Los cuerpos calientes protegen a las ranas de las enfermedades

By following individual frogs in the rainforest, we reveal that hot frogs are less likely to be infected with a potentially deadly fungus.

The Stoney Creek Frog (Litoria lesueuri complex) spends much of its time above the optimal growth temperature range of the amphibian chytrid fungus pathogen (17-25°C), and has not experienced population declines due to the disease chytridiomycosis. © Jodi J. L. Rowley.

The amphibian chytrid fungus (Batrachochytrium dendrobatidis) is responsible for the often fatal amphibian disease chytridiomycosis. This disease has now been associated with declines and extinctions in hundreds of species of amphibians worldwide, and is a serious threat to global amphibian biodiversity.

However, not all amphibian species decline from chytridiomycosis, and many amphibians that have declined from the disease in some environments coexist with it in others. Why might this be?
 

One such reason is temperature. In the lab, the amphibian chytrid fungus grows best between 17-25°C and infected captive frogs can be cured by simply raising the temperature. Natural populations of frogs also appear to be affected by temperature, with infected frogs more often detected in cooler months and at higher (and therefore cooler) altitudes. So there’s reason to suspect that temperature may play an important role in determining whether individual frogs are infected with the amphibian chytrid fungus in nature.

To investigate this, a small team of volunteers and I tracked over 100 frogs of three species in the rainforests of northeastern Australia. Each frog was fitted with a tiny radio-transmitter or diode attached via a tailor-made waist-belt that allowed us to find each frog every day and night for up to 16 days at a time. This was no easy feat in steep, boulder-strewn streams surrounded by dense (and often prickly!) vegetation. Once we located each frog, we recorded its body temperature (using an infrared gun or thermally sensitive radio-transmitter). This was also often rather tricky- just because the transmitter is telling you the frog is close, it doesn’t mean that it’s easy to see. Frogs that sit on rocks tend to look like rock, and frogs that sit on leaves have a tendency to look like leaves!

Although frogs were often located in the same parts of the same stream (with the same air temperature), the body temperatures of individual frogs varied considerably among and within individuals. A frog sitting under a boulder in the stream was a whole lot cooler than a frog basking in the sun ten metres up a tree or sitting on a sun-warmed rock.

The Endangered Waterfall Frog (Litoria nannotis) disappeared from many sites during epidemics of the disease chytridiomycosis in the late 1980′s and early 1990′s. This species spends little time above the optimal growth temperature range of the amphibian chytrid fungus pathogen (17-25°C). © Jodi J. L. Rowley.

The results of our intensive frog-stalking revealed that the more time individual frogs were found at temperatures above 25°C, the less likely they were to be infected by the amphibian chytrid. Frogs of all species were very unlikely to be infected if 75% or more of their body temperatures were above 25°C. This is the first demonstration that individual frog thermal histories affect the probability of amphibian chytrid infection in nature.

Our findings also point towards one possible way to reduce the impact of the disease on threatened amphibians in nature. By carefully manipulating habitats to increase the availability of warmer temperatures, we may be able to help frogs reach temperatures that allow them to reduce or eliminate infection. While at first glance, our findings may suggest that global climate change may act in favour of amphibians, it’s too complicated to predict. The impacts of global climate change, particularly at the small scales relevant to a frog, are likely to vary among species and sites. While increased air temperatures at some sites might decrease disease impact, increased cloud or canopy cover may increase it.

Reference: Rowley, J.J.L. & Alford, R.A. Hot bodies protect amphibians against chytrid infection in nature. Scientific Reports 3, 1515;DOI:10.1038/srep01515 (2013). (OPEN ACCESS)

Research from the School of Marine and Tropical Biology at James Cook University and the Australian Museum.

Top Photo: Green Eyed Tree Frog with radio-transmitter © Jodi J L Rowley

Invasion de Lithobates catesbeianus (Rana toro) en la Argentina

Chicos acá les dejo un artículo del grupo de herpetologia que viene siguiendo y trabajando a pulmon contra la expansion de la rana toro en nuestro país. Es el grupo de Eduardo Sanabria, quien inicialmente registraron la presencia de la especie en su provincia, San Juan y trabajaron a campo y con educacion ambiental en su combate. Ahora, el artículo publicado en "Cuadernos de Herpetología" recientemente comenta el primer registro de la especie en la provincia de Mendoza.
Lithobates catesbeianus en Mendoza

El genoma de anuros conlleva una esperanza de salvación

Frog genome holds out conservation promise
By Richard Black Environment correspondent, BBC News
Xenopus tropicalis The western clawed frog joins an illustrious list of sequencees

Scientists have published the first genome sequence from an amphibian.

Xenopus tropicalis, the western clawed frog, joins the list of sequenced organisms that includes chicken, horse, rat, yeast, platypus, and human being.

It has about 20,000 genes - about the same as a human - and scientists say it sheds new light on genetic evolution.

Conservationists say analysing the genes could lead to new ways of combating threats such as the often fatal fungal disease chytridiomycosis.

Presenting their results in the journal Science, the researchers also suggest it may lead to better understanding of the threat posed by endocrine-disrupting ("gender-bending") chemicals, to which amphibians are especially sensitive.
Filling the gap

Forty-eight scientists from 20 institutions collaborated on the study, led from the US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California.
Continue reading the main story

More detail on the genes that give resistance could have massive implications for captive breeding programmes

Robin Moore Conservation International

"When human genome work was wrapping up around 2002, we were discussing what should be next," JGI's Uffe Hellsten told BBC News.

"At that time there were a couple of furry mammals in the pipeline, and the chicken and at least two fish - but there seemed to be a gaping hole in the branch that constitutes the amphibians, and it seemed logical to fill that hole."

The species chosen - X tropicalis - is a close relative of a standard laboratory animal, the African clawed frog X laevis.

This animal has been a staple of pioneering research in fields such as cell differentiation, the role of ribonucleic acid (RNA) and cloning.

During the 1940s and 50s, their sensitivity to human hormones also led to their use in pregnancy tests.

For this project, X tropicalis was preferred because it reproduces much faster than its more famous cousin.
The chytrid fungus is devastating amphibians numbers around the world

Its genome is also roughly half the size.

That is because at some point in evolutionary history, the lineage leading to X laevis duplicated its DNA, meaning it now carries a double cargo of the double helix.

The team reports that certain regions of the genome, clustered around specific genes, are remarkably similar to equivalent regions in the genomes of chicken and Homo sapiens - despite the fact that their lineages diverged some 360 million years ago.

"When you look at segments of the Xenopus genome, you literally are looking at structures that are 360 million years old," said Dr Hellsten.

"They were part of the genome of the last common ancestor of all birds, frogs, dinosaurs and mammals that ever roamed the Earth."
Immune attack

However, it is the set of genes unique to amphibians that has excited conservationists.

For the last few decades, frogs and - to a lesser extent - salamanders have been hard hit by a water-borne fungus, Batrachochytrium dendrobatidis.

It is spreading across the world and has caused mass deaths in many species. It is implicated as the major factor in several species extinctions.
WHAT ARE AMPHIBIANS?
Continue reading the main story Salamanders

* First true amphibians evolved about 250m years ago
* Adapted to many different aquatic and terrestrial habitats
* Present today on every continent except Antarctica
* Undergo metamorphosis, from larvae to adults

Recently, scientists in several institutions have been working on a conservation strategy that would take naturally-occurring anti-chytrid chemicals from species that are immune, and use them to protect others.

Xenopus appear to be immune themselves; and unravelling the genetic blueprint of its chemical defences could perhaps help to accelerate this line of research.

"Xenopus is the genus from which chytrid was first recorded, in [a museum specimen from] 1938, and they seem to be resistant," said Robin Moore, amphibian conservation officer with Conservation International.

"More detail on the genes that give resistance could also have massive implications for captive breeding programmes, helping us select animals that are resistant."

A valuable next step, he added, would be to compare variants of these genes between amphibian species - especially from those that are highly vulnerable to chytrid.

Dr Hellsten also suggested the sequences could shed light on the mechanism of endocrine-disrupting chemicals such as polychlorinated biphenyls (PCBs) - colloquially known as "gender-benders" - which impact many animals, but amphibians in particular because of their skin's high permeability.

"Understanding the effects of these hormone disruptors will help us preserve frog diversity and, since these chemicals also affect humans, could have a positive effect on human health," he said.

http://news.bbc.co.uk/2/hi/science_and_environment/10090225.stm

La primera secuenciación completa del ADN de un anuro provee claves sobre la evolución del genoma de los vertebrados

Frog DNA Yields Clues to Vertebrate Genome Evolution
de Elizabeth Pennisi

Add another group of animals to the growing menagerie of creatures whose genomes have been sequenced. On page 633 of this week's issue of Science, researchers describe the sequence of the Western clawed frog, Xenopus tropicalis, the first member of the amphibian branch of the tree of life to be so honored. Researchers chose X. tropicalis to be the first amphibian sequenced because developmental biologists use it in their studies and it has a relatively small genome: 1.7 billion bases stretched across 10 chromosomes, about half the size of the human genome. Now, researchers are hungry for more.
Science 30 April 2010:
Vol. 328. no. 5978, p. 555
más info: http://www.sciencemag.org/cgi/content/full/328/5978/555