ECOS 38 (4)

Amphibians are the most threatened species of vertebrates but are we doing enough to conserve them? Ex-situ breeding programs for amphibians are now starting through Amphibian Ark, but could we be doing more?

Discovery, threats, extinctions…

Amphibians are the most threatened group of vertebrates with approximately 41% of species currently threatened with extinction. Those that have the highest risk of extinction often have ex-situ breeding programs set up so that an insurance population can be founded from which individuals can be bred ready for release. This has worked well for some species such as the mountain chicken (Leptodactylus fallax) found on Dominica and Monserrat. Without the intervention of Zoological Society of London (ZSL) and other partners the species would almost certainly be extinct by now.1 This high rate of extinction is confounded by the high rate at which new species are discovered, with approximately 140 new amphibian species, especially frogs, discovered each year. The Red List assessments for these species can be Data Deficient which means that insufficient information if available to make a correct judgement regarding the assessment. This happens frequently with newly discovered species as the information available is limited compared to species we’ve known about for a while.

The Global Amphibian Assessment (GAA) was carried out in 2004 and found that 32% of species were threatened with extinction. Since then, this figure has slowly been creeping up as we’ve learned more about the threats that face amphibians and as new species have been discovered or assessed. Some of the biggest threats include disease, habitat loss and pollution.2 We still do not fully understand all of the factors affecting amphibian populations but we know that they are currently being hit by the synergistic effects of a number of threats which are effectively hitting them whilst they are already down. For example, their immune systems may be suppressed due to pollution and then disease is introduced into the area (perhaps through an introduced species), this then infects the amphibians and unfortunately causes the population to decline. This outcome has been observed all over the world but was first noticed in Australia and central America in the 1970s and 80s.

 

A mountain chicken from Rotterdam Zoo, here the frogs are used to educate visitors on their plight as opposed to the captive breeding program seen elsewhere.

Photo: Steve Allain

Husbandry of emerging species

Since the time of the GAA hundreds of new species have been discovered thanks to advancing molecular techniques and a better understanding of taxonomy. With these new species also come new problems. The husbandry of these new species often isn’t well known and so if a captive insurance population is established, not only does it have to be biosecure but the correct environmental set-up needs to be replicated so that the species can breed and contribute towards the survival of their species. This can often take time and with the loss of valuable individuals from a genetic standpoint it can be a risky game to play. Fortunately the husbandry of captive amphibian populations has come a long way in the past 20 years and these risks however still present, have been minimised. Due to these various practical problems not every endangered amphibian species meets the requirements for a captive breeding program.

There are a number of factors preventing the successful captive breeding of certain amphibian species. The first is that not all species which are threatened with extinction are suitable for captive breeding. To maintain a viable insurance population takes a huge investment of time and money which isn’t always available. Amphibian Ark is the coordinating partnership for endangered amphibian captive breeding programs. It has partners mainly in Europe and North America. There may be difficulties in procuring the correct licenses to export animals from the countries where threatened amphibians live due to political boundaries. As it currently stands, less than 10% of threatened amphibian species are held within zoos and other institutions. This figure has steadily increased in recent years but it is still not enough to stave of extinction.

Improving captive breeding programs

Another issue that underpins the success of ex-situ programs is the level of expertise in the native countries of these species. Again the case of the mountain chicken can be used here as ZSL has tirelessly helped to educate the local people of Dominica about the importance of the species. ZSL has built a captive breeding facility on the island and trained local people who now work at the centre. It is important to consider capacity building (helping to improve local people’s skills and confidence) as part of a captive breeding program. Post-release monitoring will need to be carried out and once the program is complete and the institutions involved leave an area, the survival of that species will likely fall back into the hands of the local people. If they aren’t aware of the threats, the basic biology and survey methods then it’s likely that more help and intervention will be needed in the future.

Zoos have to balance the visitor experience with conservation. This is much easier for charismatic species such as tigers and elephants, but is much harder to achieve with amphibian species. The displays of many amphibian species may be attractive to the eye, and the animals within them can be harder to spot than you’d first expect. This may be due to camouflaged colouration and the slow and subtle behaviour. This cryptic nature of amphibians can make them less attractive exhibits even though they take up a fraction of the space a typical mammal species does. Zoos with limited expertise in the keeping and husbandry of amphibians will likely stick with easier, better established species of which the requirements are well documented.

The Lake Oku clawed frog (Xenopus longipes), a critically endangered species which ZSL has successfully bred in captivity for the first time which has a similar story to the mountain chicken.

Photo: Steve Allain

Lingering threats of failure

One of the biggest threats to amphibians currently is the amphibian chytrid fungus (Batrachochytrium dendrobatidis) which causes the thickening of keratin within amphibian skin. This then interferes with electrolyte homeostasis and fluid balances. It is believed that the eventual cause of death from the disease is cardiac arrest due to the loss of control in these systems. Infection is almost certainly fatal for most species although there are a number within temperate zones which seem to be immune (such as the common frog and American bullfrog). There is no known cure to the disease at present although some trials have previously shown promising results. Chytrid fungus is environmentally resilient. This means that even after a species has been extirpated from an area, the fungus may still be lingering in the environment. This means that until it can be proven that the threat of the fungus returning is minimal, the captive bred animals can’t be released and will have to remain at the facilities where they were bred. This of course means increased upkeep costs in terms of space, food, lighting and heating.

Reaching for the Ark

Captive breeding and subsequent reintroduction programs are trickier than they first seem. They take much effort from a number of organisations and stakeholders to help make them a success. They have been assessed in detail in the past but more can still be done to ensure the survival of an ecologically important group of animals.3 The captive breeding of amphibians for conservation purposes has come a long way in the past 10 years but there is still a lot more that could be done. As we’ve seen, these problems are not the easiest to overcome. Hopefully Target 12 of the Aichi Biodiversity Targets will help increase the level of international cooperation in saving species of amphibians on the brink of extinction. It states that “By 2020 the extinction of known threatened species has been prevented”. We can only cross our fingers and hope that within the next three years that a number of other amphibian species find their way both onto the Ark and on their way to recovery.

References

  1. Tapley, B., Harding, L., Sulton, M., Durand, S., Burton. M., Spencer, J., Thomas, R., Douglas, T., Andre, J., Winston, R. & George, M. (2014). An overview of current efforts to conserve the critically endangered mountain chicken (Leptodactylus fallax) on Dominica. The Herpetological Bulletin 128, 9-11.
  2. Wake, D. B. & Vredenburg, V. T. (2008). Are we in the midst of the sixth mass extinction? A view from the world of amphibians. Proceedings of the National Academy of Sciences 105, 11466-11473.
  3. Dawson, J., Patel, F., Griffiths, R. A. & Young, R. P. (2016). Assessing the global zoo response to the amphibian crisis through 20‐year trends in captive collections. Conservation Biology 30, 82-91.

Steven Allain

The author is an Anglia Ruskin graduate in Zoology with a passion for amphibians. He is a member of the Amphibian Specialist Group and has worked on writing Red List assessments for the amphibians of south-east Asia where he carries out some of his research.

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