Showing posts with label anurans. Show all posts
Showing posts with label anurans. Show all posts

Friday, December 9, 2011

Odorrana Frogs as a Source for New Antibiotics

The  Chinese Odorrana tormota. Photo Credit 
Albert Feng
About 45 species of ranid frogs are currently recognized in the genus Odorrana, they inhabit high-gradient streams in Asia from Myanmar and Thailand and Malaya southward through the Sunda Shelf (Sumatra to Borneo) and eastward into China and Japan. And at least some species use ultrasonic sound to communicate through the noise of running water. Now, Yang et al. (2011) find that they may produce the greatest known variety of anti-bacterial substances known, and that they hold promise for becoming new weapons in the battle against antibiotic-resistant infections. The dorous frogs have been described as smelling like decomposing flesh. Zhang's research group at the Kunming Institute of Zoology, of the Chinese Academy worked to identify the specific antimicrobial peptides (AMPs) for developing new antibiotics. They identified more than 700 of these substances from nine species of odorous frogs and concluded that the AMPs account for almost one-third of all AMPs found in the world, the greatest known diversity of these germ-killing chemicals. Interestingly, some of the AMPs have a dual action, killing bacteria directly and simultaneouly activating the immune system. Their results sugest that identical AMPs were widely distributed in odorous frogs; 49 known AMPs can be found in different amphibian species. Purified peptides showed a strong and effective antimicrobial activity against four tested strains of microbe. They synthesized another 23 peptides and evaluated their antimicrobial, antioxidant, hemolytic, immunomodulatory and insulin-releasing properties. Their research demonstrates the extreme diversity of AMPs in amphibian skins and provides numerous templates for developing novel peptide antibiotics. Thus, we have yet another reason to protect biodiversity.

Xinwang Yang, Wen-Hui Lee, Yun Zhang. 2011. Extremely Abundant Antimicrobial Peptides Existed in the Skins of Nine Kinds of Chinese Odorous Frogs. Journal of Proteome Research, 2011: 111118134814004 DOI: 10.1021/pr200782u

Thursday, September 29, 2011

Australian Tree Frogs Collect Condensation for Hydration

Research published in the October issue of The American Naturalist shows that Australian green tree frogs survive the dry season with the help of the same phenomenon that fogs up eyeglasses in the winter.

Christopher R. Tracy and colleagues found the Australian Green Treefrog, Litoria caerulea, remain active during the dry season with apparently no available water and at temperatures that approach their lower critical temperature. The authors hypothesized that when the frogs retreated to their refugia condensation forms on their cold skin — just like it does on a eye glasses or the widows of your car.  They used frogs retrieved from natural dens and artificial dens and found the frogs absorb the condensing moisture through their skin, to maintain hydration during periods of little or no rain.

Before this study, the frogs' dry-season excursions were a bit mysterious.

"Every once in a while, we would find frogs sitting on a stick under the open sky, on nights when it was so cold they could barely move," said Dr. Chris Tracy, who led the research. "It was a real puzzle."

Tracy and his colleagues thought this behavior might enable the frogs collect condensation, but the hypothesis had never been tested.

The researchers designed a series of experiments using real frog dens in eucalyptus trees and artificial ones made from PVC pipe. They wanted to see if the frogs could collect enough moisture through condensation to compensate for what they lost being in the cold. They found that a cold night out cost a frog as much as .07 grams of water. However, a frog could gain nearly .4 grams, or nearly 1 percent of its total body weight, in water upon returning to the warm den.

The researchers also tested how well a frog's skin could absorb water, and found that as much as 60 percent of each water drop could be absorbed.

The results show that frogs can use condensation to hydrate themselves. And in a place as arid as the Australian savannahs during the dry season, where there is essentially no rain from June through August, every little bit counts.

"When there's no water available, even a small amount can mean the difference between surviving the dry season or not," Tracy said.

Christopher R. Tracy, Nathalie Laurence, Keith A. Christian, 2011, Condensation onto the Skin as a Means for Water Gain by Tree Frogs in Tropical Australia." The American Naturalist 178:553-558.(October 2011)

Tuesday, August 2, 2011

Amphibian Phylogeny Revised

Siren intermedia. JCM
Pyron and Weins have a new amphibian phylogeny that is now available on-line, prior to publication. No previous amphibian phylogeny used more than 522 species. However, other studies used limited taxon sampling and generated large numbers of partially overlapping sequence data for many species. The authors combine these data and produce a novel estimate of extant amphibian phylogeny, based on 2871 species (about 40% of living species) from 432 genera (85% of the 500 living genera). Species sampled averaged 2563 bp per species. The data set provides strong support for many groups recognized in previous studies, but it also suggests non-monophyly for several currently recognized families, particularly in hyloid frogs (e.g., Ceratophryidae, Cycloramphidae, Leptodactylidae, Strabomantidae). To correct these the authors provide a revised classification of extant amphibians for taxa traditionally delimited at the family and subfamily levels. The new phylogeny includes several new families, strongly supported by their data, but not recognized in current classifications (e.g., Alsodidae, Batrachylidae, Rhinodermatidae, Odontophrynidae, Telmatobiidae). Some highlights include the following. Within caecilians their results agree with other recent studies in supporting clades corresponding to Rhinatrematidae, Ichthyophiidae, and Caeciliidae, but the traditional family-level classification of caecilians that is used by Amphibia Web, (2011) was not supported by this study and they found the caeciliid subfamily Typhlonectinae to be paraphyletic. Within salamanders, the family and subfamily-level relationships were found to be  mostly consistent with most recent model-based molecular analyses and current classifications availabe on Amphibia Web and at Amphibian Species of the World web sites. However, they found strong support for a sister-group relationship between Sirenidae and all salamanders exclusive of Cryptobranchidae and Hynobiidae. Within frogs, the Hyloidea are several families were found not to be monophyletic: Ceratophryidae, Cycloramphidae, Leptodactylidae, and their solution is to recognizing several additional families relative to current classifications (Alsodidae, Batrachylidae, Odontophrynidae, Rhinodermatidae, Telmatobiidae) and synonymizing one (Strabomantidae with Craugastoridae). These newly recognized families are either re-definitions of previously recognized families (Rhinodermatidae,Telmatobiidae), or elevation of existing taxa presently below family rank (Alsodinae, Batrachylinae, Odontophrynini) to the rank of families. The study also provides evidence that the supermatrix approach provides an effective strategy for inferring large-scale phylogenies using the combined results of previous studies, despite many taxa having extensive missing data.

R. Alexander Pyron and John J. Wiens   2011. (in press) A large-scale phylogeny of Amphibia including over 2800 species, and a revised classification of extant frogs, salamanders, and caecilians. Molecular Phylogenetics and Evolution doi:10.1016/j.ympev.2011.06.012.

Friday, May 6, 2011

Species Accumulate Over Time - Amazonian Treefrog Assemblages

For more than two hundred years, the question of why there are more species in the tropics has been a biological enigma. A particularly perplexing aspect is why so many species live together in a small area in the tropics, especially at some sites in the rainforests of the Amazon Basin in South America.

New research on the evolution and ecology of treefrogs, published online in the journal Ecology Letters, sheds new light on the puzzle. The patterns found in treefrogs may also help to explain the high species richness of other groups of organisms -- such as trees, birds and insects -- in the Amazon rainforests.

"Treefrogs are a particularly important group to study for understanding amphibian diversity, because they can make up nearly half of all amphibian species in some rainforest sites," says lead author John J. Wiens, an Associate Professor in the Department of Ecology and Evolution at Stony Brook University. "Treefrogs also offer a striking example of the high local-scale biodiversity in the Amazon. At some sites in the Amazon rainforest, there are more treefrog species in a small area than there are across all of North America or Europe."

The researchers compiled data on the number of treefrog species at 123 sites around the world and analyzed the data with a new evolutionary tree (based on DNA sequence data) for 360 treefrog species. They discovered that the richness of treefrog species in the Amazon rainforest sites is not explained by wet, tropical climatic conditions alone.

"In fact, we found that many tropical rainforest sites that are outside the Amazon Basin have no more species than do some sites in temperate North America," explains Dr. Wiens.

Instead, the researchers discovered that the high biodiversity of Amazonian sites is related to different groups of treefrogs occurring together in the Amazon Basin for more than 60 million years -- since before most dinosaurs became extinct. In contrast, those sites in tropical rainforests that have relatively few treefrog species are in areas that were colonized by treefrogs much more recently.

These results also have important implications for humans. "The results suggest that the incredible biodiversity of amphibians in some sites in the Amazon Basin took more than 50 million years to develop," says Dr. Wiens. "If the Amazon rainforests are destroyed and the amphibian species are driven to extinction by human activities in the next few decades, it may take tens of millions of years for this incredible level of biodiversity to ever return.

John J. Wiens, R. Alexander Pyron, Daniel S. Moen. Phylogenetic origins of local-scale diversity patterns and the causes of Amazonian megadiversity. Ecology Letters, 2011; DOI: 10.1111/j.1461-0248.2011.01625.x

Monday, February 7, 2011

Frogs - Discovery and Extinction in Sri Lanka

New species of amphibians are being discovered at a remarkably rapid rate. AmphibiaWeb reports that during the past eight years 1336 new species of amphibians were described, that is one new amphibian species every 2.18 days for 8 years. We are only about 37 days into 2011 and 14 new species of amphibians have already been described (about one species every 2.7 days). In January 2010, an article in New Scientist reported the discovery of 30 new frog species in western Ecuador, 14 of which were found in a patch of cloud forest only a couple of miles wide. Needless to say most of the newly discovered amphibians are frogs, but the occasional new salamander or caecilian are found. 
Caption: The Sri Lankan Bush Frog, Pseudophilautus schmarda (Kelaart, 1854) is known only from the forested hill area of central Sri Lanka between 800 and  2300 feet above sea level. It can be found in low  vegetation and on the ground. JCM Natural History Photography.

However, despite the fact that new species are being discovered at a rapid rate, signs that amphibian species are disappearing due to human modifications of the environment are prevalent. Tthe Wildlife Heritage Trust of Sri Lanka conducted extensive surveys of the island’s amphibian fauna between 1993 and 2003 and discovered a large number of new species. An examination of the Natural History Museum (NHM- London) collection revealed about 140 specimens of frogs collected in Sri Lanka between 1850 and 1940. This was a time when rainforests were being cleared for tree planatations in the island's central mountains and southwestern wet zone. The wet forested habitat was reduced from about 16,000 km2 to about 750 km2. The NHM collection included 19 species of frogs (now placed in the genus Pseudophilautus) that have yet to be found on the island and are presumably extinct. Of particular interest was a frog Meegaskumbura et al. (2007) named Philautus maia (now Pseudophilautus maia), which appears to have carried its eggs attached to the abdomen, a behavior unknown in any other frogs. It has not been seen since 1876.

Now, Meegaskumbura and Aanamendra-Arachchi (2011) have described two, very small, new species of Sri Lankan shrub frogs in the genus Pseudophilautus. Pseudophilautus schneideri and Pseudophilautus hankeni, (22.8 mm and  21.9 mm SVL respectively). Pseudophilautus schneideri inhabits shrubs in open areas of the low to mid-elevations of the island’s southwestern wet zone that receive about 2 m per year, while P. hankeni  occurs on shrubs in the understorey of montane forests of the highest peaks ( 1,200–1,600 m elevation) of the Knuckles region. These two new frogs raise the total number of valid species of Sri Lankan Pseudophilautus to 67, 48 of which are extant and 19 are believed to extinct.  

Meegaskumbura, M. and K. Manamendra-Arachchi. 2011. Two new species of shrub frogs Rhacophoridae: Pseudophilautus) from Sri Lanka. Zootaxa 2747:1-18.
Meegaskumbura, M., K. Manamendra-Arachchi, C. J. Schneider, and  R. Pethiyagoda.  2007. New species amongst Sri Lanka’s extinct shrub frogs. Zootaxa, 1397, 1–15.