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Amphibians

Submitting your sightings is now quicker and easier

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Froglife’s new and improved Dragon Finder app is here.  The app helps you to identify amphibians and reptiles, find out more about individual species and submit a record of your sighting.  Collecting records is a vital first step in wildlife conservation.  This data provides the evidence needed to protect important sites and alert us to population declines.  

Dragon Finder app users will find all the great features of the original version but now with a simpler process for submitting your records, many technical improvements and compatibility with recent models of mobile phones.  Existing users will simply be asked to update the app the next time they open it.

Froglife submit all the records collected through the Dragon Finder app to the National Biodiversity Network (NBN) to be shared publicly on the NBN Atlas.  Many of the improvements that we’ve made to the app and supporting database mean that the records are now in better shape to be submitted to this platform and local biodiversity record centres.  In short this means that the records you submit are now even more valuable.

The Dragon Finder App was first launched in 2014 and is funded by the National Lottery Heritage Fund.

Amphibians and reptiles are the most threatened species globally and also the least recorded.  For successful conservation of these fascinating creatures we need to understand their national distribution and population trends. 

Froglife’s CEO, Kathy Wormald says “We are delighted to be launching this much needed new version of the app.  To support Froglife’s work conserving UK amphibians and reptiles we ask everyone to download the app and submit their sightings”.

Find out more

Croaking Science: Captive Breeding, Conservation and Welfare of Amphibians.

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In general, Froglife does not encourage the keeping of amphibians (or reptiles) in captivity. Unlike the animals which have become used to close contact with people through the long process of domestication (farm animals and those that we treat as pets, or ‘companion animals’), there are no domesticated species of amphibians. We accept that people, especially children, can become fascinated and enthused by keeping newts, frogs or tadpoles, and that this can develop into a life-long interest that may encourage that person to contribute to the cause of wildlife conservation. However, the needs of amphibians are complex, and too often ignorance of these needs can lead to suffering and needless death in captivity. This can be particularly the case for non-native species when we add the traumas of being captured in the wild, international transportation, and being put on display for sale in a pet shop. Captive breeding of non-native species can alleviate some of this stress, but not the lottery of being cared for by enthusiastic but inexperienced keepers. Overall then, it is preferable for people to learn about amphibians from books, the media, wildlife ponds in private gardens and allotments, visits to wildlife sites where they can be encountered in their native habitats….and zoos.

Froglife recognises well-managed zoos (and aquaria) as exceptions to our policy against keeping amphibians in captivity. As well as having a broadly educational role concerning the world’s wildlife, zoos aspire to be an important component of the worldwide effort to conserve biodiversity. Where a species is threatened with extinction in the wild, it may be possible to take a small population into captivity and encourage them to breed, establishing a reserve population which can be used to re-populate the natural habitat when favourable conditions return. This practice is known as ex situ conservation. In this article, I review progress on ex situ conservation of amphibians and ask how well zoos are meeting their welfare needs.

The first Global Amphibian Assessment (Stuart et al., 2004) concluded that amphibians are the most threatened of the vertebrate classes, with about one third of species facing extinction. One response to this finding was the launch in 2007 of the Amphibian Ark (AArk) by a consortium of the IUCN and the World Association of Zoos and Aquaria. Its strategy is to identify threatened species whose survival chances could be improved by an interventionist programme including in-country and out-of-country captive breeding, allied to efforts to mitigate local threats to the species in the wild (Pavajeau et al., 2008). The AArk Newsletter, published quarterly, on open access, provides information on the progress of AArk programmes worldwide.

A major concern is highlighted by a team from Cologne Zoo (Jacken et al., 2020). They surveyed amphibian holdings in 4519 zoos and aquaria. Only about 7% of known amphibian species (=540 species) are currently kept in zoos. The three classes of amphibians are very unevenly represented, with 17.4% of newts and salamanders (=121 species), 6.1% of frogs and toads (=411 species) and only 3.9% of caecilians (= 8 species). Worse still, more than 10% of holdings are just single specimens; breeding success, even when larger populations are kept, is not high; and three quarters of the species kept are not threatened in the wild. Jacken et al. note that their survey did not include a number of good ex situ conservation programmes being run in university departments and museums, but they concluded overall that zoos are not fulfilling the aims of AArk. There can be several explanations for this situation. Although amphibians might seem highly suitable animals for ex situ conservation (for example, they are small, so do not require a lot of space; and they often have high reproductive outputs, with individuals maturing in a short time), in other ways they are highly problematic. For example, they are mostly nocturnal, so active when visitors are absent. Zoos depend for their incomes on paying customers, and need to prioritise species that people like to see. In addition, adult amphibians need live food, mostly insects, and this requires an efficient production facility. The high reproductive output of amphibians can also be a problem: once tadpoles have metamorphosed, how to keep the hundreds, perhaps thousands of offspring when space may be limited? And then there is disease: the high risks to the entire breeding facility from a chytrid outbreak requires a strict biosecure regime, incompatible with visitors (Pessier, 2008).

If AArk is to become successful, it clearly has to do better in encouraging zoos and other wildlife collections to hold more breeding populations of amphibians, prioritising threatened species (as long as a careful assessment concludes that ex situ conservation is an appropriate solution to the threats these species face). However, there is another issue: the psychological welfare of amphibians. There are several manuals of advice on amphibian husbandry, the most authoritative being Poole and Grow’s (2012) resource guide. This deals with food, water, housing, lighting, disease prevention etc. but, like most such guides does not cover behavioural and cognitive aspects of welfare. It has long been recognised that, in captivity, mammals and birds can suffer psychological distress from the lack of stimulation in their environment. This often manifests in the development of repetitive, sometimes self-damaging behaviours known as stereotypies. To avoid these, good zoo-keepers have devised a wide range of husbandry interventions, collectively known as ‘enrichments’, which provide the animals with interests and activities that promote psychological well-being (Young, 2003).

As well as promoting good mental health, enrichments can have another general purpose. Where animals are kept with ex situ conservation in mind, there is a need to prepare them for release into the wild. Enrichments can provide experience of ‘outside’ behaviours such as foraging, predator avoidance and mate-finding, without which survival in the wild is likely to be very brief.

In amphibians (and reptiles), there has been a tendency to believe that their behaviours are so simple and pre-programmed that enrichments are unnecessary. In a rebuttal of Dodd and Seigel’s (1991) critique of ex situ conservation for amphibians, Bloxam and Tonge (1995) wrote that amphibian ‘behaviours are less dependent on learning and environmental experience than those of birds and mammals…It has always seemed apparent to herpetologists that, with their relatively r-selected life history strategies1 and their low levels of behavioural complexity, amphibians should be ideally suited to short or medium-term conservation strategies’. These claims were accompanied by not a single supporting reference. It is worth contrasting these attitudes with work on fish, like amphibians, cold-blooded vertebrates and with a similar level of brain development. Much research, related to improving the welfare of fish in aquaculture, has shown that learning is important and that fish can suffer from pain and distress (Sneddon, 2015; Sloman, 2019). In addition, enrichments can promote the development of life-skills in fish (Salvanes, 2013). If this is the case for fish, why not for amphibians?

The most detailed discussion of enrichment in amphibians is the review by Michaels et al. (2014), subtitled ‘a neglected topic’. In comparison with the hundreds of papers on enrichment in mammals, Michaels et al. found only 14 relevant primary research papers on amphibians, and I have noted only a small number published since 2014. An issue is that ‘enrichment’ is rarely used in the titles, abstracts or key-words of papers related to husbandry in amphibians, whereas it is commonly used in the mammal literature. This in itself indicates that the amphibian research community has not yet taken the concept of enrichment on board. One sign of progress, however, comes from a comparison of the amphibian chapters in the 1999 and 2010 editions of the Universities Federation for Animal Welfare handbook, which recommends good practice for animals kept for use in laboratories. The main laboratory amphibian, since its earlier use in testing for human pregnancies, is still Xenopus laevis. The chapter by Halliday (1999) makes no mention of enrichment, but Tinsley (2010) discusses several aspects of enrichment such as the provision of covers and shelters. In addition to studies on shelters and their behavioural and physiological benefits, Michaels et al. found papers on the benefits of behavioural complexity: ramps, perches and ‘caves’ improved the welfare of bullfrogs. However, papers on the provision of complex habitats for amphibians too rarely investigate which features make a measurable difference in behaviour (for example, McRobert, 2003). In mammals, enrichments which encourage exploration of the enclosure and active foraging for food have been found to have considerable welfare benefits. We tend to think of amphibians as ‘sit-and-wait’ predators, but some species are active foragers. Michaels et al. found a few papers that investigated the welfare effects of varied food delivery techniques. Altering the position of a food dish increased activity levels in dendrobatid frogs, considered as a benefit. This, of course, raises the question: by what criteria do we consider the welfare of a captive amphibian to be improved? The small number of research studies to date means that this key question remains to be fully explored.

This article is intended as an introduction to the topic of welfare and enrichment, with a focus on amphibians. In a future article to appear in Froglife’s magazine Natterchat, I will review studies on reptiles.

Note 1: r-selected species generally have many offspring, limited parental care and short lives, as compared to K-selected species with small numbers of offspring, often prolonged parental care and long lives. Actually, some amphibians have complex parental care provision, small offspring numbers and some have long lives. In any case, it is not clear why Bloxam and Tonge feel there is a link between r-selected life histories and suitability for ex situ conservation.

Written by: Roger Downie Trustee, Froglife; Honorary senior lecturer, University of Glasgow

References

Bloxam and Tonge (1995). Amphibians are suitable candidates for breeding-release programmes. Biodiversity and Conservation 4, 636-644.

Dodd and Seigel (1991). Relocation, repatriation and translocation of amphibians and reptiles: are these conservation strategies that work? Herpetologica 47, 336-350.

Halliday (1991). Amphibians. In: Poole, T., editor. UFAW Handbook, 7th edition volume 2. Ps 90-102.

Jacken et al. (2020). Amphibians in zoos: a global approach on distribution patterns of threatened amphibians in zoological collections. International Zoo Yearbook 54, 146-164.

McRobert (2003). Methodologies for the care, maintenance and breeding of tropical poison frogs. Journal of applied animal welfare science 6, 95-102.

Michaels, Downie and Campbell-Palmer (2014). The importance of enrichment for advancing amphibian welfare and conservation goals: a review of a neglected topic. Amphibian and Reptile Conservation 8, 7-23.

Pavajeau et al. (2008). Amphibian Ark and the Year of the Frog campaign. International Zoo Yearbook 42, 24-29.

Pessier (2008). Management of disease as a threat to amphibian conservation. International Zoo Yearbook 42, 30-39.

Poole and Grow, editors (2012). Amphibian Husbandry Resource Guide. Association of Zoos and Aquariums.

Salvanes et al. (2013). Environmental enrichment promotes neural plasticity and cognitive ability in fish. Proceedings of the Royal Society B 280, 1767.

Sloman et al. (2019). Ethical considerations in fish research. Journal of Fish Biology 94, 556-577.

Sneddon (2015). Pain in aquatic animals. Journal of experimental biology 218, 967-976.

Stuart et al. (2004). Status and trends of amphibian declines and extinctions worldwide. Science 306, 1783-1786.

Tinsley (2010). Amphibians, with special reference to Xenopus. In: Hubrecht and Kirkwood, editors. UFAW Handbook 8th edition. Ps 741-760.

Young (2003). Environmental enrichment for captive animals. Blackwell, Oxford.

Acknowledgements

Thanks for feedback on the first draft of this article from Kathy Wormald and Sheila Grundy.

 

 

 

 

The Road to Success? Experts share research at our Wildlife Road Mortality Conference.

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The Road to Success? Experts map route to try and safeguard wildlife in the future (written by Jules Robinson). 

The UK’s planned transformative infrastructure developments must not be at the expense of the countries wildlife, concluded experts at Froglife’s Widlife Road Mortality Webinar. Wildlife conservationists from around the world came together online at 1pm on 10th March 2021 to discuss their work in relation to mitigating the death of wildlife on our roads.

Froglife’s CEO, Kathy Wormald, introduced the webinar by sharing the work of Froglife over the past 30 years, particularly with regards to Froglife’s ‘Toads on Roads Campaign’ where thousands of volunteers take part each year to help toads and frogs successfully navigate roads on the way back to their spawning ponds to breed. Froglife is also currently running a Wildlife Tunnel Campaign, having undertaken research at a number of highway crossings for smaller wildlife including toads, demonstrating that for relatively small costs, tunnels and grids can be included in road schemes which provide a safe crossing for many other species.  Common Toad populations have declined by an estimated 68% in the last 30 years, and roads are a key factor. Research has also recently shown that in addition to the death of the adults, going to spawn, a few months later there are thousands of small toadlets, migrating from their spawning ponds into the countryside which are killed and not seen. The creation of balancing ponds and drainage ditches next to roads only exacerbates the situation.

Did you know that 1/5 of the Earth’s terrestrial surface is located within 1km of roads and that up to 100million animals die on roads around the world each year?  Badgers and pheasants top the list for the most common mammal and bird species in the UK, according to figures provided by Dr Sarah Perkins, co-ordinator of Project Splatter, a citizen-science monitoring scheme for wildlife vehicle collisions across the UK. Their research has also shown that 95% of the public are interacting with wildlife more by seeing it dead on the roads, than seeing it alive in the wild.

Citizen science proved to be a strong theme throughout. Debobroto Sircar (aka Debo), Head of Species Recovery and Wildlife Crime Control Division, Wildlife Trust of India spoke of the successful launch of RoadWatch, a user-friendly smartphone app that they’ve encouraged members of the public to use, which gathers necessary data such as photographic records, GPS location, type of animal, date of record etc. The app can transmit the data in less than a minute, with minimal effort and has helped them successfully map roadkill hotspots, identifying India’s most affected species so they can instigate mitigation measures, including signs, fencing and road closures at different times of the year. Their ‘#I brake for wildlife’ social media and car sticker campaign has also created awareness and is gradually reducing the incidence of wildlife road kills across the country and signs put up at rail crossings notifying train drivers of elephant corridor areas has also had a huge effect in reducing speed and the number of elephants being hit.

Dr Sean Boyle, a postdoctoral researcher at the Memorial University of Newfoundland, also recognised the importance of engagement and outreach activities, particularly involving youth, and he too mentioned a range of mitigation measures including the closure of roads such as one in Ontario for salamanders to make their yearly migration. He also spoke of recognising road mortality, as not just the roadkill itself seen on the surface of a road, but the ‘Road Effect Zone’ which is the area surrounding the road that an animal won’t approach or go near because of a combination of factors including pollution, light or sound and the fragmentation of habitat. His research has indicated this can be between 2-5km for some species. He also reminded us that we should include the effects of railways on wildlife mortality and the area around the tracks. Following on from his surveys into reducing the harmful impacts of roads and evaluation on the success of fences and crossing structures, he summarised that to best avoid wildlife road mortality humans need to modify their behaviour. Whilst he recommended the use of signage and putting up fencing directing wildlife to tunnels, he also recognised that people who regularly use the same route, initially reacted to the road awareness signs but then became less receptive as they got used to them.  Tunnels are costly and mitigation should be thought of at the time of construction.

Fragmentation was a key concern of both Froglife’s Reptile Project Officer, Ben Harris and author and ecologist Hugh Warwick. Ben spoke of the lack of desperately needed reptile road mortality research in the UK but that European data has indicated that despite the noise and ground vibrations from traffic, reptiles are still susceptible to road collisions, especially on smaller roads when adjacent to their preferred habitat and they may be attracted to the warm tarmac to bask. In the UK adders exist in small numbers so even if 1 or 2 are killed this could lead to a genetic imbalance. He suggested that we may need to adapt and install tunnels that reptiles will use it like the ‘Herpetoduct’ in the Netherlands, to reduce reptile road mortality and help stop fragmentation.

Hugh Warwick, a spokesperson for the British Hedgehog Protection Society, continued with this theme – as he told us that habitat fragmentation is one of the most serious threats to face hedgehogs. Whilst 167-335,000 hedgehogs were killed on the roads in a study undertaken in 2004, the current road kill estimate is 100,000 a year because of the hedgehog populations overall decline. He told us that with a starting population of 32 hedgehogs they would need 90km of unrestricted landscape not fragmented by fences, roads, lakes or ditches (created alongside roads to stop flooding, which can act as pitfalls). He called for all new infrastructure to have eco-ducts built in such as in the Netherlands, the A556 near Knutsford in the UK or the tunnels built over the A3 near Hindhead. “We need to start making our case for the value of nature and how life-giving it is”, he summarised at the end of his presentation which was the final talk.

Professor Roger Downie, Froglife Trustee who hosted the event agreed, “A big message coming loud and clear from to-day’s timely Froglife webinar on ‘Wildlife Mortality on Roads’ was that the UK’s planned transformative infrastructure developments must not be at the expense of the country’s wildlife. Wildlife needs safe routes to travel through our landscapes, and these must be built into all developments.”

Kathy Wormald, Froglife CEO concluded by saying, “We are extremely pleased with how the webinar went today, it has certainly raised the bar for action to be taken to stop the carnage of wildlife death on the worlds roads. Let’s collectively take positive action to bring this matter to a halt.  We know that it is impacting on the sustainability of wildlife across the globe resulting in population declines and in some instances extinction.  Governments need to take this matter seriously and help conservationists to address this issue.”

You can watch a recording of the webinar here: www.froglife.org/webinars

To sign Froglife’s Wildlife Tunnel Campaign please click here. 

Croaking Science: Venomous Amphibians

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Venomous animals are able to inject their toxins into another organism while poisons are ingested, inhaled and absorbed. The ability to deliver venom into another animal has distinct evolutionary advantages such as in defence, prey capture and even sexual selection.

Amphibians secrete a wide variety of compounds from their skin glands. Generally, mucous glands help provide a moist coating on their skin to facilitate cutaneous respiration while granular glands secrete substances that amphibians use as a chemical defence against predators (eg. toxic and noxious compounds) and microorganisms (eg. antimicrobial peptides). This is sometimes displayed with bright, aposematic colouration (Duellman and Trueb 1996). 

Many different toxic secretions have been found in amphibian skin which act in numerous ways to disrupt the physiology of potential enemies (Daly et al. 2005, Savitzky et al. 2012).  For example, newts in the genera Taricha and Notophthalmus synthesise tetrodotoxins in high concentrations and are co-evolving in an evolutionary arms race with Thamnophis garter snakes where toxicity is a selective pressure (Brodie et al. 2005, Mailho-Fontana et al. 2019, Hague et al. 2020).  Fire salamanders secrete samandarin alkaloids through their paratoid glands which can cause convulsions, hypertension and respiratory paralysis in potential predators.  Frogs can sequester an array of toxins such as the potent neurotoxin Zetekitoxin in the Panamanian golden frog and the batrachotoxins in highly toxic Phyllobates poison frogs (Duellman and Trueb 1996).  The bright yellow Australian corroboree frogs of the genus Pseudophryne synthesise their own pseudophrynamine toxins as well as sequestering pumiliotoxins from their environment to deter predators (Smith et al. 2002). Fossorial caecilians are also known to produce defensive toxins with poison glands being discovered on the tails of Siphonops annulatus ringed caecilians as a possible defence against predators as they burrow into the soil (Jared et al. 2019). 

Venom, however, is rare in amphibians with only a few species possessing a system to deliver their toxins into another organism. 

The Iberian ribbed newt (Pleurodeles waltii) is a fascinating salamandrid from Spain and Portugal with an incredible defence behaviour. They have the ability to use their ribs to protrude through the skin to envenomate and ‘sting’ a predator. When distressed these newts can flatten themselves or arch their backs in an antipredator posture. They will then rotate their ribs 65° forwards which increases the angle of the spine to allow its ribs to penetrate through the skin wall and project as ‘spines’. This allows them to coat their ribs with a viscous, milky substance from their skin tubercles and inject it into the mouth of the predator making them unpalatable and allowing them to escape (Heiss et al. 2010). This defence mechanism doesn’t cause any permanent damage as antimicrobial peptides are able to prevent infection in the lacerated skin and their tissue is able to regenerate remarkably quickly. The tip of the ribs are also covered with a periosteum layer which is also thought to prevent microbial infection when the ribs puncture the skin.

The Echinotriton genus of crocodile newts are a sister group to the sharp ribbed newt and are also able to use their ribs to pierce their body wall when attacked by predators (Brodie et al. 1984).  

Sharp ribbed newt (Pleurodeles walti)

Brazil is home to two tree frogs which have incredible cranial morphologies and venomous defensive mechanisms. The Greening’s frog Corythomantis greeningi live in the semi-arid caatinga ecosystem of Eastern Brazil and conceal themselves in tree hollows and rock crevices to stay moist and evade predators. Bruno’s casque headed frog Aparasphenodon brunoi is another endemic Brazilian hylid with a fascinating skull morphology. They inhabit lowland tropical forests and shrubland and like C. greeningi, will hide in water-filled tree or bamboo hollows and bromeliad phytotelmata. 

Both of these peculiar frogs have flattened, casqued heads with their skin co-ossified with underlying bones. They use their heads to aid in a behaviour known as phragmosis (Jared et al. 2006, Blotto et al. 2020).  Phragmosis occurs when an animal enters a hole and blocks the entrance with their head to defend themselves from predators. In the lab, these frogs will exhibit this behaviour by entering test tubes backwards and blocking themselves off with their casqued heads. This phragmotic behaviour along with their venomous spines means these frogs have never been observed being predated in the wild. It is also thought that cranial ossification and phragmosis also indirectly reduces water loss and prevents desiccation by creating a humid microclimate within their tree holes (Jared et al. 2006). 

These frogs have bony spines, ridges and protrusions on their skulls in areas with high concentrations of granular and mucous glands which secrete a potent venom. Their mobile heads allow the frogs to deliver the venom into animals via head-butting and jabbing with their spines which are coated with the toxic secretions as the spines pierce their venom glands. This provides a highly effective chemical defensive mechanism as the toxin coupled with the wound caused by the head spines ensures would-be predators have a bad time when they attempt to ingest these frogs (Jared et al. 2015). Their cutaneous secretions include alkaloids and steroids which can induce oedema and intense pain in predators (Mendes et al. 2016). The venom contains both proteolytic and fibrinolytic agents as well as hyaluronidase which aids the toxins in diffusing around their enemies’ bodies (Jared et al. 2015). 

The venom of Greening’s frog is thought to be twice as lethal as fer-de-lance snakes of the genus Bothrops while Bruno’s casque headed frog secretes a venom 25x as toxic as these notorious neotropical vipers with an LD50 of 94.8µg in mice. A single gram of A. brunoi venom could kill 300,000 mice or 80 humans (Jared et al. 2015)!  However, A. brunoi has smaller spines and granular glands than C. greening and so may not be able to inject as much venom when defending against a predator. 
Top: Bruno’s casque headed frog (Aparasphenodon brunoi) L: Renato Augusto Martins R: Carlos Jared 
Bottom: Greening’s frogs (Corythomantis greeningi) Carlos Jared 

 

There are many other frogs with complex cranial morphology including immense variation in skull shape and hyperossification which often relate to their interesting and diverse ecologies (Paluh et al. 2020). With an array of other anurans having mineralised and spiny skulls, it is possible that there are a few more venomous frogs which are waiting to be studied. Contenders include the fascinating shovelhead tree frog Triprion, the crowned tree frog Anotheca spinosa and Polypedates ranwellai (Jared et al. 2015). 

In a recent paper by Mailho-Fontana et al. 2020, a new set of specialised dental glands were discovered in Brazilian ringed caecilians (Siphonops annulatus) that may produce venomous enzymes – but further research is needed to confirm this. These enzymes were demonstrated to have gelatinolytic, caseinolytic and fibrinogenolytic properties. This incredible discovery may allow researchers to rethink the evolution of venom in vertebrates (since it could have evolved independently in both amphibians and reptiles) and inspire new studies about caecilian toxinology.

Through histological and biochemical analysis of saliva samples, researchers found A2 phospholipase enzymes which could mean that some fossorial caecilians inject venomous saliva via these dental glands into their earthworm prey in order to incapacitate and digest them. These enzymes are found in many other venomous creatures such as scorpions, snakes and insects. It is also worth noting that many venoms have originated as saliva such as in komodo dragons, shrews, bats and slow lorises making the prospect of venomous gymnophiones very exciting!

Other caecilians including the basal genus Rhinatrema showed similar dental glands to the ringed caecilians which could suggest that caecilians evolved to inject oral venom early on in their evolution (Jared et al. 2020). 

Written by Xavier Mahele

References

Blotto, B.L., Lyra, M.L., Cardoso, M.C., Trefaut Rodrigues, M., R. Dias, I., Marciano‐Jr, E., Dal Vechio, F., Orrico, V.G., Brandão, R.A., Lopes de Assis, C., Lantyer‐Silva, A.S., Rutherford, M.G., Gagliardi‐Urrutia, G., Solé, M., Baldo, D., Nunes, I., Cajade, R., Torres, A., Grant, T., Jungfer, K.‐H., da Silva, H.R., Haddad, C.F. and Faivovich, J. (2020) The phylogeny of the Casque‐headed Treefrogs (Hylidae: Hylinae: Lophyohylini). Cladistics

Brodie, E.D., Feldman, C.R., Hanifin, C.T. et al. (2005) Parallel Arms Races between Garter Snakes and Newts Involving Tetrodotoxin as the Phenotypic Interface of Coevolution. Journal of Chemical Ecology 31, 343–356.

Brodie, E., Nussbaum, R., & Marianne DiGiovanni. (1984) Antipredator Adaptations of Asian Salamanders (Salamandridae). Herpetologica, 40(1), 56-68.

Daly, J. W., Spande, T. F. & Garraffo, H. M. (2005) Alkaloids from Amphibian Skin:  A Tabulation of Over Eight-Hundred Compounds. Journal of Natural Products 68, 1556–1575 

Duellman, W. E. & Trueb, L. (1996) Biology of Amphibians. McGraw-Hill.

Hague, M.T.J., Stokes, A.N., Feldman, C.R., Brodie, E.D., Jr. and Brodie, E.D., III. (2020) The geographic mosaic of arms race coevolution is closely matched to prey population structure. Evolution Letters 4: 317-332.

Heiss, E., Natchev, N., Salaberger, D., Gumpenberger, M., Rabanser, A. and Weisgram, J. (2010), Hurt yourself to hurt your enemy: new insights on the function of the bizarre antipredator mechanism in the salamandrid Pleurodeles waltl. Journal of Zoology 280: 156-162.

Jared, C., Antoniazzi, M.M., Navas, C.A., Katchburian, E., Freymüller, E., Tambourgi, D.V. and Rodrigues, M.T. (2005) Head co‐ossification, phragmosis and defence in the casque‐headed tree frog Corythomantis greeningi. Journal of Zoology 265: 1-8.

Jared C, Mailho-Fontana PL, Antoniazzi MM, Mendes VA, Barbaro KC, Rodrigues MT, Brodie ED (2015) Venomous Frogs Use Heads as Weapons. Current Biology Volume 25, Issue 16,

Jared, C., Mailho-Fontana, P.L., Marques-Porto, R. et al. (2018) Skin gland concentrations adapted to different evolutionary pressures in the head and posterior regions of the caecilian Siphonops annulatus. Scientific Reports 8, 3576.

Mailho-Fontana, P.L., Jared, C., Antoniazzi, M.M. et al. (2019) Variations in tetrodotoxin levels in populations of Taricha granulosa are expressed in the morphology of their cutaneous glands. Scientific Reports 9, 18490.

Mailho-Fontana, P. L. et al. (2020) Morphological Evidence for an Oral Venom System in Caecilian Amphibians. iScience 23, 101234.

Mendes VA, Barbaro KC, Sciani JM, Vassão RC, Pimenta DC, Jared C, Antoniazzi MM. (2016) The cutaneous secretion of the casque-headed tree frog Corythomantis greeningi: Biochemical characterization and some biological effects. Toxicon Volume 122.

Paluh D, Stanley EL, Blackburn DC. (2020) Evolution of hyperossification expands skull diversity in frogs. Proceedings of the National Academy of Sciences 117 (15) 8554-8562.

Savitzky, A.H., Mori, A., Hutchinson, D.A. et al. (2012) Sequestered defensive toxins in tetrapod vertebrates: principles, patterns, and prospects for future studies. Chemoecology 22, 141–158.

Smith, B. P. et al. (2002) Evidence for Biosynthesis of Pseudophrynamine Alkaloids by an Australian Myobatrachid Frog (Pseudophryne) and for Sequestration of Dietary Pumiliotoxins. Journal of Natural Products 65, 439–447.l

 

Croaking Science: How many amphibian species are there, how do we know, and how many are threatened with extinction?

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I’m sure most Froglife supporters and Croaking Science readers will be aware that the world’s amphibian species are in crisis. However, you may not know just how bad the crisis is, and how we know about it. This Croaking Science article aims to show how strong the evidence is, how it is gathered, and how difficult it is to keep up to date.

Herpetologists began to become aware in the 1990s that, although all kinds of wildlife were in trouble all over the world, amphibians were a special case. Simon Stuart and colleagues put numbers to this feeling in 2004. Their Global Amphibian Assessment estimated that 32.5% of amphibian species were globally threatened (i.e. they fitted into the IUCN Red List categories Critically Endangered, Endangered or Vulnerable: see later for definitions) compared to 12% of birds and 23% of mammals. Further, 22.5% of amphibians fell into the Data Deficient category i.e. too little was known about their status to make an assessment, a substantially higher proportion than for birds and mammals whose status tends to be better known. This meant that only about 44% of amphibian species could be classed as of Least Concern.  Stuart and colleagues discussed possible reasons for amphibians being in worse shape than the other mainly terrestrial vertebrate groups (at that time, too little was known about the status of reptiles to make a similar estimate for them). Although anthropogenic habitat loss and change were the underlying main causes for all wildlife declines, amphibian populations seemed to be declining even in good quality habitat, for what Stuart et al. called ‘enigmatic’ reasons. Within a few years, it was clear that the main cause of the ‘enigma’ was the spread of the fungal disease chytridiomycosis against which many amphibian species had no or only very limited resistance. It is interesting in a time of a global pandemic affecting the human population to reflect on the causes and effects of a novel disease affecting wildlife.

Stuart et al.’s assessment was based on the then total number of described amphibian species, 5743. However, James Hanken (1999) had earlier noted the irony that, at a time when amphibian species were in severe decline, the number of known species was rapidly increasing. This trend has continued. The Amphibian Species of the World website (Frost, 2020) currently (October, 2020) lists 8226 species, a 43% increase on the number assessed by Stuart et al. in 2004. Over the last 10 years, the number of described species of amphibians (mostly anurans: frogs and toads) has increased on average by 150 per year.

How has this happened? The biggest discoveries of new species are in the tropics where amphibian diversity is highest, and where, until recently, resources and expertise for amphibian research were very limited. Amphibians are mostly small, mainly active at night, and often quite localised, all of which create difficulties in cataloguing biodiversity.  It also turns out that external appearances can conceal underlying differences, so that it is only recently, with the availability of DNA sequencing, that herpetologists can work out that some species, previously thought to have extensive ranges, should really be split into several distinct species. Over my time studying the frogs of Trinidad and Tobago, new species descriptions of this kind have occurred in several cases. For example, the stream frogs of northern Venezuela, Trinidad and Tobago (see Croaking Science September 2020 for an account of colour changes in these frogs) were earlier thought to belong to one species: now they are three, Mannophryne trinitatis, M. olmonae and M. venezuelensis. Will this process of finding new amphibian species come to an end? Presumably it will, but currently there is no sign of the new discovery trend slowing down.

How do we establish the conservation status of a species? The task of keeping tabs on amphibians falls to the IUCN Species Survival Commission’s Amphibian Specialist Group (ASG). Their aim is to ‘provide the scientific foundation to inform effective amphibian conservation around the world’. A key part of their work is the compilation and revision of the Amphibian Red List i.e. an assessment of all species relative to their status in the wild. The main Red List categories (IUCN, 2001), with their definitions, and the current proportions of amphibian species in each category (from a total of 6932 species) are shown below:

Category, definition, percentage of amphibian species  

Critically endangered (CR): extremely high risk of extinction in the wild, 8.9%

Endangered (EN): very high risk…, 14.4%

Vulnerable (VU): high risk…., 9.8%

Near threatened (NT): close to qualifying as threatened, 5.6%

Least concern (LC): widespread and abundant, 41.5%

Data deficient (DD): inadequate information available to make an assessment, 19.3%

There is a final category of ‘not evaluated’: these are mainly newly identified species for which information on their population status is often very limited. Where new species have been named from the splitting of a widespread species, this causes a particular problem for the Red Listing process. For example, the widespread small tree frog Dendropsophus minutus is an abundant neotropical LC species; the population in Trinidad is now classed as a Trinidad endemic, D. goughi, so its status now needs assessed separately.

Clearly, a species’ status can change with time, so the Red List needs regular updating. In addition, as noted above, the identification of new species means there is a constant need for new assessments. At present, the ASG is nearing completion of a major re-assessment, due for release in December 2020: it will be fascinating to find how amphibians as a whole have fared since the last major revision in 2010.

What sort of evidence goes into determining a species conservation status? The Red Listing process is as objective as possible and relies on input from experts around the world. Key questions are: have populations changed, and if so, by how much? What is the geographic range of the species, and how much of this range does it occupy? How large or small is the population?  These can be quite difficult questions to answer with any degree of certainty. Consider the UK, with its considerable resources and abundant wildlife experts. We only have a small number of amphibian species. How good is our knowledge of their population sizes and trends? Even our presence/absence distribution maps are very variable in quality, and knowledge of populations is very patchy, even for the species that are of conservation concern, like natterjack toads and great crested newts.

Now consider Venezuela: a large country in political and economic turmoil with only a small number of dedicated herpetologists, but over 300 species of amphibians. The task of Red Listing here is immense and likely to be much based on educated guesswork. I have had some involvement over the last year in re-assessing the conservation status of Trinidad and Tobago’s much smaller number (35) of species, including three previously classed as threatened, and which share their ranges with Venezuela. The process has involved several herpetologists knowledgeable about the amphibians of the three territories pooling their information to complete the IUCN’s detailed evaluation forms, and coming to a judgement. The three species are:

  • Phytotriades auratus, the golden tree frog (see Figure). Formerly CR on the basis of occurrence only on two separate Trinidad mountain peaks, where it lives among the leaves and in the water tanks of huge arboreal bromeliads. Recent discoveries of populations in northern Venezuela and on another Trinidad mountain have led us to revise the assessment to EN.
  • Hyalinobatrachium orientale, the eastern glass frog (see Croaking Science, July 2020). Found along forest streams in northern Venezuela and in north east Tobago, but not Trinidad. Previously assessed as VU. Because of its limited range in Tobago and threats from deforestation in Venezuela, we retain VU as its Red List status.
  • Flectonotus fitzgeraldi, the dwarf marsupial tree frog (see Croaking Science October 2020). Found on forest and forest edge vegetation that holds pools of water, such as bromeliads and Heliconia, in northern Venezuela, Trinidad and Tobago. The previous assessment was EN, but when we examined the evidence, it became clear that this was a case where the previous assessors had made a judgment based on very limited data. Fortunately, we had been involved in extensive surveys of the presence/absence of this species in Trinidad and Tobago, as well as population estimates at a few locations. Added to data on the species’ range in Venezuela, we have been able to publish a paper (Smith et al. in press) and to assess this species as LC.

In these three cases, we have two reductions in the estimated threats. In both cases, these are not linked to active conservation effort, but rather to better data on the numbers and distribution of species. Much of the hard work has been done, not by experts, but by students and amateur naturalists taking part in actions like Bioblitzes. Mobilising citizens in this way has been important in the UK for taxa likes birds and butterflies. It needs to be done all over the world for more taxa.

References

Frost, D.R. (2020). Amphibian Species of the World, version 6.0. Available online.

Hanken, J. (1999). Why are there so many new amphibian species when amphibians are declining? Trends in Ecology and Evolution 14, 7-8.

IUCN (2001). IUCN Red List Categories and Criteria, version 3.1. Available online.

Smith, J. et al. (in press). The distribution and conservation status of the dwarf marsupial frog (Flectonotus fitzgeraldi; Anura, Hemiphractidae) in Trinidad, Tobago and Venezuela. Amphibian and Reptile Conservation.

Stuart, S. et al. (2004). Status and trends of amphibian declines and extinctions worldwide. Science 306, 1783-1786.

Croaking Science: More than meets the eye- cryptic frogs are more colourful than you think

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Mannophryne is a genus of 20 frog species found in the forests of Venezuela and Trinidad and Tobago. They belong to the family Aromobatidae, the sister family to the well-known Dendrobatidae, or poison dart frogs. Unlike poison dart frogs, that are brightly coloured to advertise their toxicity, aromobatids use cryptic colouration to blend into their surroundings as they do not have toxic compounds in their skins. In addition, they have a very effective escape response and can identify and reach cover quickly. This has led to one of their common names of rocket frogs, as well as being known as stream frogs, because of their normal habitat of stream margins.

In Trinidad and Tobago, we studied the endemic Mannophryne trinitatis (Trinidad) and M. olmonae (Tobago). Previous assessments of both species for IUCN indicated that they are threatened with extinction on account of habitat loss or degradation. An additional worry was the finding that both species were infected with chytrid fungus, the cause of numerous amphibian population declines across the world, although Mannophryne seemed not to suffer from the infection. We conducted population surveys of M. trinitatis in the Northern Range of Trinidad and found them to be numerous, no longer infected with chytrid, and with no sign of significant habitat loss. In Tobago, M. olmonae are very restricted in their distribution and are found at much lower numbers along streams in the northeast of the island. However, they also showed a lack of chytrid infection and no serious loss of habitat. We contributed to a review of IUCN’s frog assessments and recommend that M. trinitatis now be classed as Least Concern, and M. olmonae as Vulnerable.

Mannophryne are small mottled brown frogs, only a few centimetres in length, which are active during the day close to small mountain streams in primary and secondary forests. They feed on small  arthropods such as beetles, flies and spiders present on the abundant rotting fruit. During the rainy season (June to December), calling males can be heard morning and afternoon trying to attract a mate with their quick “weep, weep, weep” whistling calls. If you follow the calls and look carefully, they can be seen perched on rocks, roots, plants or at the mouths of small caves but will jump quickly away to safety if approached. Meanwhile, females hold a territory, which they defend from other females. When a female has chosen a mate, she follows the male into his cave and lays up to 14 eggs on the damp leaf litter. The males provide parental care, defending and cleaning the eggs until they hatch. This takes around 21 days and then each tadpole flips onto its father’s back and he begins the journey to look for a safe pool of water for his tadpoles to develop in. When a pool free from predatory fish or crustaceans and with a good supply of food is located, the father deposits some of the tadpoles and then searches for another. Tadpoles from a single clutch may be deposited in several bodies of water and will take around 2 months to develop to the stage of metamorphosis.

Figure 1: Calling male (left) and non-calling male (right) M. trinitatis.

One of the most interesting and recently studied aspects of this genus is their colouration. Sexual dichromatism is the difference in colouration between the males and females of a species. This is often used in communication as a visual signal to warn off competitors or highlight quality to potential mates. Sexual dichromatism can be split into two categories. Dynamic dichromatism only occurs in males and involves the development of temporary colouration, often as part of a courtship display, whilst ontogenetic dichromatism can occur in males or females and involves the development of a permanent colour difference as they mature.  Mannophryne are a very rare example among frogs in showing both, where males turn a jet-black colour when they call, and females develop a yellow patch on their throats as they mature.

This is noteworthy, because both forms of dichromatism are energetically expensive, stressing their importance. As male Mannophryne are active and calling during the day, their colour change seems counter- productive as it makes them more conspicuous. Additionally, it appears that open areas are a preferred calling site, and in turn attract a mate, further increasing their predation risk. Therefore, both signals (visual and audio) must be essential in attracting a mate. The role of the yellow throat in females is likely a signal of quality. We found that throat colour is individually variable in the extent of the colour patch and in its hue, ranging from pale yellow to bright orange. Larger and heavier females have more orange throats. Animals often use bright or bold colours to signal their quality to others and to avoid physical confrontation. In M. trinitatis, females can be see raising their heads to show their pulsing throat patch when confronted by another female. This signal shows that the defending female has the additional energy to dedicate to the “expensive” orange colouration and often provides enough incentive to dissuade the challenger from further conflict. Yellow and orange colours are based on carotenoid pigments, and there is evidence from many kinds of animals that carotenoids signal health and quality, as they are related to immune system functions. As a test of this idea that colour differences in the females are a sign of quality, we tested their escape responses in a semi-natural experiment: frogs with the brightest yellow throats showed more effective escape responses than the others.

Figure 2: Female (yellow throat) and male (grey throat) M. trinitatis

An extra facet to throat colour use by Mannophryne females  may be signalling their quality to males. As males take such exhaustive care of their clutch through to deposition of tadpoles, it is unlikely that they could manage more than one at a time. Therefore, it is important that they choose a high-quality female. Mate selection on both sides may be a more significant and understudied aspect to sexual selection in animals where males take all or the majority of parental care responsibilities.

Another fascinating piece of the puzzle is the timing of these colour changes. We observed the colour change on a male M. trinitatis, with the whole process taking around 20 minutes. The male was located by erratic calling and found to still be in its mottled brown colouration. As the calling became more consistent and frequent, the colouration changed to become darker until its change was complete. This is interesting because colour change in frogs is generally quite slow, mediated by hormones, and it will be interesting to discover if there is a special mechanism in Mannophryne. We found through rearing juveniles for several months after metamorphosis, that the yellow colouration develops very gradually in females, well before they reach sexual maturity.

Even though they do not have the bright colours or toxicity of their dart frog cousins, these little frogs are a lot more interesting and special than you might think at first glance.

Further Reading

Downie, J. R., Livingstone, S. R., & Cormack, J. R. (2001). Selection of tadpole deposition sites by male Trinidadian stream frogs, Mannophryne trinitatis (Dendrobatidae): an example of anti-predator behaviour. Herpetological Journal 11, 91-100.

Downie, J. R., Robinson, E., Linklater‐McLennan, R. J., Somerville, E., & Kamenos, N. (2005). Are there costs to extended larval transport in the Trinidadian stream frog, Mannophryne trinitatis (Dendrobatidae)?. Journal of Natural History 39, 2023-2034.

Greener, M. S., Hutton, E., Pollock, C. J., Wilson, A., Lam, C. Y., Nokhbatolfoghahai, M., … & Downie, J. R. (2020). Sexual dichromatism in the neotropical genus Mannophryne (Anura: Aromobatidae). PloS ONE 15(7), e0223080.

Greener, M. S., Shepherd, R., Hoskisson, P. A., Asmath, H., & Downie, J. R. (2017). How many Trinidad stream frogs (Mannophryne trinitatis) are there, and should they be regarded as vulnerable to extinction?. Herpetological Journal 27, 5-11.

Jowers, M. J., & Downie, J. R. (2005). Tadpole deposition behaviour in male stream frogs Mannophryne trinitatis (Anura: Dendrobatidae). Journal of Natural History 39, 3013-3027.

Lehtinen, R. M., Mannette, R. P., Naranjit, K. T., & Roach, A. C. (2007). Ecological observations on the critically endangered Tobago endemic frog Mannophryne olmonae. Applied Herpetology 4, 377-386.

Manzanilla, J., Jowers, M. J., La Marca, E., & García-París, M. (2007). Taxonomic reassessment of Mannophryne trinitatis (Anura: Dendrobatidae) with a description of a new species from Venezuela. Herpetological Journal 17, 31-42.

Contributing authors : Mark S. Greener and Roger Downie

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