Reintroducing Endangered Species Often Dangerous
Amphibian Chytridiomycosis and Genetic Diversity Facts
Sep 7, 2009
It might seem like a good idea to reintroduce endangered animals to their natural habitat from breeding programs, but there are often hidden problems.
Genetic Diversity of Captive Amphibians
Pet amphibians, or those bred for research purposes, come originally from small ‘founder’ stocks. There might well be many varieties available, but the ‘wild-type’ (those that would be likely to survive in their natural habitat) usually have very little genetic diversity.
Genetic Problems When Releasing Amphibians
- Endangered species are, by definition, not abundant in the wild.
- Released animals (if they survive in large enough numbers) will effectively take over as the ‘wild’ animal.
- The original genetic diversity of the wild population will be heavily diluted and maybe even lost.
- This is serious because a species only has a long-term evolutionary future when the population carries sufficient diversity to allow adaptation to changing environment.
Fungal disease (chytridiomycosis) is killing amphibians all over the world at an alarming rate. The fungus damages the skin and is often noticeable as a reddish tinge on the belly.
Chytridiomycosis is a relatively recent problem, and it is now thought to have become widespread with the help of the African Clawed Frog. These frogs were bred all over the world from the 1930s onwards.
African Clawed Frogs
The African Clawed Frog (Xenopus laevis) was used in the middle of the last century for pregnancy testing. (If female frogs are injected with urine from a pregnant woman they rapidly produce eggs.)
They also have large tough embryos that have been widely used for developmental biology research.
African Clawed Frogs are immune to Batrachochytrium dendrobatidis (the cause of Chytridiomycosis) which was originally only found in the frog’s native African habitat.
Escaped pets and research animals, as well as deliberate introductions, have now established this frog in wild habitats around the world. They have passed on the fungus to many other amphibians (without natural immunity), with devastating consequences. They also tend to eat native species!
Dangers of Axolotl Reintroduction
It might be tempting to increase the numbers of axolotls in their wild habitat (axolotls are almost extinct in the wild) by introducing captive-bred specimens. Pet and research axolotls are plentiful, but reintroduction might cause permanent damage to the wild population.
It is not known exactly how many axolotls survive in the wild – their extremely small habitat suggests very few – but it is almost certain that the population is genetically distinct from captive-bred animals. If large numbers were to be reintroduced into the remnants of Lake Xochimilco, their only habitat, the wild animal would not be saved, rather the pet animal would replace it.
An additional problem is the possibility of releasing the fungus (Batrachochytrium dendrobatidis) into the water, and this would probably wipe them all out.
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