous vertebrate on Earth.

***

WONDERFUL AND WEIRD

Hairy frog of Cameroon

Just spectacularly gross.

Pac man frog

Unlike any other amphibian, possesses teeth. Actually eats mice.

Australian red-eyed tree frog

One of many species of “red-eyed” tree frogs, or “swimsuit calendar frogs.” Produces protein in skin that can block HIV.

Surinam toad

Breeds young embedded in its back.

Betic midwife toad

Carries eggs around in a ball around its legs.

Zoe Cormier

From globeandmail.com

Posted in Amphibians, Herpetology, International articles and news., Science/Scientific papers | 2 Comments »

Unique Adaptive Evolution Found In Snake Proteins Provide New Insight Into Vertebrate Physiology

Posted by Miqe on May 21, 2008

Prior to the advent of large sequence datasets, it was assumed that innovation and divergence at the morphological and physiological level would be easily explained at the molecular level. Molecular explanations for physiological adaptations have, however, been rare. Pollock and colleagues now provide evidence that major macroevolutionary changes in snakes (e.g., physiological and metabolic adaptations and venom evolution) have been accompanied by massive functional redesign of core metabolic proteins.

“The molecular evolutionary results are remarkable, and set a new precedence for extreme protein evolutionary adaptive redesign. This represents the most dramatic burst of protein evolution in an otherwise highly conserved protein that I know of,” said Dr. David Pollock, a professor of Biochemistry & Molecular Genetics at the University of Colorado Denver School of Medicine.

Over the last ten years, scientists have shown that snakes have remarkable abilities to regulate heart and digestive system development. They endure among the most extreme shifts in aerobic metabolism known in vertebrates. This has made snakes an excellent model for studying organ development, as well as physiological and metabolic regulation. The reasons that snakes are so unique had not previously been identified at the molecular level. In this recent study by Pollock and colleagues, the researchers show that mitochondrially-encoded oxidative phosphorylation proteins in snakes have endured a remarkable process of evolutionary redesign that may explain why snakes have such unique metabolism and physiology.

Amino acids that are normally highly conserved in these proteins have been altered, affecting key molecular functions such as proton transfer (which establishes a proton concentration gradient that drives energy production in the cell). In addition to the accelerated burst of amino acid replacements, evidence for adaptation comes from the remarkable levels of molecular coevolution and convergence that were observed.

The function of core oxidative metabolic proteins in vertebrates remains extremely controversial, mostly because of the difficulty of experimentally manipulating these membrane-embedded proteins. By integrating analyses of molecular evolution with protein structural data, the authors show that critical functions of mitochondrial proteins, such as the channeling of oxygen, electrons, and protons through cytochrome C oxidase, have been fundamentally altered during the evolution of snakes. Snakes have been previously proposed as an ideal metabolic, physiological, and ecological model system to study evolution, and the current results support that idea, showing that their utility as a model system can extend to the molecular level.

“Snakes are an invaluable resource for structural biologists and biochemists, who can use comparative genomics to generate hypotheses on how COI and oxidative phosphorylation function, and how these functions may be altered and redesigned,” said Dr. Todd Castoe, a lead author on the paper.

“We believe that our results will provide a textbook case as the most clear and dramatic example of adaptive evolution in a core metabolic protein to date, as well as providing the implication that strong molecular and physiological adaptation can be linked,” said Pollock.

“The manuscript represents an important milestone in molecular evolution and vertebrate adaptation, and opens up clear and well-justified directions for further research. Snake metabolic proteins may significantly clarify understanding about the operation of these critical yet functionally elusive metabolic proteins.”

Funding was provided through an NIH training grant and other NIH grants. These funding sources had no role whatsoever in preparation of the manuscript.

From ScienceDaily

Posted in Herpetology, Herps in the news, International articles and news., Reptiles, Science/Scientific papers, Snakes | 4 Comments »

Still just a lizard

Posted by Miqe on May 16, 2008

I found a blogpost that I can´t help myself from sharing with you..

podarcis.jpg

“The title gets the principal objection of any creationist out of the way: yes, this population of Podarcis sicula is still made up of lizards, but they’re a different kind of lizard now. Evolution works.

Here’s the story: in 1971, scientists started an experiment. They took 5 male lizards and 5 female lizards of the species Podarcis sicula from a tiny Adriatic island called Pod Kopiste, 0.09km2, and they placed them on an even tinier island, Pod Mrcaru, 0.03km2, which was also inhabited by another lizard species, Podarcis melisellensis. Then a war broke out, the Croatian War of Independence, which went on and on and meant the little islands were completely neglected for 36 years, and nature took its course. When scientists finally returned to the island and looked around, they discovered that something very interesting had happened.

The original population of P. sicula was still present on Pod Kopiste, so we have a nice control population. These lizards are small, fast, insect-eaters in which the males defend territories.

Sadly, P. melisellensis on Pod Mrcaru had been extirpated. So we had a few innocent casualties of the experiment.

The transplanted P. sicula thrived and swarmed over the island of Pod Mrcaru, but they were different, and they had evolved in multiple ways.

The original P. sicula were insectivores who occasionally munched on a leaf; approximately 4-7% of their diet was vegetation. The P. sicula of Pod Mrcaru, though, had adopted a more vegetarian diet: examining their gut contents revealed that 34% of their diet was plants in the spring, climbing to 61% in the summer…and much of this diet was hard-to-digest stuff, high in cellulose. This is a fairly radical shift.

There were concomitant changes. The lizards’ skulls were wider, deeper, and longer, and they had stronger bites — a necessity for chomping off bits of tough plants, instead of soft mosquitos. Instead of chasing bugs, they’re browsing stationary plants, and their legs are shorter and they are slower. Population densities are higher. The Pod Mrcaru lizards no longer seem to defend territories, so there have been behavioral changes.

Still just a lizard, I know.

Now here’s something really cool, though: these lizards have evolved cecal valves. What those are are muscular ridges in the gut that allow the animal to close off sections of the tube to slow the progress of food through them, and to act as fermentation chambers where plant material can be broken down by commensal organisms like bacteria and nematodes — and the guts of Pod Mrcaru P. sicula are swarming with nematodes not found in the guts of their Pod Kopiste cousins.

Here’s a photo (how could I resist an opportunity to show some lizard guts?). The top ones may be a little difficult to interpret; what they’ve done is slit open the tube of the gut, and then use some pins to hold the tube open so you can see the little ridge or flap that rings the interior.

The cecal valves are an evolutionary novelty, a brand new feature not present in the ancestral population and newly evolved in these lizards. That’s important. This is more than a simple quantitative change, but is actually an observed qualitative change in a population, the appearance of a new morphological structure.

Evolution created something new, and it did it quickly (about 30 generations), and the appearance was documented. It’s still just a lizard, but we expected nothing else — and it’s now a lizard with novel adaptations for herbivory.”

From Pharyngula`s blog.

Posted in Fieldherping, Herpetology, Herps in the news, International articles and news., Lizards, Reptiles, Science/Scientific papers | Tagged: , | Leave a Comment »

 
Follow

Get every new post delivered to your Inbox.