Saturday, 12 March 2011

Frogs of Bristol 1: The Golden Mantella

A recent piece of research into which animals visitors to zoos pay most attention to rated amphibians as next after mammals (especially primates) in popularity. Just over a year ago, Bristol opened its ‘Amphipod’ – a climate controlled timber exhibit with two modest sized rooms for breeding endangered amphibians. Most people reading this blog will be aware of the global amphibian crisis caused by chytrid fungus, so I will not repeat that. I would like to talk instead about the various amphibians we have at Bristol and their current situation in the wild.

The Amphipod was designed to provide biosecure breeding facilities for at-risk amphibians, and few are more so than the Critically Endangered, tiny (2cm) Golden Mantella, Mantella aurantiaca. One of at least 16 species of Mantella (there are probably several more undescribed forms), it is confined in the wild to perhaps as little as 10km2 of primary and secondary rainforest in east central Madagascar at a fairly high altitude. The habitat is basically a collection of forest fragments, all threatened by logging for firewood and forest fires, although their preference for marshy areas provides a little protection from those.

Amphibians as a group have some of the greatest diversity in reproductive strategies of any vertebrate, and this makes breeding them in captivity a challenge until their breeding behaviour is understood. Mantellas are terrestrial breeders, laying eggs in wet moss at the edge of water and allowing rain to wash tadpoles into the water where they develop. For Golden Mantellas at least, their breeding is opportunistic, and breeding takes place whenever the conditions are right. Some other amphibians have far more complicated triggers to breeding - I have heard of one Caribbean species that reproduces only on one or two nights a year, triggered by the first full moon of the rainy season.

In the Amphipod, conditions can be modified so that they can be bred at will, and from a starting group of 38 adults we have produced over 500 tadpoles and froglets in 12 months. Most of these have since been distributed to other collections in Europe. The tadpoles develop in the same way as for more familiar species, but the newly metamorphosed froglets are only a few millimetres long, so feeding them is a problem. Adults will take fruit flies and pinhead crickets, but the new froglets require even smaller prey, so they are fed on springtails. It takes several months before they develop the bright orange warning colours of the adults.

The adult frogs are kept in all glass vivaria for ease of cleaning. A sloping glass land surface, covered with live sphagnum moss, with a potted plant for climbing is all they require. A plumbed-in mister allows the adults to be sprayed with chemical-free water daily, and the lighting is a full spectrum fluorescent lamp. It is important that amphibians receive UV lighting, as infertility or disease results if they do not, but it is vital they do not overheat. Amphibians are extremely prone to heat stress, and before the Amphipod was built we had no luck breeding Mantellas during the summer, even in the UK, as it became too warm for them.

In the post I made a short while ago on Asiatic Lions (our cubs are doing nicely by the way), I mentioned the problems of maintaining captive populations of sufficient size to be viable. With animals the size of most amphibians, this is less of an issue, as the vast majority are extremely small. To maintain a viable population of say 2000 mantellas, you would require about twice the space of the average sized living room, which is at least theoretically manageable. Even the largest of the frogs and toads could easily be saved, so long as sufficient space for their often peculiar lifestyles was available.

For a video of Golden Mantellas in the wild, see here:

Next week, Lemur Leaf Frogs – the other inhabitants of the Amphipod

No comments:

Post a Comment