May 23, 2008

The Amphibian Ark: Good Intentions, Uncertain Outcomes

The Amphibian Ark is a conservation effort developed to implement the ex situ (i.e., captive breeding) components of the IUCN Amphibian Conservation Action Plan (ACAP). The mission of the Amphibian Ark is to "ensure long-term survival of species in nature utilizing short-term ex situ management of amphibian taxa for which adequate protection in the wild is not currently possible". Although it is very unfortunate that adequate protection in the wild is in fact no longer possible for an increasing number of amphibian species, this is a reality of our time. The recent global emergence of the amphibian chytrid fungus (Batrachochytrium dendrobatidis) has massively compounded this problem, and was a major impetus for the development of the ACAP.

The fact that many amphibian species are being driven to extinction is irrefutable. What actions will be most effective in preventing these extinctions remains very much an open question. The ACAP suggested a very important role for captive breeding, but is captive breeding a realistic solution? Hundreds of amphibian species are being driven to extinction by a myriad of factors including disease, habitat destruction, introduced species, and overharvest. Do we really have the resources to harbor even a fraction of these declining amphibian species in captivity? The ACAP provides some insights into the costs of captive breeding programs, and these figures are an eye-opener. The estimated 5-year cost to house 100 amphibian species in zoos is $41,000,000! Where is this money going to come from? Will it be siphoned away from already-scarce funds used for conservation efforts currently being implemented in the wild?

The idea of housing hundreds of species in zoos brings with it difficult issues that go well beyond financial considerations. One of the most important is what the fate of those captive populations will be. For species threatened primarily by habitat destruction, efforts at preserving pieces of habitat could be followed by release of animals back into the wild. However, the fact that disease is playing such an important role in causing global amphibian declines greatly complicates the role of captive breeding. For example, the amphibian chytrid fungus is spreading around the world, and once it is present at a site it is apparently there forever. Under this scenario, releasing disease-free animals back into the wild will not be an effective conservation strategy. The released populations will simply become reinfected and succumb. Numerous examples from the field of disease ecology indicate that the only solution to the effects of disease is evolution between host and pathogen. Putting amphibians into zoos and keeping them free of disease will halt the process of host-pathogen evolution, and will ensure that the captive populations will not have a chance of survival in the wild.

Another serious concern related to captive breeding is the unavoidable genetic effects on the captive population. These effects arise from the novel environment in which the animals are held, which will always be markedly different from that in the wild. These changes to the environment induce new selective pressures that can result in rapid changes to the animals themselves. A recent article published in the journal, Science, showed that steelhead trout raised in hatcheries had greatly reduced reproductive capabilities when released back into the wild. The reduction in reproductive capabilities accrued at the astounding rate of 40% per generation, so every generation had approximately half the reproductive capability of the previous generation. Based on these striking results, the authors concluded that "even a few generations of domestication may have negative effects on natural reproduction in the wild" and that "the repeated use of captive-reared parents to supplement wild populations should be carefully reconsidered".

There are no easy answers here, but there sure are enough difficult questions to give me pause when contemplating the role of captive breeding programs for hundreds of the world's amphibian species.

Back to The Mountain Yellow-legged Frog Site.

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