Thursday, November 27, 2014

Turtle relationships and their dispersal across the planet


The graphic abstract from Crawford et al. with photos added.
The question of what are turtles has been a source of a lively scientific debate over the past decades. Until recently, the phylogenetic placement of turtles within Amniota was uncertain and controversial. Molecular studies at the genome level confirm their sister relationship to archosaurs and rejected their relationship to lepidosaurs. However, relationships of lineages of turtles have not been studied using genomic techniques.

In a forthcoming paper in Molecular Phylogenetics and Evolution Crawford and colleagues (in press 2014) provide the first genome-scale analysis of turtle phylogeny. They sequenced 2381 ultraconserved element (UCE) loci representing a total of 1,718,154 bp of aligned sequence. The sampling includes 32 turtle taxa representing all 14 recognized turtle families and six additional outgroups.

This robust phylogeny shows that proposed phylogenetic names correspond to well-supported clades, and this topology is more consistent with the temporal appearance of clades and paleobiogeography.

The ultraconserved element (UCE) loci phylogeny supports the monophyly of Cryptodira, with Trionychia as the sister taxon to all other cryptodires. The clade including non-trionychian cryptodires was previously phylogenetically defined as ‘Durocryptodira’ by Danilov and Parham. The topology from ultraconserved elements and other molecular studies support the monophyly and the recognition of Durocryptodira, which is in contrast with the morphological hypothesis.

Combining the UCE phylogeny with the known fossil record of turtles allows reconstruction of some global biogeographic patterns. Intercontinental dispersal of turtles is common, usually involving a limited number of species.

The earliest fossils of stem testudinoids, stem trionychians, and stem cryptodires are from Eurasia. Mapping this onto the UCE phylogeny suggests cryptodires originated in the Jurassic of Eurasian. The emergence of cryptodires in Eurasia is complemented by the concurrent origin of pan-pleurodires in the Southern Hemisphere (Gondwana). Given the distribution of the clades and the timing of their origin, the geography of the cryptodire-pleurodire split can be plausibly linked to the breakup of the supercontinent Pangaea; a pattern common to other terrestrial vertebrates (e.g., placental vs. marsupial mammals).

Despite the Jurrasic origin of cryptodiran turtles they did not dominate the fauna of northern continents for 100 million years (in the Cenozoic). Instead, stem turtles mostly the Paracryptodira) were diverse and abundant in North America during the Cretaceous and into the Cenozoic. In the late Cretaceous cryptodires started to appear in North America invading via high latitude dispersal routes. The UCE phylogeny confirms one of the North American durocryptodire lineages, the Americhelydia, underwent a modest radiation and accounts for 38 living species.

Warm periods in the Paleogene are responsible for the dispersal of many organinsism into North America through high latitude dispersal routes, including a wave of testudinoids. Two are modest radiations, four species of Gopherus (Testudinidae); nine species of Rhinoclemmys (Geoemydidae). Previous studies suggested that these genera are sister taxa to all of the Old World members of their respective clades. The authors sequenced GopherusRhinoclemmys, and representative divergent members of geoemydids and testudinids and confirm the basal position of these North American genera. This pattern links the overall diversification at the base of these clades with their intercontinental dispersal, which can logically be attributed to periods of warm climate.

Similar to the Americhelydia, short branches within the testudinoids also suggest a rapid adaptive radiation that coincides with high latitude intercontinental dispersal events. This pattern suggests that global climate change has a major impact on the diversity and distribution of turtles.

The end of the Paleogene (45–23 Ma) coincides with global environmental changes, with the climate becoming significantly cooler and drier, thus much less favorable to turtles. Many turtle lineages that inhabited the Western Interior, including the last stem cryptodires in North America, became extinct at this time. One testudinoid lineage took advantage of the subtropical southeastern portions of the continent and radiated into the diverse clade Emydidae (53 species).

The recent description of a fossil taxon on the stem of Platysternon megacephalum from the Eocene of North America raises possibility that the more inclusive Emysternia may also have an American origin. Depending on the resolution of that possibility, the UCE topology indicates that two dispersal events into North America led to the origin of 36–43% of the recognized families of turtles.

The entire article is available on-line.

Citation
Crawford NG, Parham JF, Sellas AB, Faircloth BC, Glenn TC, Papenfuss TJ, Henderson JB, Hansen MH, and Simison WB. 2014 (2015). A phylogenomic analysis of turtles. Molecular Phylogenetics and Evolution (2014).



Saturday, November 22, 2014

A large sea snake harvest that has gone unnoticed for a decade

Conservation of sea snakes is virtually nonexistent in Asia, and its role in human–snake interactions in terms of catch, trade, and snakebites as an occupational hazard is mostly unexplored. In a recent paper in Biological Conservation Nyguen et al (2014) report data on sea snake landings from the Gulf of Thailand, a hotspot for sea snake harvest by squid fishers operating out of the ports of Song Doc and Khanh Hoi, Ca Mau Province, Vietnam. The information was collected during documentation of the steps of the trading process and through interviewers with participants in the trade. Squid vessels return to their ports once per lunar synodic cycle and fishers sell snakes to merchants who sort, package, and ship the snakes to various destinations in Vietnam and China for human consumption. They are also used as a source of traditional remedies. Annually, 82 tons, roughly equal to 225,500 individual snakes, of live sea snakes are brought to ports. Knowledge of the harvest has been largely ignored and the rate of harvest constitutes one of the largest venomous snake and marine reptile harvest activities in the world today. In the harvest two species, Lapemis curtus and Hydrophis cyanocinctus, constituted about 85% of the snake biomass, and Acalyptophis peronii, Aipysurus eydouxii, Hydrophis atriceps, H. belcheri, H. lamberti, and H. ornatus made up the remainder. The results of this new paper establish a quantitative baseline for characteristics of catch, trade, and uses of sea snakes. Other key observations include the timing of the trade to the lunar cycle, a decline of sea snakes harvested over the study period (approximately 30% decline in mass over 4 years), and the treatment of sea snake bites with rhinoceros horn. Emerging markets in Southeast Asia drive the harvest of venomous sea snakes in the Gulf of Thailand and sea snake bites present a potentially lethal occupational hazard.

The authors suggest that the Gulf of Thailand/southern Vietnam is one of the largest harvests of venomous snake and marine reptiles in the world. Yet sea snakes are not even mentioned in studies concerning reptile exploitation in Asia or globally. This underreported status is particularly notable given that the Indonesian archipelago has the highest marine species diversity in general and specifically is among the areas ranked as having the greatest richness of sea snake species on Earth. Still, in this area an unexplained decline of sea snakes has been reported. The eight commercially traded sea snake species reported on represent a significant proportion of the 20 species known in the Gulf of Thailand and of the 25 species known from Vietnam, including the South China Sea.
Globally, 9% of sea snakes are threatened, 6% are near threatened, and 34% are data deficient, as defined by the International Union for the Conservation of Nature (IUCN). The species in this study, as well as all other species known from the Gulf of Thailand, are currently categorized as either least concern or data deficient. However, the results suggest that in the Gulf of Thailand a large subset of the sea snake species now considered as least concern or data deficient may, in fact, be in danger of having their populations damaged or destroyed through over harvesting. According to the results presented in this paper, the number of sea snakes harvested from the Gulf of Thailand by boats based at the study sites was 6.35 specimens per square kilometer per year. The authors could not exclude the possibility that sea snake species in addition to those observed were traded from other harvesting grounds (e.g., harvest landing in Vung Tau, Vietnam). The volume of harvested sea snakes documented is a conservative estimate of the total harvest from the Gulf of Thailand. It is very likely that more snakes were harvested by squid vessels and trawlers that originated from ports in Malaysia and Thailand. Sea snakes have been brought into the ports of Songkhla, Thailand, Kra Isthmus, Thailand, and Endau, Malaysia. Sea snake harvests similar to the one reported here could be occurring in (or spread to) other areas of the South China Sea and wider Southeast Asia. Ten years ago in Quảng Ng˜ai, the sea snake bycatch was discarded due to fear of bites and a lack of market; however, in 2011 their price was US$10–35/kg. Knowledge of the biology of sea snakes and their role in the ecosystem is limited. Thus, understanding of the effect that this harvest may have on populations or on the wider ecosystem is limited. The results supply evidence that the mass of snakes harvested from the Gulf of Thailand has been decreasing since 2009, and fishers interviewed consistently reported a decline since they first began capturing sea snakes as a commodity.

Snake bites during the trade process are occupational hazards that carry a high risk given the lethal venoms and lack of availability of antivenin therapy. The economic incentive of harvesting sea snakes, from the fishers’ and merchants’ perspectives, clearly outweighs the snake bite risk. With respect to fatalities the authors report, one affected family continued trading in sea snakes, while another family terminated participation in the snake trade.

The authenticity and effectiveness of rhinoceros horn and other locally used remedies for snake bites remains unproven. Yet, use of rhinoceros body parts in Vietnam has been directly linked to poaching of rhinoceros in South Africa. The observation suggests a link between rhinoceros poaching and sea snake harvest in the Gulf of Thailand. Both fishers and merchants take advantage of emerging market opportunities. According to the merchants, government, and nongovernmental officials interviewed, the large-scale harvest of sea snakes from the Gulf of Thailand is tied to economic prosperity and thus increase demand domestically in Vietnam and from China for snake products. The demand is due to the perceived health benefits of sea snakes and consumption of sea snakes as status
Items. This particular sea snake harvest has been going on essentially unnoticed by national and international conservation organizations for more than a decade, in part because it apparently does not overtly conflict with Vietnamese laws. Yet, given the volume of snakes and the wide spectrum of species extracted and that the environmental effects of the harvest are unknown, immediate attention by conservation organizations to sea snake harvesting appears warranted. Ironically, the enforcement of laws aimed at managing the trade in widely harvested terrestrial snakes, such as various cobra species (e.g., Naja spp., Ophiophagus hannah), may have the unintended consequence of increasing the market for sea snakes.

Citation

Nguyen C, Nguyen TT, Moore A, Montoya A, Rasmussen AR Broad K, Voris HK, Takacs Z. 2014. Sea Snake Harvest in the Gulf of Thailand. Conservation Biology 28: 1677-1687.

Monday, November 17, 2014

A new Chironius from Bahia, Brazil

Chironius diamantine. Photo credit: R. Santos
The Neotropical colubrid genus Chironius contains a monophyletic assemblage of snakes having very low (10 or 12) dorsal scale rows at midbody. Currently the genus includes 20 species of diurnal snakes distributed from Honduras south to Uruguay and northeastern Argentina. Recently, a lectotype was designated for Chironius flavolineatus, a widespread species in open formations of South America (particularly in the Cerrado and Caatinga), with records from Marajó island, northern Brazil. Chironius flavolineatus is distinguishable from other members of the genus by the presence of a conspicuous yellow vertebral stripe bordered anteriorly by black. In a new Zootaxa paper, Fernandes and Hamdan (2014) describe the 21st species of Chironius, C. diamantine which differs from other Chironius in the combination of its color pattern, 2-4 temporal scales, an entire anal plate, 6-10 rows of dorsal scales at midbody, and some other characters. The new species is known from municipalities of Morro do Chapéu, Rio de Contas, and Palmeiras in the Chapada Diamantina, Bahia, Brazil. All specimens were found between sea level 1000 m asl. One individual was observed foraging about 3:00 PM on the banks of a rocky river near a waterfall, a few minutes later plunged into the river and remained there for about two minutes.

Citation

Fernandes DS, & Hamdan B. 2014. A new species of Chironius Fitzinger, 1826 from the state of Bahia, Northeastern Brazil (Serpentes: Colubridae). Zootaxa, 3881(6), 563-575.

Sunday, November 16, 2014

Relationships between some Old World Rat Snakes resolved

These snakes should all be placed in 
the genus Gonyosoma
The Old World Rat Snakes have been a source of confusion for many years, they have a diverse morphology and behaviors that have been a puzzle to herpetologists for some time - the kind of puzzle best solved with molecular techniques. The last decade has seen an incredible rise in the use of molecular phylogenies to examine relationships in snakes, assess biogeographic origins, understand processes of adaptive radiation and ultimately correct taxonomy with regard to paraphyletic and polyphyletic groups at multiple levels. The importance of using phylogenetic trees to uncover genealogical relationships and properly construct a taxonomy of organisms cannot be overstated. The development of DNA sequencing technology has increased the available genetic data for phylogenetic inference and the development of model-based statistical methods, such as maximum likelihood and Bayesian inference, which has enhanced the reliability of reconstructed phylogenies. Using molecular data to examine phylogenetic relationships provides evidence to clarify systematic ambiguities from morphological characters and helps avoid misleading relationships due to convergence of morphology. Therefore, an abundance of molecular data with information from independent loci is able to provide strong evidence to assess taxonomic composition and test monophyly.

Using one mitochondrial gene and five nuclear loci, Xin Chen and colleagues (2014) evaluated the taxonomic status of a rare Borneo endemic, the Rainbow Tree Snake Gonyophis margaritatus. The authors inferred a molecular phylogeny of 101 snake species. Both maximum likelihood and time- calibrated Bayesian inference phylogenies demonstrated that G. margaritatus is sister to the Green Trinket Snake, Rhadinophis prasinus of northern Thailand, previously considered to be part of a radiation of Old World ratsnakes. This group is in turn sister to a group containing Rhadinophis frenatus (India, southern China, Taiwan, and North Vietnam) and the Rhinoceros Ratsnake, Rhynchophis boulengeri with the entire clade originating in the mid-Miocene (~16 Ma) in Southeast Asia. This group is sister to the genus Gonyosoma and together originated in the early Miocene (~20 Ma). The authors discuss three potential solutions towards eliminating polyphyly of the genus Rhadinophis, but recommend using the genus name Gonyosoma for all species within this clade, which currently contains all of the species within the genera Gonyosoma, Gonyophis, Rhadinophis, and Rhynchophis.

Citation
Chen X, McKelvy AD, Grismer L, Matsui M, Nishikawa K, & Burbrink FT. 2014. The phylogenetic position and taxonomic status of the Rainbow Tree Snake Gonyophis margaritatus (Peters, 1871) (Squamata: Colubridae). Zootaxa, 3881, 532-548.


Friday, November 7, 2014

Origin of the ventilatory apparatus of turtles

A Computed Tomography rendering of a snapping turtle 
(Chelydra serpentina) showing the skeleton (white), lungs 
(blue), and abdominal muscles (red and pink) used to ventilate 
the lungs. Because turtles have locked their ribs up into the
 iconic turtle shell, they can no longer use their ribs to breathe as 
in most other animals and instead have developed a 
unique abdominal muscle based system. 
Photo credit: Emma R. Schachner.
Through the careful study of modern and early fossil tortoise, researchers now have a better understanding of how tortoises breathe and the evolutionary processes that helped shape their unique breathing apparatus and tortoise shell. The findings published in a paper, titled: Origin of the unique ventilatory apparatus of turtles, in the scientific journal, Nature Communications, on Friday, 7 November 2014, help determine when and how the unique breathing apparatus of tortoises evolved.

Lead author Dr Tyler Lyson of Wits University's Evolutionary Studies Institute, the Smithsonian Institution and the Denver Museum of Nature and Science said: "Tortoises have a bizarre body plan and one of the more puzzling aspects to this body plan is the fact that tortoises have locked their ribs up into the iconic tortoise shell. No other animal does this and the likely reason is that ribs play such an important role in breathing in most animals including mammals, birds, crocodilians, and lizards."

Instead tortoises have developed a unique abdominal muscular sling that wraps around their lungs and organs to help them breathe. When and how this mechanism evolved has been unknown.

"It seemed pretty clear that the tortoise shell and breathing mechanism evolved in tandem, but which happened first? It's a bit of the chicken or the egg causality dilemma," Lyson said. By studying the anatomy and thin sections (also known as histology), Lyson and his colleagues have shown that the modern tortoise breathing apparatus was already in place in the earliest fossil tortoise, an animal known as Eunotosaurus africanus.

This animal lived in South Africa 260 million years ago and shares many unique features with modern day tortoises, but lacked a shell. A recognizable tortoise shell does not appear for another 50 million years.

Lyson said Eunotosaurus bridges the morphological gap between the early reptile body plan and the highly modified body plan of living tortoises, making it the Archaeopteryx of turtles.
"Named in 1892, Eunotosaurus is one of the earliest tortoise ancestors and is known from early rocks near Beaufort West," said Professor Bruce Rubidge, Director of the Evolutionary Studies Institute at Wits University and co-author of the paper.

"There are some 50 specimen of Eunotosaurus. The rocks of the Karoo are remarkable in the diversity of fossils of early tortoises they have produced. The fact that we find Eunotosaurus at the base of the Karoo succession strongly suggest that there are more ancestral forms of tortoises still to be discovered in the Karoo," Rubidge added.

The study suggests that early in the evolution of the tortoise body plan a gradual increase in body wall rigidity produced a division of function between the ribs and abdominal respiratory muscles. As the ribs broadened and stiffened the torso, they became less effective for breathing which caused the abdominal muscles to become specialized for breathing, which in turn freed up the ribs to eventually -- approximately 50 million years later -- to become fully integrated into the characteristic tortoise shell.

Lyson and his colleagues now plan to investigate reasons why the ribs of early tortoises starting to broaden in the first place. "Broadened ribs are the first step in the general increase in body wall rigidity of early basal tortoises, which ultimately leads to both the evolution of the tortoise shell and this unique way of breathing. We plan to study this key aspect to get a better understanding why the ribs started to broaden."

Citation

Lyson TR, Schachner  ER, Botha-Brink J, Scheyer TM, Lambertz M, Bever GS, Rubidge, BS de Queiroz K. Origin of the unique ventilatory apparatus of turtles. Nature Communications, 2014; 5: 5211 DOI: 10.1038/ncomms6211

Thursday, November 6, 2014

External genitalia in amniote evolution

When it comes to genitalia, nature enjoys variety. Snakes and lizards have two. Birds and people have one. And while the former group's paired structures are located somewhat at the level of the limbs, ours, and the birds', appear a bit further down. In fact, snake and lizard genitalia are derived from tissue that gives rise to hind legs, while mammalian genitalia are derived from the tail bud. But despite such noteworthy contrasts, these structures are functionally analogous and express similar genes.

How do these equivalent structures arise from different starting tissues?

This is a python embryo at 11 days after 
oviposition (egglaying). The right hemipenis
(genitalia) bud and vestigial limb-bud can be 
seen near the tail end of the embryo, in the 
center of the tail 'spiral'. (two white 'blobs'). 
Photo Credit: Patrick Tschopp.
Reporting in Nature, researchers in Harvard Medical School's Department of Genetics, led by departmental chair Clifford Tabin, have found that the answer is not unlike the real estate axiom Location, location, location.

The embryonic cloaca -- which eventually develops into the urinary and gut tracts -- issues molecular signals that tell neighboring cells and tissues to form into external genitalia. The cloaca's location determines which tissues receive the signal first. In snakes and lizards, the cloaca is located closer to the lateral plate mesoderm, the same tissue that makes the paired limbs, receives the signal. In mammals, the cloaca is closer to the tail bud.

To further confirm this finding, the researchers grafted cloaca tissue next to the limb buds in one group of chicken embryos, and beside the tail buds in a second group. They found that in both cases, cells closer to the grafted cloaca responded to the signals and partially converted toward a genitalia fate.

This proves that different populations of cells with progenitor potential are able to respond to cloaca signaling and contribute to genitalia outgrowth.

"While mammal and reptile genitalia are not homologous in that they are derived from different tissue, they do share a 'deep homology' in that they are derived from the same genetic program and induced by the same ancestral set of molecular signals," said Tabin, who is also the George Jacob and Jacqueline Hazel Leder Professor of Genetics.

"Here we see that an evolutionary shift in the source of a signal can result in a situation where functionally analogous structures are carved out of nonhomologous substrate," said Patrick Tschopp, an HMS research fellow in genetics in Tabin's lab and first author on the paper. "Moreover, this might help to explain why limbs and genitalia use such similar gene regulatory programs during development."

Citation

Tschopp P, Sherratt E, Sanger TJ, Groner AC, Aspiras AC, Hu JK, Pourquié O, Gros J, Tabin CJ. A relative shift in cloacal location repositions external genitalia in amniote evolution. Nature, 2014; DOI: 10.1038/nature13819

An amphibious ichthyosaur

Fossil remains show the first amphibious ichthyosaur found in China by a team led by a UC 
Davis scientist. Its amphibious characteristics include large flippers and flexible wrists, essential 
for crawling on the ground. Photo Credit: Ryosuke Motani/UC Davis
The first fossil of an amphibious ichthyosaur has been discovered in China by a team led by researchers at the University of California, Davis. The discovery is the first to link the dolphin-like ichthyosaur to its terrestrial ancestors, filling a gap in the fossil record. The fossil is described in a paper published in advance online Nov. 5 in the journal Nature.

The fossil represents a missing stage in the evolution of ichthyosaurs, marine reptiles from the Age of Dinosaurs about 250 million years ago. Until now, there were no fossils marking their transition from land to sea.

"But now we have this fossil showing the transition," said lead author Ryosuke Motani, a professor in the UC Davis Department of Earth and Planetary Sciences. "There's nothing that prevents it from coming onto land."

Motani and his colleagues discovered the fossil in China's Anhui Province. About 248 million years old, it is from the Triassic period and measures roughly 1.5 feet long.

Unlike ichthyosaurs fully adapted to life at sea, this one had unusually large, flexible flippers that likely allowed for seal-like movement on land. It had flexible wrists, which are essential for crawling on the ground. Most ichthyosaurs have long, beak-like snouts, but the amphibious fossil shows a nose as short as that of land reptiles.

Its body also contains thicker bones than previously-described ichthyosaurs. This is in keeping with the idea that most marine reptiles who transitioned from land first became heavier, for example with thicker bones, in order to swim through rough coastal waves before entering the deep sea.

The study's implications go beyond evolutionary theory, Motani said. This animal lived about 4 million years after the worst mass extinction in Earth's history, 252 million years ago. Scientists have wondered how long it took for animals and plants to recover after such destruction, particularly since the extinction was associated with global warming.

"This was analogous to what might happen if the world gets warmer and warmer," Motani said. "How long did it take before the globe was good enough for predators like this to reappear? In that world, many things became extinct, but it started something new. These reptiles came out during this recovery."

Citation

Motani R., Jiang D-Y, Chen G-B, Tintori A, Rieppel O, Ji C, Huang J-D. 2014. A basal ichthyosauriform with a short snout from the Lower Triassic of China. Nature, 2014; DOI: 10.1038/nature13866

Wednesday, November 5, 2014

Snakebite in rural Nepal, diagnosis of species responsible

Photo credit; DA Warrell
Starting with a simple DNA swab taken from fang marks on people bitten by snakes, an international research team correctly identified the species of the biting snake 100 percent of the time in a first-of-its-kind clinical study, according to data presented today at the American Society of Tropical Medicine and Hygiene's (ASTMH) Annual Meeting.
The study, conducted at three medical facilities in Nepal, found that if snake DNA could be isolated from the bite wound, the test identified the species of snake responsible every time.
"These findings represent a significant step toward improving care for patients in areas of the world where snakebites constitute a massive but neglected health risk," said François Chappuis, MD, PhD, chief of the division of tropical and humanitarian medicine at Geneva University Hospitals, Switzerland, who directed the study and presented the results. "This DNA test may hasten more effective bedside diagnostics for snakebite victims, giving them a better chance of surviving and making a full recovery."
Bites from venomous snakes are common in many parts of the world and an especially serious unresolved health problem to millions of people living in South and Southeast Asia, as well as Africa and Latin America. Although there are no reliable numbers at the global scale, a study published in 2008 estimated at least 421,000 cases of envenomation and up to 94,000 deaths occur worldwide from snakebite each year. However, experts warn that these figures may underestimate the real problem, which is believed to affect several million people bitten by venomous snakes annually and hundreds of thousands who die or survive disabled, suffering from amputation or deformed limbs as a result of unavailable or delayed treatment.
In some villages of the study area of southeast Nepal reported today, a community-based survey in 2002 revealed an estimated 1,162 snakebites and 162 snakebite deaths per 100,000 people per year, one of the highest rates ever reported. Likewise, a recent survey of more than one million deaths in India, published in the journal PLoS Neglected Tropical Diseases in 2011, found that 46,000 people die every year in India from snakebites. This figure is about 20 times the official death toll recorded in Indian hospitals, most likely because less than one in four fatal snakebite cases had received any hospital treatment, the study revealed.
"People bitten by snakes in South Asia often do not seek treatment at a medical facility, and if they do, the vast majority don't take the snake to clinics, although it is often killed, and can't identify the species that bit them," Chappuis said. "Yet knowing the species of snake is critical to determining the best course of treatment."
In Nepal, for example, cobras and kraits are among the most common venomous snakes. Their venoms attack the nervous system and can be fatal. Patients bitten by either snake have similar symptoms, such as nausea, headache, drowsiness and limb as well as respiratory paralysis. However, the toxins of these snakes and their mechanisms of action differ, and so does the response to antivenom and other drugs. For example, the locally available antivenom has limited or no efficacy against krait envenomation, which often leads to useless repeated doses resulting in increased cost and--possibly--adverse side effects, explained Chappuis. Also, bites by cobras and kraits lead to different complications that the attending physicians need to prevent or be prepared for. Therefore, positive identification of the biting species becomes important to effective treatment.
Preliminary results presented today show that among 194 bite-site DNA samples collected in Nepal during the study, 87 were from a venomous species. The spectacled cobra accounted for 42 bites and the common krait for 22. In 21 cases, the patients brought the dead snake with them, and in those cases expert examination of the snake and the DNA test, performed by different investigators, independently provided the correct identification. Snake DNA could be obtained from about one in four bite wounds. According to the researchers, one factor that excluded samples was if the patient attempted folk or home remedies tampering with the bite site prior to arriving at the medical clinic.
The research team also correlated clinical symptoms with the species biting patients. They found that krait bites happened more often at night, indoors, or while people were sleeping, while cobra or pitviper bites were more likely to cause swelling at the bite site. The technique also identified several species of non-venomous snake involved in bites.
"The proportion of non-venomous snakes that bite people is actually rather high," said Ulrich Kuch, PhD, of the department of tropical medicine and public health in the Institute of Occupational, Social and Environmental Medicine of Goethe University (Frankfurt, Germany), and developer of the snake DNA identification test. "Snakebite patients are kept in the hospital for 24-hour observation, which strains healthcare resources in many countries. By identifying species of nonvenomous snake, it is also possible to assist the local people and avoid hospital stays for those not at risk of envenomation."
The research team is currently developing a rapid diagnostic "dip-stick" test similar to a pregnancy test that could be used to rule out certain common venomous snakes and help physicians more quickly decide the best course of treatment. Conversely, if for example, krait venom is detected, doctors could quickly give antivenom instead of waiting for clinical signs of envenomation, as is current practice. They would also accelerate the transfer of patients to referral hospitals with intensive care units able to ensure adequate respiratory support. Such a test would be easy to administer in rural healthcare settings with limited resources, said Chappuis.
"That's where the recently developed DNA test could be most valuable," he added. While the DNA test is labor intensive and time consuming, making it impractical for day-to-day clinical use, its high accuracy could allow it to become a "gold standard" in clinical studies of rapid diagnostic tests under development. In addition, the DNA test could become a powerful epidemiological tool to determine which species of snake bite people in various tropical regions.
"Knowing the distribution of snakes and the number of snakebites within a region could help improve allocation of scarce antivenoms to areas where they are most needed" said Chappuis.
The researchers have completed small clinical studies in Nepal and Bangladesh and are preparing a larger multi-center clinical study using the DNA test in Myanmar and Nepal, countries with among the highest rates of snakebite deaths. The current study is funded by the UBS Optimus Foundation and the Swiss National Fund.
"We need new tools in order to save more lives," said Sanjib K. Sharma, MD, professor of medicine at the B.P. Koirala Institute of Health Sciences in Nepal, and the principal investigator of the study. "There is gross disparity in the management and outcome of snakebites since most occur in rural, agricultural areas while the great majority of healthcare workers are in urban locations."
"Most people are unaware that snakebite is a very real and serious threat both to the health and economic vitality of rural communities throughout much of the developing world," said Alan J. Magill, MD, FASTMH, president of the American Society of Tropical Medicine and Hygiene. "This innovative research may be enabling for the development of a point of care test to positively identify biting snakes. Accurate diagnosis would go a long way toward documenting the impact of snakebite and improving medical care for this often neglected yet pervasive problem."

Citation
Sharma SK, Kuch U, Höde P, Bruhse L. Pandey D, Chappuis F, Alirol E. 2014. Use of clinical predictors and molecular diagnosis to identify the species responsible for snakebite in rural Nepal. AmericanSociety of Tropical Medicine and Hygiene (Burness Communications). Abstract. ASTMH 63rd Annual Meeting Nov. 2-6. New Orleans.

Sunday, November 2, 2014

Frogs make their offspring grow at a faster rate

Breeding male of Rana arvalis from the study area. 
Photo Credit: Germán Orizaola.
Gobal warming is altering the reproduction of plants and animals, notably accelerating the date when reproduction and other life processes occur. A study by the University of Uppsala (Sweden), including the participation of Spanish researcher Germán Orizaola, has discovered that some amphibians are capable of making their offspring grow at a faster rate if they have been born later due to the climate.

Over recent decades many organisms, both plants and animals, have experienced a notable advance in the date when many of their life processes (like reproduction, migration or flowering) occur, attributed to the impact of climate change. An article published in the journal Ecology examines the effects that these changes in the reproduction date have on the life cycles of the amphibians.
"We specifically examined whether changes in the reproduction date of a common amphibian species in the north of Europe, Rana arvalis, can condition the growth and development of their offspring," the Spanish researcher Germán Orizaola, from the University of Uppsala (Sweden) and co-author of the study, said.

Results revealed that female frogs have the ability to influence both the growth rate and the development of their offspring, and they adjust it depending on the date of reproduction.
According to Orizaola, "the mechanism by which the female frogs can condition the growth of their larvae could be due to the genes associated with the maintenance of their biological clock being transferred to the embryos and becoming active even before fertilization. This would provide the larvae with the exact information regarding the progression of the growing season."

One of the characteristics associated with climate change is an increase in the inter-annual variability of climatic conditions, so organisms are also exposed to greater uncertainty when it comes to determining the right time to reproduce. This explains why the existence of mechanisms adjusting growth and development rates depending on the variation in the start of breeding is highly advantageous for many species.

In particular, as part of this study they observed that by delaying the date of reproduction (which simulated a time of environmental instability), the result was an equivalent reduction in the growth period for the larvae. "That means the later this species of frog breeds, the faster the larvae develop," explains the scientist.

An interesting aspect of the study is that the acceleration in growth is produced under constant lab conditions. "The larvae were not exposed to any outside sign that would indicate the progression of the growing season," adds Orizaola.

"This result is very novel and demonstrates that the acceleration in the development of the larvae is conditioned by the breeding females, which reveals the existence of a 'transgenerational effect' in which the breeding adults are capable of altering key aspects of the life cycle for the following generations, to better prepare them to survive the environmental conditions that they are going to experience," concludes the expert.

Citation
Richter-Boix A, Orizaola G, Laurila A. 2014 Transgenerational phenotypic plasticity links breeding phenology with offspring life-history. Ecology, 2014; 95 (10): 2715 DOI: 10.1890/13-1996.1