Sunday, May 28, 2000		Nature

Deadly tales
By Nutan Shukla

SOUTH American arrow-poison frogs are carriers of deadly toxins, but at the same time their males are highly caring fathers too. Both the sexes of these creatures have toxic skins, consequently they have no need to hide from predators. They can be easily seen roaming about on the forest floor boldly advertising their bright colours, but their young ones are brownish black and do not have any poison.

Their tadpoles are very vulnerable since they do not have any defence mechanism, the male arrow-poison frog stands guard over the eggs laid by his mate on a leaf or on a patch of ground that has been cleared by both of them. Once the tadpoles have hatched, they wriggle onto their father’s back. Here they become securely attached by a thick, sticky mucus. The father carries his offspring to a nearby pool, where the mucus dissolves and frees them to complete their development.

These caring parents are very dangerous to other animals. We all know of the dramatic effects of the venoms of snakes and spiders, the savage stings of wasps and jellyfish and the virulent poisons of scorpions and stingrays, but these beautiful, brightly coloured and highly attractive amphibians are even more lethal.

The champion poisoners — the Borgias of the forest — are the tiny kokoi frogs that patter boldly about in the tropical undergrowth of South America. These creatures, usually less than 2 inches long, carry in their skin-glands a poison so powerful that it is hard to describe its strength. If you collected as little as 1gram of this toxin, it would be enough to kill a hundred thousand average-sized men. One ounce is enough to wipe out more than two-and-a-half million people. It is the most potent poison known to human beings from the entire animal world.

These amphibians have been given the name of arrow-poison frog because long before white men arrived on the scene, the local Indians living deep in the Amazonian rain forests caught and killed these animals to provide themselves with poison tips for their arrows. Impaled on a stick and held over a fire, the dying frogs exuded a milky secretion. The arrows were held in this liquid and then allowed to dry. One frog was used to coal fifty arrowheads. When the Indians went hunting, whether for animals or for rival Indians, their firepower was deadly. Anything struck by a poisoned arrow was paralysed almost immediately and in few moments was dead.

Because of their lethal defence system, arrow poison frogs are able to live untroubled lives on the forest floor, hopping about conspicuously with bright colours advertising their presence. Many other animals that harbour secret chemical defences also show themselves fearlessly to the world and some of them also perform special displays that indicate their readiness to engage in a chemical encounter.

Males of African bullfrogs look after their eggs and tadpoles in a manner that suggests considerable foresight. Bullfrogs breed and deposit their spawn in temporary pools and puddles created by heavy, though sporadic, summer rains.

In warm weather these pools quickly shrink, leaving developing tadpoles stranded in tiny puddles around pool rims. If the puddles dry up completely, the tadpoles will die. But the squat, heavily built males, up to 9 inches long, appear to be well prepared for this danger. As their broods become isolated by the evaporating water supply, they set to works digging escape channels with their powerful hind legs. In this way they create tiny canals that allow the tadpoles to swim back to the safety of the main pool.

The female Australian pouched frog lays her eggs on damp leaves or moss and then abandons them. The male, however, returns when the eggs are due to hatch, and by dint of nudging and pushing the tadpoles, stimulates them to wriggle into the pouchs on either side of his body. There they develop, well protected beneath his poisonous skin, until they are ready to emerge as tiny frogs.