Zoology

Why Amphibians are Unique in the Animal World



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Amphibians may be small and diverse vertebrates, living on the land or sea, but they are ultra sensitive to environmental change. That makes them unique among animals. Their whole lifecycle from larvae, to unshelled eggs, to their very skin sensitively exposes them to every whim of the atmosphere, natural or man-made. They could be our "secret prophets" of future worlds.

Few animals can live on both land and sea. Amphibians are a unique animal that can metamorphose from an aquatic animal with gills to a terrestrial, cold-blooded animal with lungs (except the lungless salamander). But that uniqueness doesn't stop there. You would think this ability would give amphibians an edge on life. But it is a knife edge. "More than 160 species of amphibians may already be extinct. More than 1,800 amphibian species are threatened with extinction that's 32% of all known amphibian species." www.stlzoo.org Frogs, perhaps the most "common", well-known amphibians are becoming extinct. Why? Is this a sign of a "deadly" world on the horizon?

Air, tainted with greenhouse gases, or water, polluted with heavy metals, pesticides or herbicides at best deforms amphibians, in particular, frog populations. Their thin, moist, permeable skin helps them breathe. So the air passes through every part of their body. It is easy to see how this animal is highly susceptible to any changes in atmosphere. "In 1995, Blaustein and Wake observed that many threatened amphibian species lay their jelly-like egg masses in open, shallow waters at high altitudes. They proposed that increased UVB radiation coming through a thinning stratospheric ozone layer was making the amphibians' eggs more susceptible to fungal infection." www.aveweb.org Strangely, only the poison arrow frogs appear to be adopting UVB avoidance behavior. And at lower altitudes, cases of deformed amphibians have been recorded in southern Quebec, where pesticides were used heavily in potato and sweet corn farming.

Amphibians are unique animals because they have initiated a world panic to protect them. In 2006, "a coalition of zoos, aquariums, and botanical gardens announced a $400 million drive to establish captive breeding programs for the most threatened species. The effort, dubbed the Amphibian Ark, seeks to house 500 individual frogs from each of 500 species in biosecure facilities around the world." www.news.mongabay.com

But frogs are not the only amphibians. In fact, there are more than 5,500 species including frogs, bullfrogs, toads, salamanders and caecilians. And they too are presenting alarming trends of extinction.

In 1998, 200 tiger salamander carcasses littered the shoreline and lake bottom of Lake Desolation in Utah. Those still alive swam in circles and could not stay upright. Red spots and swollen areas on the skin were noted. There was bleeding beneath the skin. The phenomena could only be explained as a virus. Yet the same phenomena had also been reported earlier in the year in Maine and North Dakota. Is the salamander virus another dimension of the frog crisis?

Salamanders are especially unique, even in the amphibian world. Some are entirely aquatic, never developing air breathing lungs; some are entirely terrestrial in adult life; some dabble between the two. They can even re-generate lost limbs. Many scientists claim it is the salamander that should be closely monitored. They are sensitive to forest management practices and stream water quality. The real health of a forest, (such as in the southern Appalachians), and stream is reflected in the health of the resident salamander.

Caecilians are the wormy amphibians with backbones. They are almost blind and their skin looks like the scales of a fish. But their claim to unusual features is based on their behavior. They dig with their heads. Little is known of the lifecycle of this amphibian, but could they be useful too, monitoring and testing soil quality?

Amphibians can claim to be the very first vertebrates to live on land. Critical environmental circumstances may honour amphibians with the key to the future of humanity. Indeed, amphibians are unique animals.

Sources
www.aveweb.org
www.nationalzoo.si.edu
www.mongabay.com
www.sciencedaily.com

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