Tag Archives: #amphibians

The World’s Largest Animal Genome (Biology)

The Australian lungfish replaces the Mexican axolotl as holding the record for the “largest genome in the animal kingdom”. Its genome shows the evolutionary innovations that made living on land possible.

380 million years ago, the first fish began to conquer land. The Australian lungfish – an endangered air-breathing species – is one of the few living relatives of these first “land fish”.

An international research team has now used the latest DNA sequencing technologies to decode the huge genome of this fish species for the first time. The analysis has been published in the journal Nature. It gives new insights into the evolutionary innovations that enabled fish to live on land.

The study was a team effort of researchers from Hamburg, Constance, Vienna, Lyon and Würzburg. Senior Professor Manfred Schartl from the Biocentre of Julius-Maximilians-Universität (JMU) Würzburg in Bavaria, Germany, an expert in the biology and evolution of fish, was an important contributor to the study as was his postdoc Kang Du and Susanne Kneitz, a bioinformatician from the JMU Chair of Biochemistry and Cell Biology.

Genome is 14 times larger than that of humans

According to the study, the lungfish genome is the largest animal genome ever sequenced. Boasting 43 billion base pairs, it is 14 times larger than the human genome, exceeding the genome of the axolotl, the previous record holder in the animal kingdom, by an impressive 30 percent.

So why is the genome so large? Astonishingly, the lungfish does not have many more genes than other vertebrates. But it does have more mobile genetic elements, so-called transposable elements. “These elements can be consider as a kind of computer virus. They multiply on their own but don’t have a function. As a scientist you wonder why the ‘genetic hard drive’ of the lungfish has not crashed long ago given the high number of transposable elements,” says Manfred Schartl.

Fins similar to human limbs

The Australian lung fish (Neoceratodus forsteri) lives in slow flowing rivers and bodies of standing water. Due to its newt-like physique, it was incorrectly assumed to be part of the amphibians in the 19th century. Today we know that as a lungfish it belongs to an archaic group of aquatic creatures from which all terrestrial vertebrates developed.

The “fleshy” fins of the lungfish possess an anatomical bone arrangement which looks already similar to that of human limbs. This allows the Australian lungfish to move like salamanders in water and on land. Moreover, they have lungs which allow them to breathe air above water so as not to drown. And they are capable of detecting airborne smells.

Closer to amphibians than to fish

The genome analysis reveals striking similarities between the Australian lungfish and terrestrial vertebrates. For example, the number and the spatial and temporal expression patterns of genes that are associated with the development of lungs, jointed limbs and with the detection of airborne smells are much more similar to amphibians and other land vertebrates than their fish relatives.

So far, scientists have debated controversially whether lungfish or the equally archaic coelacanths are more closely related to terrestrial vertebrates The study in Nature now shows that the lungfish are genetically closer to land animals and humans: 420 million ago, they split off from the coelacanths and formed a lineage leading to land animals.


Since 2018, the German Research Foundation (DFG) has funded the sequencing of the lungfish genome by JMU Professor Manfred Schartl, Professor Torsten Burmester (University of Hamburg) and Professor Axel Meyer (University of Constance) with more than EUR 500,000.

Featured image: The bone arrangement in the fins of the Australian lungfish is very similar to that in humans limbs. (Image: Uni Konstanz / Pixabay)


Axel Meyer, Siegfried Schloissnig, Paolo Franchini, Kang Du, Joost Woltering, Iker Irisarri, Wai Yee Wong, Sergej Nowoshilow, Susanne Kneitz, Akane Kawaguchi, Andrej Fabrizius, Peiwen Xiong, Corentin Dechaud, Herman Spaink, Jean-Nicolas Volff, Oleg Simakov, Thorsten Burmester, Elly Tanaka, Manfred Schartl: “Giant Lungfish genome elucidates the conquest of land by vertebrates”. Nature, 18 January 2021. DOI: 10.1038/s41586-021-03198-8

Provided by University of Wruzburg

In the Cerrado, Topography Explains the Genetic Diversity of Amphibians More Than Land Cover (Biology)

Study shows that a tree frog endemic to a mountainous region of the Brazilian savanna is unable to disperse and find genetically closer mates when the terrain is rugged, potentially endangering survival of the species.

The savanna tree frog Bokermannohyla ibitiguara is about 4 cm long and is found only in gallery forest along streams in the Serra da Canastra mountain range in the state of Minas Gerais, Southeast Brazil. In this watery forest environment, it can grow, feed, mate, and lay eggs without needing to range very far throughout its life cycle, according to a study published in Diversity and Distributions.

Study shows that a tree frog endemic to a mountainous region of the Brazilian savanna is unable to disperse and find genetically closer mates when the terrain is rugged, potentially endangering survival of the species. ©Renato C. Nali

According to the Brazilian and US researchers who conducted the study, topography rather than vegetation is the main factor leading to more or less dispersal of the species in the territory, and this information is even recorded in its DNA.

They analyzed genetic variation among groups of B. ibitiguara living inside and outside the Serra da Canastra National Park, a protected area in the region, discovering that the flatter the terrain, the more genetically diverse is the population.

In areas of highly variable elevation, individuals are genetically similar. In evolutionary terms, this can be harmful to the species, which becomes more susceptible to disease and climate change, for example.

“Genetic analysis and conservation studies typically take land cover into account, among other factors, but the Cerrado [Brazilian savanna] is topographically diverse, including montane regions with high plateaus [chapadões] separated by low areas. We set out to verify whether this variable terrain played a part in the genetic diversity of the species, and found that it did. The vegetation alone didn’t explain the genetic differences we identified between sites, or even within the same site. The topography did,” said Renato Christensen Nali, first author of the article and a professor at the Federal University of Juiz de Fora’s Institute of Biological Sciences (ICB-UFJF) in Minas Gerais, Brazil.

The study was one of the results of Nali’s doctoral research, conducted at São Paulo State University’s Bioscience Institute (IB-UNESP) in Rio Claro, Brazil, with a scholarship from FAPESP (São Paulo Research Foundation).

The research was part of the project “Reproductive ecology of anuran amphibians: an evolutionary perspective”, for which the principal investigator is Cynthia Peralta de Almeida Prado, a co-author of the article. She is a professor at UNESP’s School of Agrarian and Veterinary Sciences in Jaboticabal and teaches graduate students in zoology at IB-UNESP in Rio Claro.

The flatter the better

“The findings are very interesting because they bring to light a novel factor for conservation of the Cerrado, among other reasons. Ecological corridors and native forests are rightly considered important for conservation units, but more attention needs to be paid to the type of terrain. The topography should permit dispersal of the animals,” said Nali, who heads ICB-UFJF’s Amphibian Evolutionary Ecology Laboratory (Lecean).

To arrive at the results, the researchers analyzed 12 populations of B. ibitiguara, six inside Serra da Canastra National Park and six outside. Genetic diversity was much higher among the anurans living in the protected area than among those living outside the park. When the researchers correlated information on the degree of protection of the areas with the state of the vegetation, they found that these factors were less decisive for genetic diversity than the topography.

“The terrain is much more rugged outside the park, whereas inside it there’s a large, very even plateau where the anurans can disperse more, find mates in more distant areas, and increase their genetic diversity,” Nali said. “Outside the park, the rugged terrain and variable elevation appear to confine them to small areas.”

The influence of these factors was evidenced by genetic tests. The researchers used a technique known as macrosatellite marker analysis to examine specific regions of the genome and found higher allele diversity in the populations living in the park. Allele diversity is one of the determinants of genetic integrity and adaptive potential.

In addition, the populations living outside the park displayed a greater loss of heterozygosity. If this loss, which is associated with declining genetic variability, recurs across several generations, it can eventually threaten the population’s survival.

The study underscores the importance of topography as a factor to consider in conservation studies, as well as showing how the mere presence of a species in an area cannot ensure that it is not endangered.

“Molecular analysis enables us to find out if a population’s genetic status is favorable,” Nali said. “An area may have a large number of individuals, but DNA analysis may show that its genetic constitution is unfavorable, with few alleles and low heterozygosity. In practice, therefore, the population’s effective size is small.”

Although the study focused on only one species, he added, the findings can apply to others as well since the physical characteristics associated with dispersal are similar for other frogs and toads. More species need to be investigated to confirm the applicability of the findings.

The group noted that land cover nevertheless remains an important factor for conservation in the Cerrado, more than 50% of which has been converted into pasture or cropland, while less than 5% is protected by conservation units.

References: Nali, RC, Becker, CG, Zamudio, KR, Prado, CPA. Topography, more than land cover, explains genetic diversity in a Neotropical savanna tree frog. Divers Distrib. 2020; 26: 1798– 1812. https://doi.org/10.1111/ddi.13154

Provided by São Paulo Research Foundation (FAPESP)

How Do Some Frogs ‘Rebound’ After Disease While Others Perish? (Biology)

A new study shows how some species survive infectious disease epidemics, and how we can use this knowledge to assist and direct wildlife management.

Wildlife diseases are a major cause of wildlife decline around the world.

But despite their devastating effects, some wildlife species survive these disease epidemics and some populations even rebound, increasing their numbers.

Queensland’s Common Mistfrog populations have declined due to chytridiomycosis. Picture: Lee Skerratt/University of Melbourne.

Amphibians are some of the most threatened animals in the world, with over 30 per cent listed as vulnerable or endangered species on the International Union for Conservation of Nature (IUCN) list. And disease is a major cause of these declines.

But why do some species survive and others don’t?

To help answer this, Dr. Laura A Brannelly and her team decided to go through all of the relevant research literature to understand what makes a species thrive in natural conditions to improve species management outcomes, but also help avoid management mistakes.

They used amphibian declines as a case study for how best to understand the ways that species survive declines.

It turns out that for most species, they actually do not yet understand why they are persisting after disease caused declines.

This is partly because, as they show in their analysis, there is wide variation across species and life stages, which highlights the importance of community, where different species of frogs change disease impacts.

Even for species that have been heavily studied by different research teams, like the endangered common mist frog, Litoria rheocola, from the Australian tropics, they do not understand why some populations are surviving.

The fungal pathogen Batrachochytrium dendrobatidis causes the disease chytridiomycosis, which affects amphibian skin function. Picture: Shutterstock.

To help researchers better comprehend how species survive, they identified key criteria to guide future research that will help us understand the ways that populations rebound in the future.

They also show why we should use this information to improve management practices.

Frogs are declining globally due to the fungal pathogen Batrachochytrium dendrobatidis, known as Bd. The Bd fungus causes the disease chytridiomycosis, which affects amphibian skin function.

Amphibian skin is especially important for frogs because they use it to breath, absorb water and even maintain ions in their blood. This disease causes thickening of their skin, and disrupts the normal skin function in infected frogs, ultimately causing death due to cardiac arrest.

Chytridiomycosis occurs globally and has resulted in declines in over 500 species around the world in the last 50 years and has even caused 90 species extinctions including some species in Australia like the gastric brooding frog.

Many other species remain on the verge of extinction like the southern corroboree frog, which requires management to remain in the wild, including breeding programs, reintroductions and habitat management.

Despite these massive declines, there are some species who declined but then survived and remained, like the alpine tree frog, Litoria verreauxii alpina.

This species used to be widespread in the Australian Alps, but now remains at a handful of locations, although has remained stable at those locations for a couple of decades following the initial epidemic.

Even in some areas of pristine habitat, the alpine tree frog has gone extinct. Picture: Supplied.

In their latest study published in Ecology Letters, they highlight the conditions and traits that allow frogs to persist after an epidemic.

They found that frogs, like the alpine tree frog, can persist after their population has declined due to changes in the frog, such as through reproduction where infected animals actually increase their breeding behaviour or produce more offspring when infected.

Other frogs persist through increased resistance or tolerance to disease by evolving increased immunity or behaviour, such as avoiding disease or through regulating its body temperature by moving to warmer habitats or parts of habitats to help fight infection, a term called behavioural fever in ectotherms, commonly known as “cold-blooded” animals.

The habitat of the animals can also influence decline patterns because Bd thrives better in cooler, wetter habitats.

Frogs might also persist if virulence of the pathogen reduces over time which has not been observed but is possible.

And finally, an often overlooked way that animals can persist is through understanding how the disease is transmitted, and how the ecological community affects disease.

The alpine tree frogs are surviving because they are prioritising breeding and reproduction over increased immunity to the chytrid fungus. Picture: Laura Brannelly.

The ecological community includes the animals, plants and all other organisms in the frogs environment, and can include reservoir hosts that maintain disease in the system.

Reservoir hosts for the pathogen can be other species of frogs, but also include other organisms like crayfish that live with frogs. Reservoir hosts have a high tolerance to infection, meaning that they can carry high loads and not be impacted by the disease themselves.

In Australia a possible reservoir host is the southern brown frog, Litoria ewingii. And if a susceptible or threatened species, like the green and golden bell frog, Litoria aurea, live at sites with these reservoir hosts, then they might be more likely to decline.

Understanding the ways that species are persisting is important for management, because management actions will be more effective if we support how the animals are persisting naturally.

For example, the alpine tree frogs are surviving because they are prioritising breeding and reproduction over increased immunity. Since the arrival of chytridiomycosis, they are ensuring that they breed before succumbing to disease in a pond with permanent water, allowing the population to persist.

This means that management action should be focussed on supporting successful breeding and tadpole development and access to permanent water reserves.

If threatened species like the green and golden bell frog live at sites with fungus reservoir hosts, they might be more likely to decline. Picture: WikiCommons/Bernard Spragg

Through their research, they highlight that even with multiple decades of well-intentioned research devoted to understanding the impacts of chytridiomycosis on frogs, they know very little about how most species actually are persisting.

Without information to understand the ways that species persist after disease related declines, deciding on management actions is complicated. And even more importantly, it could lead to failure and exacerbate declines.

For example, for a species that is persisting at a low frog density which reduces transmission of Bd, adding captive-reared individuals to populations might increase the frog density and therefore increase transmission and disease within the population.

Without understanding how a species is persisting naturally, we could completely mismanage these threatened animals, and possibly lead to further declines.

They highlight that both researchers and managers need to work together, and research should be aimed at understanding the mechanisms of population persistence.

By using this knowledge we can plan management actions to support the ecology and biology of the species we are trying to save.

This work is a multi-institutional collaboration across the University of Melbourne, Griffith University, Southern Cross University, and international collaborations in the US and Spain.

Provided by University Of Melbourne

Bat-winged Dinosaurs That Could Glide (Paleontology)

Despite having bat-like wings, two small dinosaurs, Yi and Ambopteryx, struggled to fly, only managing to glide clumsily between the trees where they lived, according to a new study led by an international team of researchers, including McGill University Professor Hans Larsson. Unable to compete with other tree-dwelling dinosaurs and early birds, they went extinct after just a few million years. The findings, published in iScience, support that dinosaurs evolved flight in several different ways before modern birds evolved.

Life reconstruction of the bat-winged scansoriopterygid dinosaur Ambopteryx in a glide. Image credit: Gabriel Ugueto.

“We know some dinosaurs could fly before they evolved into birds,” says Professor Larsson, Director of McGill’s Redpath Museum. “What this shows us is that at least one lineage of dinosaurs experimented with a completely different mode of aerial locomotion. Gliding evolved countless times in arboreal amphibians, mammals, lizards, and even snakes – and now we have an example of dinosaurs.”

Yi and Ambopteryx were small animals from the Late Jurassic of China, living about 160 million years ago. Weighing in at about half a kilogram, they are unusual theropod dinosaurs. Theropods are carnivorous dinosaurs that include all birds alive today. Most theropods were ground-loving carnivores, but Yi and Ambopteryx were at home in the trees and lived on a diet of insects, seeds, and plants.

Map of the skeleton and preserved soft tissues of Yi. Image credit: Dececchi et al. 2020.

“Once birds got into the air, these two species were so poorly capable of being in the air that they just got squeezed out,” says lead author Thomas Dececchi, an assistant professor of biology at Mount Marty University. “Maybe you can survive a few million years underperforming, but you have predators from the top, competition from the bottom, and even some small mammals adding into that, squeezing them out until they disappeared.”

Little creatures could glide, not fly

Curious about how these animals could have flown, the researchers, scanned fossils using Laser-Stimulated Fluorescence (LSF), a technique that uses laser light to pick up soft tissue details of their wing membranes that can’t be seen with standard white light. Later, the team used mathematical models to predict how they might have flown, testing different variables like weight, wingspan, wing shape, and muscle placement.

“The results are clear these animals were not able to fly like birds,” says Larsson. “They didn’t have adaptations to even get close to the physical thresholds for powered flight, but their weird membranous wings do give them enough of an aerofoil to have glided. They are not comparable to living gliding squirrels or lizards but seem to have come up with a really novel way of getting a large enough wing membrane.”

Graphical summary of the major findings of the new study. Image credit: Dececchi et al. 2020.

Although gliding is not an efficient form of flight since it can only be done if the animal has already climbed to a high point, it probably did help Yi and Ambopteryx stay out of danger while they were still alive.

“Living gliders don’t travel long distances through the air,” says Dececchi. “It’s not efficient, but it can be used as an escape hatch. It’s not a great thing to do, but sometimes it’s a choice between losing a bit of energy and being eaten. Once they were put under pressure, they just lost their space. They couldn’t win on the ground. They couldn’t win in the air. They were done.”

The researchers are now looking more closely at the musculoskeletal anatomy of these bat-winged and other feathered dinosaurs that evolved around the origin of birds. “The diversity of dinosaurs just before the origin of birds amazes me,” Larsson says. “We used to think of birds evolving as a linear trend from their ground-dwelling dinosaur ancestry. We can know revise this textbook scenario to one that had an explosive diversity of experimentation, with dinosaurs evolving powered flight several times independently from birds, many having fully feathered wings but with bodies too heavy or wings too small to have gotten off the ground, and now, a weird bat-winged group of dinosaurs that were not only the first arboreal dinosaurs, but ones that glided! I feel like we are still just scratching the surface.”

References: “Aerodynamics show membranous-winged theropods were a poor gliding dead-end” by T. Alexander Dececchi, Arindam Roy, Michael Pittman, Thomas G. Kaye, Xing Xu, Michael B. Habib, Hans C.E. Larsson, Xiaoli Wang, and Xiaoting Zheng is published in iScience. DOI: http://dx.doi.org/10.1016/j.isci.2020.101574

Provided by McGill University

World’s Greatest Mass Extinction Triggered Switch To Warm-Bloodedness (Paleontology)

Mammals and birds today are warm-blooded, and this is often taken as the reason for their great success.

University of Bristol palaeontologist Professor Mike Benton, identifies in the journal Gondwana Research that the ancestors of both mammals and birds became warm-blooded at the same time, some 250 million years ago, in the time when life was recovering from the greatest mass extinction of all time.

The origin of endothermy in synapsids, including the ancestors of mammals. The diagram shows the evolution of main groups through the Triassic, and the scale from blue to red is a measure of the degree of warm-bloodedness reconstructed based on different indicators of bone structure and anatomy. Credit: Mike Benton, University of Bristol. Animal images are by Nobu Tamura, Wikimedia.

The Permian-Triassic mass extinction killed as much as 95 per cent of life, and the very few survivors faced a turbulent world, repeatedly hit by global warming and ocean acidification crises. Two main groups of tetrapods survived, the synapsids and archosaurs, including ancestors of mammals and birds respectively.

Palaeontologists had identified indications of warm-bloodedness, or technically endothermy, in these Triassic survivors, including evidence for a diaphragm and possible whiskers in the synapsids.

More recently, similar evidence for early origin of feathers in dinosaur and bird ancestors has come to light. In both synapsids and archosaurs of the Triassic, the bone structure shows characteristics of warm-bloodedness. The evidence that mammal ancestors had hair from the beginning of the Triassic has been suspected for a long time, but the suggestion that archosaurs had feathers from 250 million years ago is new.

Posture shift at the end of the Permian, 252 million years ago. Before the crisis, most reptiles had sprawling posture; afterwards they walked upright. This may have been the first sign of a new pace of life in the Triassic. Credit: animal drawings by Jim Robins, University of Bristol.

But a strong hint for this sudden origin of warm-bloodedness in both synapsids and archosaurs at exactly the time of the Permian-Triassic mass extinction was found in 2009. Tai Kubo, then a student studying the Masters in Palaeobiology degree at Bristol and Professor Benton identified that all medium-sized and large tetrapods switched from sprawling to erect posture right at the Permian-Triassic boundary.

Their study was based on fossilised footprints. They looked at a sample of hundreds of fossil trackways, and Kubo and Benton were surprised to see the posture shift happened instantly, not strung out over tens of millions of years, as had been suggested. It also happened in all groups, not just the mammal ancestors or bird ancestors.

Professor Benton said: “Modern amphibians and reptiles are sprawlers, holding their limbs partly sideways.

“Birds and mammals have erect postures, with the limbs immediately below their bodies. This allows them to run faster, and especially further. There are great advantages in erect posture and warm-bloodedness, but the cost is that endotherms have to eat much more than cold-blooded animals just to fuel their inner temperature control.”

The evidence from posture change and from early origin of hair and feathers, all happening at the same time, suggested this was the beginning of a kind of ‘arms race’. In ecology, arms races occur when predators and prey have to compete with each other, and where there may be an escalation of adaptations. The lion evolves to run faster, but the wildebeest also evolves to run faster or twist and turn to escape.

Something like this happened in the Triassic, from 250 to 200 million years ago. Today, warm-blooded animals can live all over the Earth, even in cold areas, and they remain active at night. They also show intensive parental care, feeding their babies and teaching them complex and smart behaviour. These adaptations gave birds and mammals the edge over amphibians and reptiles and in the present cool world allowed them to dominate in more parts of the world.

Professor Benton added: “The Triassic was a remarkable time in the history of life on Earth. You see birds and mammals everywhere on land today, whereas amphibians and reptiles are often quite hidden.

“This revolution in ecosystems was triggered by the independent origins of endothermy in birds and mammals, but until recently we didn’t realise that these two events might have been coordinated.

“That happened because only a tiny number of species survived the Permian-Triassic mass extinction – who survived depended on intense competition in a tough world. Because a few of the survivors were already endothermic in a primitive way, all the others had to become endothermic to survive in the new fast-paced world.”

References: Michael Benton, “The origin of endothermy in synapsids and archosaurs and arms races in the Triassic”, Gondwana Research, 2020. Doi: https://doi.org/10.1016/j.gr.2020.08.003 link: https://www.sciencedirect.com/science/article/pii/S1342937X20302252

Provided by University Of Bristol

Venom Glands Similar To Those Of Snakes Are Found For First Time In Amphibians (Paleontology)

Brazilian researchers discover that caecilians, limbless amphibians resembling worms or snakes that emerged some 150 million years before the latter, can probably inject venom into their prey while biting.

Upper jaw of a caecilian showing glands that expel a probably venomous secretion. © Carlos Jared, Butantan Institute

A group led by researchers at Butantan Institute in Brazil and supported by FAPESP has described for the first time the presence of venom glands in the mouth of an amphibian. The legless animal is a caecilian and lives underground. It has tooth-related glands that, when compressed during biting, release a secretion into its prey – earthworms, insect larvae, small amphibians and snakes, and even rodent pups. A paper reporting the study is published in iScience.

“We were analyzing the mucus glands in the skin of the animal’s head, which it uses to burrow down into the soil, when we discovered these structures. They’re located at the base of the teeth and develop out of the dental lamina, the tissue that typically gives rise to teeth, as is the case with snakes’ venom glands,” said Pedro Luiz Mailho-Fontana, first author of the paper and a postdoctoral intern at Butantan Institute with a scholarship from São Paulo Research Foundation – FAPESP.

An article by the same group published in 2018 in Scientific Reports showed that in addition to mucus glands in the skin all over the body caecilians have many poison glands in the skin of the tail as a passive defense against predators. This system, which is also found in frogs, toads and salamanders, poisons predators when they bite caecilians.

In the new report the researchers show that caecilians can be venomous, and indeed are the first amphibians to have an active defense system. Biologists apply the term venomous to organisms that bite or sting to inject their toxins, such as snakes, spiders, and scorpions, whereas poisonous refers to organisms that deliver toxins when touched or eaten.

In these caecilians, the secretion released by the glands also serves to lubricate a prey so that it is easier to swallow.

“Snakes have pouches to accumulate venom, which they inject through fangs when the pouches are squeezed by muscles. In rattlesnakes and pit vipers, for example, the teeth are hollow like hypodermic needles. In caecilians, gland compression during biting releases the venom, which penetrates the puncture wound. The same goes for lizards like the Komodo dragon and Gila monster,” said Carlos Jared, a researcher at Butantan Institute and principal investigator for the study.

The study was part of the FAPESP-funded project “Unraveling parental care in caecilians: nutritional and toxinological implications in Siphonops annulatus”. In a paper published in Nature in 2006, the researchers were the first to show that offspring of the caecilian species Boulengerula taitanus feed solely on the mother’s skin in the first two months of their lives. In 2008 the group described the same behavior for Siphonops annulatus in a paper published in Biology Letters .

Except for a group that lives in aquatic environments, caecilians spend their entire lives in burrows or underground tunnels. As a result, they have very small eyes, which sense light but do not form images. They are also the only vertebrates that have tentacles. In caecilians, these are near the eyes and act as feelers equipped with chemical sensors that test the environment for sensory data.

Characterization of venom

The researchers’ biochemical analysis showed that the secretion released from the animal’s mouth while it is biting contains phospholipase A2, an enzyme commonly found in the venom of bees, wasps, and snakes. They found the enzyme to be more active in caecilians than in rattlesnakes. However, this trait is not sufficient to prove they are more venomous than snakes.

The group will now conduct tests using molecular biology techniques to characterize caecilians’ dental gland secretion more precisely and confirm that it is venomous. In the future they may test any proteins they find in order to explore possible biotechnological applications such as drug development.

Four species were analyzed in the study. In Typhlonectes compressicauda, the only one that lives in aquatic environments, the glands were found only in the lower jaw. The researchers believe it may have lost the upper-jaw glands during the evolutionary process (as did some water snakes) since the water in the environment naturally lubricates prey. The mandibular glands were retained, probably for venom.

Most of the 214 known species of caecilians live underground in the humid forests of South America, India, and Africa. Owing to their subterranean habits, biologists rarely have a chance to find out more about these animals.

More than new data about caecilians, the study offers important information regarding the evolution of amphibians and reptiles. “For snakes and caecilians, the head is the only tool for exploring the environment, fighting, eating and killing. This may have fueled evolutionary pressure for these limbless animals to develop venom,” said Marta Maria Antoniazzi , also a researcher at Butantan Institute and a co-author of the study.

References: Pedro Luiz Mailho-Fontana, Marta Maria Antoniazzi, Cesar Alexandre, Juliana Mozer Sciani, Edmund D. Brodie Jr.
Carlos Jared, “Morphological Evidence for an Oral Venom System in Caecilian Amphibians”, Vol. 23, issue 7, 101234, 2020. DOI: https://doi.org/10.1016/j.isci.2020.101234 link: https://www.cell.com/iscience/fulltext/S2589-0042(20)30419-3?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS2589004220304193%3Fshowall%3Dtrue