It’s hardly a secret that I’ve had a bit of a thing going for frogs and toads – anurans – during the latter part of 2007 (the anuran series has so far consisted of part I, part II, part III, part IV, part V, part VI, and part VII). While the whole exercise was a good excuse to learn a lot about one of the most fascinating, charismatic and bizarre tetrapod groups, the main reason for going down this road in the first place is the major conservation effort that’s going to get underway next year.. or, tomorrow, if you’re reading this on New Year’s Eve. 2008 is, you see, the YEAR OF THE FROG: it’s nothing to do with the Chinese calendar, rather, it’s a concerted global effort to raise awareness of, and do something about, the Global Amphibian Crisis (GAC). What is the GAC, and what can we do about it?
There is no doubt among biologists that the world’s 6000-odd amphibian species are in trouble: about 1600 are classified as ‘threatened’, around 430 are listed as ‘critically endangered’, and at least 100 species – probably more than 160 – appear to have become extinct within the last couple of decades. This isn’t because amphibians are crap and hated by god, it’s because the results of our actions are killing them.
The Global Amphibian Crisis
Herpetologists first started noticing that things were going horribly wrong during the mid and late 1980s. First, populations and, later, entire species started disappearing. In Europe, large numbers of dead, diseased frogs were being found: the sorry corpses had open sores, were bleeding from their orifices, or were missing digits or feet (Pounds 1990, Langton 2002). Deformed frogs and salamanders, usually with missing or extra limbs, began to become commoner and more widely reported in the USA and elsewhere, and the number of cases sky-rocketed after 1995.
Among the lost are the Australian gastric-brooding frogs (Rheobatrachus) [female giving oral birth shown in adjacent image], the Costa Rican golden toad Ollotis periglenes [group of males shown in image at top], an estimated 67% of the 110 harlequin toad species (Atelopus), various of the Australian torrent frogs (Taudactylus), at least 18 Sri Lankan bubble-nest frogs (Philautus), Gunther’s streamlined frog Nannophrys guentheri and the Spiny-knee leaf frog Phrynomedusa fimbriata. Populations of common, widespread species, including the Northern leopard frog Lithobates pipiens and Western toad Anaxyrus boreas in North America and the Common frog Rana temporaria in Europe, have plummeted and suffered from numerous local extinctions. While the geological record shows us that extinction is a natural, ever-occurring process, the extinction rate we’re seeing among amphibians today appears higher than anything seen before, and even palaeoherpetologists familiar with the amphibian fossil record have gone on record stating that the extinction levels we are currently witnessing are not in the least bit normal (Delfino 2005, Stuart et al. 2005), and are unprecedented in terms of the geological record. It is not sensational to say that we are going to lose about half of all amphibians within the next five to ten years, unless major efforts are made. Given the role that amphibians play in global ecosystems, this is bad news to say the least.
What is causing the GAC?
Why are amphibians disappearing at such an alarming rate? While it’s clear that amphibians suffer from habitat loss, pollution and human exploitation, as do so many other living things, many of the disappearing species come from areas that actually haven’t been that badly affected, if at all, by obvious and immediate problems like deforestation. Instead it seems that amphibians are being hit in particular by several new problems.
Increasing numbers of debilitating deformities reported in North American, European and Asian frogs – usually involving extra or missing limbs – have recently been shown to result from infections of the trematode Ribeiroia (a parasitic flatworm). While trematodes like Ribeiroia have probably always been infecting frogs and other animals, the massive modern increase in infection is thought to be the direct consequence of aquatic eutrophication (elevated productivity), itself a result of fertiliser runoff and other forms of pollution (Johnson & Chase 2004, Johnson et al. 2003). Pdfs of pretty much all of the key papers on this subject are available free at Pieter Johnson’s site here [adjacent image depicts the complex life cycle of Ribeiroia, borrowed from greenmuseum.org].
A second problem is more widespread and more destructive: it is chytridiomycosis, an infection caused by the fungus Batrachochytrium dendrobatidis. B. dendrobatidis is widely called chytrid fungus, but some experts have argued that this term is misleading because it refers to an entire family of fungi and not just to the one problem species: as a consequence, it has been recommended that it is better known simply as ‘Bd’. Bd attacks amphibian epidermal cells, in its infective stage is free-swimming and flagellated, and it seems to require keratinized skin to grow (in tadpoles for example it only grows on the mouthparts). We know that at least some salamanders are killed by Bd, whereas others can carry it but apparently don’t express symptoms. It has been reported in captive caecilians, but we don’t yet know whether it affects wild ones. Certainly in the majority of metamorphosed anurans it is fatal: within a year, about 80% of the anurans in an affected area will die. It is thought that most – perhaps nearly all – recently extinct amphibian species owe their disappearance to Bd. Its spread can’t really be prevented in the wild, and consequently several efforts have been made to capture wild frogs in threatened areas, and to then maintain them in captivity.
Why is Bd such a problem when it apparently hasn’t bothered amphibians before? Firstly, it now seems that Bd was originally endemic to southern Africa where it infected Xenopus laevis, the African clawed frog (Ouellet et al. 2005, Blaustein & Dobson 2006). This is the species that has been taken all over the world due to its use in pregnancy testing, and just about everywhere it’s been taken it has escaped, taking Bd with it: today, Xenopus is feral and breeding in Europe, the USA, Chile and doubtless in loads of other places. Another carrier species which has been widely introduced all over the place is the American bullfrog Lithobates catesbeianus.
That’s not the only cause of the problem however: contrary to initial suspicions that Bd is most lethal to hosts at low temperatures, a major recent study of frog decline across South America showed that large-scale climatic warming and increased cloud cover resulting from particulate air pollution have shifted average temperatures at mid elevations (where amphibian diversity is highest) closer to those that are the optimum for Bd (Pounds et al. 2006). We therefore have a very worrying combination: spreading pathogens assisted by changing climates. An excellent review of recent discoveries about Bd were provided by Carel at Rigor Vitae: essential reading if you want to get up-to-speed on the GAC.
Why does the GAC matter?
It now seems cliché to refer to amphibians as the canaries in the coal mine, but it is looking increasingly likely that this is the case. Ribeiroia and Bd have become a problem due to changes caused by us, and it now seems that several other parasites of cool and cold climates have modified their life cycles as conditions have warmed, with studies suggesting that detrimental effects on the fecundity and health of various species (including Musk ox Ovibos moschatus and Rocky Mountain pine trees) will result. Because of their (generally) permeable skins, amphibians have proved important in terms of alerting us to problems caused by the absorption of certain herbicides and other chemicals. So amphibians are quite probably the blinking warning light that we really need to pay attention to [adjacent image shows multi-legged ranid frog from China].
The decline of amphibians worldwide is sad, if only because – as I’ve tried to showcase here at Tet Zoo – they’re remarkable, amazing to look at, and really, really interesting. The world will be the poorer without them, as will we. But this group of animals is also integral to the way many ecosystems function, and the decline and loss of so many species is – if you’ll excuse another cliché – equivalent to losing lots of rivets from the airplane we’re all flying in. Amphibians are an important resource for many other other animals, and they are also significant predators of insects and other invertebrates, some of which are important pests.
I’m not personally a fan of the idea that organisms are only worth saving when they’re utilitarian, but there are indications that the extinction of amphibian species might prove to be a serious loss to human health and welfare. Of 14 skin compounds collected from wild frogs in 2005, for example, three were shown to inhibit HIV infection in humans (VanCompernolle et al. 2005: free pdf here). Epibatidine – a chemical produced by highly toxic South American poison-arrow frogs – has recently been isolated and used in the production of a painkiller which is about 200 times more powerful than morphine, yet lacks the latter’s addictive and toxic side effects. It’s likely that we’ve already lost a lot of potentially useful information: it’s been speculated, for example, that the gastrointestinal biology of the two gastric-brooding frogs might have taught us how to combat ulcers and gastrointestinal cancer, but both species became extinct before we really got to study them.
So what can be done?
In 2008, lots of people are participating in an effort to do what can be done. There are perhaps about 500 amphibian species that are in such danger of extinction that there is almost certainly not enough time to conserve them in the wild; they can only be saved if we maintain them in captivity. And so the IUCN Amphibian Specialist Group Conservation division has set up the Amphibian Ark project. Working in association with zoos, botanical gardens and aquariums all around the world, the aim is to raise $50-$60 million in order to save these 500 species: that sounds like a lot of money, but it works out at $100,000 per species, which is actually incredibly cheap. In theory, a wealthy individual or a company, for example, might single-handedly save a species from extinction.
Essentially, the easiest way we can all help is by increasing awareness of the GAC and the Amphibian Ark project. So I urge all bloggers interested in conservation, science, nature and biology to help spread the word and become part of this important movement.
— Visit the Amphibian Ark website and help publicise it (http://www.amphibianark.org/). The more individuals, schools, teachers, local societies and conservation groups that get involved, the better, so if you can help by bringing Amphibian Ark to their attention, that’s great.
— Check out the Amphibian Ark’s official blog, Jeff Davis’ Frog Matters.
— Sponsors are needed, so any help in getting environmentally-aware companies involved would be awesome. The first company to offer corporate sponsorship was Clorox, a bleach manufacturer. If you’re wondering how bleach relates to amphibian conservation, the answer can be found here on Frog Matters. You don’t have to be a big company to offer financial help: donations can be made through paypal on the Amphibian Ark website here.
— Help by signing the online petition: it is hoped that this will be the biggest petition in history, and will convince governments around the world to do more to help (the petition takes less than 20 seconds to sign and submit). Tet Zoo has at least a couple of thousand regular visitors: I urge you all to sign the petition – it will make a difference.
— An information pack is available for zoos, aquariums and other institutions that want to be part of the event and organize activities and displays. Merchandize is also available.
Early in 2008, David Attenborough’s last television series, Life in Cold Blood, will air, and it will also help raise awareness of the GAC. Indeed Sir David attended the unveiling of a special sculpture at London Zoo to help promote Amphibian Ark’s Year of the Frog, has signed the online petition, and has provided a special message promoting Year of the Frog.
So there we have it. We will definitely see an awful lot on amphibian conservation and the Amphibian Ark project in 2008 and beyond, and Tet Zoo will remain involved throughout. I will leave you with an excellent talk on the GAC and Amphibian Ark project given by Kevin Zippel, Amphibian Ark’s program officer…
Refs – –
Delfino, M. 2005. The past and future of extant amphibians. Science 308, 49-50.
Johnson, P. T. J. & Chase, J. M. 2004. Parasites in the food web: linking amphibian malformations and aquatic eutrophication. Ecology Letters 7, 521-526.
– ., Lunde, K. B., Zelmer, D. A. & Werner, J. K. 2003. Limb deformities as an emerging parasitic disease in amphibians: evidence from museum specimens and resurvey data. Conservation Biology 17, 1724-1737.
Langton, T. 2002. On the trail of a serial killer. BBC Wildlife 20 (2), 56-60.
Ouellet, M., Mikaelian, I., Pauli, B. D., Rodrigue, J. & Green, D. M. 2005. Historical evidence of widespread chytrid infection in North American amphibian populations. Conservation Biology 19, 1431-1440.
Pounds, J. A. 1990. Disappearing gold. BBC Wildlife 8 (12), 812-817.
– ., Bustamante, M. R., Coloma, L. A., Consuegra, J. A., Fogden, M. P. L., Foster, P. N., La Marca, E., Masters, K. L., Merino-Viteri, A., Puschendorf, R., Ron, S. R., Sánchez-Azofeifa, G. A., Still, C. J. & Young, B. E. 2006. Widespread amphibian extinctions from epidemic disease driven by global warming. Nature 439, 161-167.
Stuart, S. N., Chanson, J. S., Cox, N. A., Young, B. E., Rodrigues, A. S. L., Fischman, D. L. & Waller, R. W. 2005. The past and future of extant amphibians: Response. Science 308, 50.
VanCompernolle, S. E., Taylor, R. J., Oswald-Richter, K., Jiang, J., Youree, B. E., Bowie, J. H., Tyler, M. J., Conlon, J. M., Wade, D., Aiken, C., Dermody, T. S., KewalRamani, V. N., Rollins-Smith, L. A. Unutmaz, D. 2005. Antimicrobial peptides from amphibian skin potently inhibit human immunodeficiency virus infection and transfer of virus from dendritic cells to T cells. Journal of Virology 79, 11598-11606.