Friday, February 27, 2015

Chytrid fungus detected in Madagascar frog species

Chytrid fungus was proved present on Platypelis pollicaris
from Ranomafana. Photo Credit: Miguel Vences / TU 
Braunschweig
The chytrid fungus, which is fatal to amphibians, has been detected in Madagascar for the first time. This means that the chytridiomycosis pandemic, which has been largely responsible for the decimation of the salamander, frog and toad populations in the USA, Central America and Australia, has now reached a biodiversity hotspot. The island in the Indian Ocean is home to around 290 species of amphibians that are not found anywhere else in the world. Another 200 frog species that have not yet been classified are also thought to live on the island. Researchers from the Helmholtz Centre for Environmental Research (UFZ) and TU Braunschweig, together with international colleagues, are therefore proposing an emergency plan. This includes monitoring the spread of the pathogenic fungus, building amphibian breeding stations and developing probiotic treatments, say the scientists, writing in Scientific Reports, the acclaimed open-access journal from the publishers of Nature.

The entire amphibian class is currently afflicted by a global pandemic that is accelerating extinction at an alarming rate. Although habitat loss caused by human activity still constitutes the main threat to amphibian populations, habitat protection no longer provides any guarantee of amphibian survival. Infectious diseases are now threatening even seemingly secluded habitats. The most devastating of the known amphibian diseases is chytridiomycosis, which is caused by a deadly chytrid fungus (Batrachochytrium dendrobatidis, or Bd). The fungus attacks the skin, which is particularly important in amphibians because they breathe through it. A large number of species have already been lost in this way -- particularly in tropical Central America, where two-thirds of the colorful harlequin frog species have already been decimated across their entire area of distribution. Bd has now been identified in over 500 amphibian species, 200 of which have seen a significant decline in numbers. The pathogen is therefore classified worldwide as one of the greatest threats to biodiversity.

Until now, however, a few islands like Madagascar were thought not to have been affected. The last series of tests from 2005 to 2010 found no trace of the pathogenic fungus there. However, an analysis of the latest series of tests shows that the chytrid fungus also poses a threat to amphibians in Madagascar. "This is sad news for amphibian-lovers around the world," says Dr Dirk Schmeller of the UFZ, who was involved in analyzing the samples. "Firstly, it means that an island that is home to a particularly high number of amphibian species is now at risk. Several hundred species live only on this island. And, secondly, if the pathogen has managed to reach such a secluded island, it can and will occur everywhere."

For the study that has just been published, the research team analyzed samples from over 4000 amphibians from 50 locations in Madagascar taken since 2005. Samples from four species of Madagascan frog (Mantidactylus sp.) taken in 2010, and from one Mascarene frog (Ptychadena mascareniensis) taken in 2011 from the remote Makay massif tested positive for the fungus. In samples from 2013 and 2014 the pathogen was found in five different regions. Prof. Miguel Vences from TU Braunschweig says, "The chytrid fungus was found in all four families of the indigenous Madagascan frogs, which means it has the potential to infect diverse species. This is a shock!" The study also shows that the disease affects amphibians at medium to high altitudes, which ties in with observations from other parts of the world, where the effects of the amphibian epidemic have been felt primarily in the mountains.

The fact that the fungus has been identified in a very remote part of the island has puzzled the researchers. There is some hope that it may prove to be a previously undiscovered, native strain of the pathogen, which may have existed in the region for some time and have gone undetected because of a lack of samples. In this case, Madagascar's amphibians may have developed resistance to it. However, further research is needed to confirm this hypothesis before the all-clear can be given. It is also possible that the fungus was brought to the island in crustaceans or the Asian common toad (Duttaphrynus melanostictus), carried in by migratory birds or humans. "Luckily, there have not yet been any dramatic declines in amphibian populations in Madagascar," Dirk Schmeller reports. "However, the pathogen appears to be more widespread in some places than others. Madagascar may have several strains of the pathogen, maybe even the global, hypervirulent strain. This shows how important it is to be able to isolate the pathogen and analyze it genetically, which is something we haven't yet succeeded in doing." At the same time, the researchers recommend continuing with the monitoring program across the entire country to observe the spread of the disease. The scientists also suggest setting up extra breeding stations for key species, in addition to the two centers already being built, to act as arks, so that enough amphibians could be bred to recolonize the habitats in a crisis. "We are also hopeful that we may be able to suppress the growth of the Bd pathogen with the help of skin bacteria," says Miguel Vences. "It might then be possible to use these bacteria as a kind of probiotic skin ointment in the future." A high diversity of microbial communities in the water could also reduce the potential for infection, according to earlier investigations conducted by UFZ researchers and published in Current Biology.

The outbreak of amphibian chytridiomycosis in Madagascar puts an additional seven per cent of the world's amphibian species at risk, according to figures from the Amphibian Survival Alliance (ASA). "The decline in Madagascan amphibians is not just a concern for herpetologists and frog researchers," says Dr Franco Andreone from the International Union for Conservation of Nature (IUCN), who is one of the study authors. "It would be a great loss for the entire world." In the coming months, the scientists therefore plan to work with the government to draw up an emergency plan to prevent this scenario.

Citation
Bletz MC, Rosa GM, Andreone F, Courtois EA, Schmeller DS, Rabibisoa NHC, Rabemananjara FCE, Raharivololoniaina L, Vences M, Weldon C, Edmonds D, Raxworthy CJ, Harris RN, Fisher MC, Crottini A. Widespread presence of the pathogenic fungus Batrachochytrium dendrobatidis in wild amphibian communities in Madagascar. Scientific Reports, 2015; 5: 8633 DOI:10.1038/srep08633


Thursday, February 26, 2015

A Miocene radiation of crocs in the Pebas Wetland

The massive wetlands once covered the Amazon River basin about
13 million years ago during the late middle Miocene. Three newly
discovered species of crocodylians, including Kuttanacaiman
iquitosensis (left), Caiman wannlangstoni (right) and Gnatusuchus
pebasensis (bottom), look for clams, which they could likely scoop up
with their mouths and crunch with their peglike teeth.
Artist Credit: Javier Herbozo


Thirteen million years ago, as many as seven different species of crocodiles hunted in the swampy waters of what is now northeastern Peru, new research shows. This hyperdiverse assemblage, revealed through more than a decade of work in Amazon bone beds, contains the largest number of crocodile species co-existing in one place at any time in Earth's history, likely due to an abundant food source that forms only a small part of modern crocodile diets: mollusks like clams and snails. The work, published today in the journal Proceedings of the Royal Society B, helps fill in gaps in understanding the history of the Amazon's remarkably rich biodiversity.

"The modern Amazon River basin contains the world's richest biota, but the origins of this extraordinary diversity are really poorly understood," said John Flynn, Frick Curator of Fossil Mammals at the American Museum of Natural History and an author on the paper. "Because it's a vast rain forest today, our exposure to rocks--and therefore, also to the fossils those rocks may preserve--is extremely limited. So anytime you get a special window like these fossilized "mega-wetland" deposits, with so many new and peculiar species, it can provide novel insights into ancient ecosystems. And what we've found isn't necessarily what you would expect."

Before the Amazon basin had its river, which formed about 10.5 million years ago, it contained a massive wetland system, filled with lakes, embayments, swamps, and rivers that drained northward toward the Caribbean, instead of today's pattern of eastward river flow to the Atlantic Ocean. Knowing the kind of life that existed at that time is crucial to understanding the history and origins of modern Amazonian biodiversity. But although invertebrates like mollusks and crustaceans are abundant in Amazonian fossil deposits, evidence of vertebrates other than fish have been very rare.

Since 2002, Flynn has been co-leading prospecting and excavating expeditions with colleagues at fossil outcrops of the Pebas Formation in northeastern Peru. These outcrops have preserved life from the Miocene, including the seven species of crocodiles discussed in Proceedings B. Three of the species are entirely new to science, the strangest of which is Gnatusuchus pebasensis, a short-faced caiman with globular teeth that is thought to have used its snout to "shovel" mud bottoms, digging for clams and other mollusks. The new work suggests that the rise of Gnatusuchus and other "durophagous," or shell-crunching, crocodiles is correlated with a peak in mollusk diversity and numbers, which disappeared when the mega-wetlands transformed into the modern Amazon River drainage system.

"When we analyzed Gnatusuchus bones and realized that it was probably a head-burrowing and shoveling caiman preying on mollusks living in muddy river and swamp bottoms, we knew it was a milestone for understanding proto-Amazonian wetland feeding dynamics," said Rodolfo Salas-Gismondi, lead author of the paper and a graduate student at the University of Montpellier, in France, as well as researcher and chief of the paleontology department at the National University of San Marcos' Museum of Natural History in Lima, Peru.

Besides the blunt-snouted crocodiles like Gnatusuchus, the researchers also recovered the first unambiguous fossil representative of the living smooth-fronted caiman Paleosuchus, which has a longer and higher snout shape suitable for catching a variety of prey, like fish and other active swimming vertebrates.

Besides the blunt-snouted caimanines with crushing dentition and stout jaws, and smooth-fronted caiman Paleosuchus, which possesses a relatively more generalist snout shape the authors report other caimanines with more specialized feeding habits. They included the following. The larger Purussaurus neivensis and Mourasuchus atopus (both previously known from other Miocene localities in the region). Purussaurus had a hulking skull and a mandible with large robust anterior teeth and smaller blunt posterior teeth. The ‘duck-faced’ taxon Mourasuchus had an exceptionally long, wide rostrum. Its feeding habits are controversial, although previous authors thought it ate small fishes by some kind of filtering strategy. A new, unnamed gavialoid is the only crocodylian with a longirostral morphotype in this community, a fact that contrasts with the high diversity of longirostrine crocodylians characteristic of Late Miocene Neotropical assemblages.

"We uncovered this special moment in time when the ancient mega-wetland ecosystem reached its peak in size and complexity, just before its demise and the start of the modern Amazon River system," Salas-Gismondi said. "At this moment, most known caiman groups co-existed: ancient lineages bearing unusual blunt snouts and globular teeth along with those more generalized feeders representing the beginning of what was to come."

The new research suggests that with the inception of the Amazon River System, mollusk populations declined and durophagous crocodile species went extinct as caimans with a broader palate diversified into the generalist feeders that dominate modern Amazonian ecosystems. Today, six species of caimans live in the whole Amazon basin, although only three ever co-exist in the same area and they rarely share the same habitats. This is in large contrast to their ancient relatives, the seven diverse species that lived together in the same place and time.

Citation

Salas-Gismondi R, Flynn JJ, Baby P, Tejada-Lara JV, Wesselingh FP, Antoine P-O. 2015. A Miocene hyperdiverse crocodylian community reveals peculiar trophic dynamics in proto-Amazonian mega-wetlands. Proceedings of the Royal Society B  DOI: 10.1098/rspb.2014.2490

Wednesday, February 25, 2015

New drug potential from Heloderma

Heloderma suspectum

Lizards and other reptiles are not normally considered venomous, but a number of lizard species actually do produce and use venom. The most classic venomous lizard is no doubt the gila monster -- a heavy-bodied lizard. As the first in the world, a group of researchers has made a comprehensive description of the proteins in the venom which can prove to be relevant in connection with developing new types of drugs.

Gila and beaded lizards are the classic venomous lizards. However, it was recently shown that venom is also used by a number of other species, such as the awesome Komodo monitors -- the largest present-day lizards. Lizard venom has much in common with snake venom, and the current theory is that the venom production apparatus in lizards and snakes is related, but has developed in different directions. Gila and beaded lizards mainly use venom to defend themselves, while snakes use their venom to attack prey. However, the composition of venom proteins is similar in lizards and snakes.

Venom research is a large field, especially due to the pharmaceutical potential of the venom proteins. The idea here is that venom proteins are capable of affecting the body's cells. Excessive amounts can be harmful and even lethal in some circumstances, but if the right dose is used, the venom proteins can be used to treat certain diseases. Snake proteins that normally cause prey to bleed can be used in small doses to treat blood clots, for example. In the same way, work is currently being done to develop spider venom proteins to provide pain relief. The Aarhus researchers focused on Gila lizards, and these are currently being used in pharmaceutical contexts. Gila lizards produce exendin-4, a small venom protein used in the treatment of diabetes and obesity, which is a competitor to Victoza® -- produced by Novo Nordisk.

A method called proteomics was used in the Aarhus study to make the first overall description of venom proteins in Gila lizards. Individual proteins such as exendin-4 used to be purified from Gila lizard venom, and this resulted in a number of interesting results. However, an overall analysis of all the venom proteins has not been undertaken before, which therefore made it easy to overlook the potentially important components in the venom.

Making a comprehensive analysis of the venom protein composition was not an easy task. "The work was complicated by the fact that the Gila lizard genome hasn't been isolated, and genomes normally provide a map to navigate when you're using proteomics for protein identifications," says Associate Professor Kristian Wejse Sanggaard. "We therefore used a more manually based approach to identify the proteins in the Gila lizard venom. This succeeded, and we've identified nineteen proteins that no one previously knew existed in the venom," he concludes.

Based on these identifications, the researchers have gained new knowledge about the function of the venom proteins, and have also gained greater insight into the evolutionary contexts of venom proteins. In addition, there are now new proteins that can potentially be used to develop future drugs.

Citation
Sanggaard KW, Dyrlund TF, Thomsen LR, Nielsen TA, Brøndum L, Wang T, Thøgersen IB, Enghild JJ. Characterization of the gila monster (Heloderma suspectum suspectum) venom proteome. Journal of Proteomics, 2015; 117: 1 DOI: 10.1016/j.jprot.2015.01.004


Thursday, February 19, 2015

The Spider-tailed Viper in action

The following video was sent to me by Patrick Prévost (Amneville Zoo, France). Video of captives moving their tail on a sand substrate have been available on You-Tube. This video shows a snake catching a bird. Sorry about the ad!


La vipère araignée by Spi0n

A second chance for two Australian sea snakes (Aipysurus) presumed extinct

Photographs A,C: A. apraefrontalis (SAMA R68142)
from Ashmore Reef; and B, D:Aipysurus foliosquama
(WAM R150365) from Barrow Island.
One in five reptile species are estimated to be at risk of extinction and many are thought to have become extinct within the last 50 years. Threats to reptiles include habitat loss and degradation, climate warming, and overharvest for food, traditional medicines and leather. Rediscoveries of presumed extinct species inspire optimism, but many such rediscovered species remain at immediate risk of extinction and require urgent assessment of population status and threats in their remaining range to guide management actions.

In a new paper published in PLoS ONE, Sanders, Schroeder, Guinea and Rasmussen (2015) report on the critically endangered leaf-scaled (Aipysurus foliosquama) and short-nosed (A. apraefrontalis) sea snakes. Species currently recognized only from Ashmore and Hibernia reefs ~600km off the northwest Australian coast. Steep population declines in both species were documented over 15 years and neither has been sighted on dedicated surveys of Ashmore and Hibernia since 2001. The authors examine specimens of these species that were collected from coastal northwest Australian habitats up until 2010 (A. foliosquama) and 2012 (A. apraefrontalis) and were either overlooked or treated as vagrants in conservation assessments. Morphological variation and mitochondrial sequence data confirm the assignment of these coastal specimens to A. foliosquama (Barrow Island, and offshore from Port Hedland) and A.apraefrontalis (Exmouth Gulf, and offshore from Roebourne and Broome). Collection dates, and molecular and morphological variation between coastal and offshore specimens, suggest that the coastal specimens are not vagrants as previously suspected, but instead represent separate breeding populations. The newly recognized populations present another chance for leaf-scaled and short-nosed sea snakes, but the coastal habitats in northwest Australia are threatened by infrastructure developments and sea snakes are presently omitted from environmental impact assessments for industry. The authors note further studies are urgently needed to assess these species’ remaining distributions, population structure, and extent of occurrence in protected area.

Citation

Sanders KL, Schroeder T, Guinea ML, Rasmussen AR (2015) Molecules and Morphology Reveal Overlooked Populations of Two Presumed Extinct Australian Sea Snakes (Aipysurus: Hydrophiinae). PLoS ONE 10(2): e0115679. doi:10.1371/journal.pone.0115679.




Body size and extinction

 

A new University of Toronto study may force scientists to rethink what is behind the mass extinction of amphibians occurring worldwide in the face of climate change, disease and habitat loss.

The old cliché "size matters" is in fact the gist of the findings by graduate student Stephen De Lisle and Professor Locke Rowe of U of T's Department of Ecology & Evolutionary Biology in a paper published today in Proceedings of the Royal Society B.

By examining research on global patterns of amphibian diversification over hundreds of millions of years, De Lisle and Rowe discovered that "sexually dimorphic" species -- those in which males and females differ in size, for example -- are at lower risk of extinction and better able to adapt to diverse environments.

Their work suggests the ability of males and females in sexually dimorphic amphibian species to independently evolve different traits -- such as size -- helps them survive extinction threats that kill off others, says De Lisle.

He says classic ecological theory would not have predicted that about amphibians, a class of vertebrates that includes frogs, toads, salamanders, newts and caecilians.

The conventional school of thought believes different-sized sexes of the same species take up more resources and are less able to adapt and diversify than species where ecologically relevant traits like size are basically the same between males and females.

"I think if our results bear on mass extinction at all, it suggests we maybe should start looking more closely at the traits of some of the species that are going extinct," says De Lisle.

"Scientists might start thinking in a new way about how other traits, like sex differences in habitat use or diet, might play a role."

While peacock feathers or deer antlers are understood to help males of those species successfully mate, less is understood about amphibians, which are being wiped out so fast many are going extinct before scientists can identify them.

Some estimate between 30 and 40 per cent of the world's approximately 7,000 species of amphibians are currently in danger of extinction -- more than any other animals on earth -- and their decline is a critical threat to global biodiversity.

Many scientists believe amphibians serve as "canaries in a coal mine," and declines in their populations indicate other groups of animals and plants will soon be at risk.

Amphibians are not only an important part of the food chain and biodiversity. Some have chemicals in their skins that can be developed into medicines to fight diseases such as cancer and perhaps even AIDS.

Because their skins are highly permeable and they have a two-staged life cycle that starts in water and then moves to land, amphibians may be more susceptible to temperature changes, water and air pollution than other animals.

The new study by De Lisle and Rowe adds another piece to the puzzle about why some species are doing well while others are in decline or disappearing.

For example, both the golden toad and the harlequin frog of Costa Rica's Monteverde Cloud Forest Preserve disappeared completely in the late 1980s despite living in what was considered a pristine habitat.

"Our work suggests we still maybe don't have the best understanding of what traits might be influencing these extinctions, although now we have the understanding that sexual dimorphism is an important trait," says De Lisle.

Citation
Stephen P. De Lisle, Locke Rowe. Independent evolution of the sexes promotes amphibian diversification. Proceedings of the Royal Society B, February 2015 DOI: 10.1098/rspb.2014.2213


Monday, February 9, 2015

Coral snake venom targets GABA(A) receptors

The rare coral snake Micrurus mipartitus (type locality, Caracas, 
Venezuela). Credit: Alejandro Solórzano
For more than a decade, a vial of rare snake venom refused to give up its secret formula for lethality; its toxins had no effect on the proteins that most venoms target. Finally, an international team of researchers figured out its recipe: a toxin that permanently activates a crucial type of nerve cell protein, preventing the cells from resetting and causing deadly seizures in prey. The details will be published online in the Proceedings of the National Academy of Sciences the week of Feb. 9.

"What we found are the first known animal toxins, and by far the most potent compounds, to target GABA(A) receptors," says Frank Bosmans, Ph.D., assistant professor of physiology and neuroscience at the Johns Hopkins University School of Medicine. "Once they bind to the receptors, they don't let go."

Biochemical studies revealed the identity of the venom's active ingredient: it's actually twin proteins, dubbed micrurotoxins (MmTX) after their serpentine source, the reclusive coral snake Micrurus mipartitus. Most toxins in snake venoms target specialized nicotinic acetylcholine receptors on the surface of nerve cells that make muscles contract, paralyzing the snakes' victims. But when the researchers tested MmTX on lab-grown cells saturated with nicotinic acetylcholine receptors, nothing happened. This was puzzling because, in mice, MmTX was known to cause a repeating pattern of relaxation and seizures, similar to what's seen in epilepsy.

By tagging the protein with a radioactive label, the team at Aix Marseille University was able to find out what protein it acted on. To the team's surprise, MmTX binds to GABA(A) receptors -- pores on nerve cells in the brain and spinal cord. GABA(A) receptors' job is to respond to the molecule GABA by opening to let negatively charged chloride ions flow into a nerve cell that has just fired. Doing so resets the cell's equilibrium so that it can fire another signal when needed.

Further testing showed that MmTX binds to GABA(A) receptors more tightly than any other compound known -- 100 times tighter than the plant-derived compound PTX, for example. MmTX also binds to a unique site on the GABA(A) receptor protein. Binding at that site changes the receptor's shape, making it far too sensitive to GABA molecules. When GABA binds, the receptor's pore opens permanently and the nerve cell is never able to reset, causing it to misfire, convulsing the animal and potentially causing death.

"Anti-anxiety medications like diazepam and alprazolam bind to GABA(A) receptors too, but they cause relaxation instead of seizures because they bind much more loosely," says Bosmans. His team plans to use MmTX as a tool for learning more about how GABA(A) receptors work. Since errors in the receptors can cause epilepsy, schizophrenia and chronic pain, the team hopes that their future work will be able to shed light on these and other disorders.

Other authors of the report include Jean-Pierre Rosso, Brigitte Ceard and Pierre Bougis of Aix Marseille University in France; Jurgen Schwarz and Matthias Kneussel of the University Medical Center Hamburg-Eppendorf in Germany; Marcelo Diaz-Bustamante of The Johns Hopkins University; Maria Gutierrex of the Universidad de Costa Rica; and Olaf Pongs of the Universitat des Saarlandes in Germany.

This work was supported by the Centre National de la Recherche Scientifique.

Citation

Rosso J-P, Schwarz JR, Diaz-Bustamante M, Céard B, Gutiérrez JM, Kneussel M, Pongs O, Bosmans F, and Bougis PE. MmTX1 and MmTX2 from coral snake venom potently modulate GABAA receptor activity. PNAS February 9, 2015 DOI: 10.1073/pnas.1415488112.