Thursday, May 5, 2011

Golden Toad ( Bufo periglenes)

The disappearance of the golden toad was both mysterious and rapid. Only 25 years separate the species’ discovery by scientists in 1964 and the last sighting in 1989. Since its disappearance, this 5-cm-long toad has become an icon for the decline of amphibians the world over.

Unlike the majority of toad species, the male golden toad was brightly colored and shiny to the extent that it looked artifi  cial. The species was also unusual as the male and female were very diff  erent in appearance. The male, with his magnifi  cent golden orange skin, was in stark contrast to the larger female, who was black with scarlet blotches edged in yellow.

This toad was only known from a small area (around 10 km 2 ) of high-altitude cloud forest in Costa Rica that today is part of the Monteverde Cloud Forest Reserve. These forests Golden Toad The golden toad was restricted to the loud forest above the city of Monteverde in Costa Rica. It was last seen in 1989. (Renata Cunha)(also known as elfi  n forests) are characterized by cloud, epiphytic plants galore, and small trees, which all in all give them a very primeval feel. In this small area of perpetually moist forest, the golden toad could apparently be encountered commonly and in large numbers, but only during the breeding season. The breeding season extended from April to June, when the rainy season is usually at its most intense. These rains would fill the hollows around the bases of trees and other natural depressions with water—ideal toad breeding pools. The toads would collect around these pools in great numbers with the sole intention of breeding. Mating in any toad species is far from genteel, and golden toad breeding was a free for all. The males outnumbered the females by eight to one, and any female in the vicinity of a breeding pool soon found herself beneath a writhing mound of potential suitors. The males would get so excited and desperate that they would try to mate with anything that moved, including other males. Occasionally, between 4 and 10 feverish males would grab hold of each other to form a toad ball the signifi  cance of which is unknown—perhaps a female was in the middle of the ball but managed to give her suitors the slip. Once a male had struggled with his competitors and beaten them to get a good hold of a female in the breeding grasp known as amplexus, he could fertilize her eggs—or at least, this was his intention. Often, other males would come along and try to separate the mating couple so that they could get a chance at fertilizing the female’s eggs.

What with all this wrestling and bad sportsmanship, it’s quite surprising that the golden toad managed to breed at all, but breed they did, and the female would eventually lay 200–400 3-mm eggs in a long string in the breeding pool. Compared with many species of toad, the golden toad laid relatively few big, yolk-packed eggs, rather than lots of small ones, and it is thought this breeding strategy evolved because of the small size of the pools on which the toad depended. These pools didn’t last very long, and so after the tadpole hatched, the race was on to change into a toadlet as quickly as possible. The abundant yolk in the eggs was the fuel for this rapid development.

After hatching, the tadpoles would spend around fi  ve weeks in the ephemeral pools before they lost their tadpole features and sprouted limbs, enabling them to begin their life on land. What the toads did outside of the breeding season is unknown. We don’t know what food they ate and how they went about catching it. The adults of the majority of other toad species are pretty unfussy when it comes to food, and they go for just about any creature that will fi  t inside their capacious mouth. There is no reason to believe the golden toad was any diff  erent, but its small size restricted it to small animals like insects and other invertebrates.

Like much of the golden toad’s biology, we also have a poor understanding of why it disappeared. We know that when it was fi  rst discovered by Western scientists in 1964, it was found in large numbers, but in a very small area. In 1987, 1,500 adults were seen, but then in both 1988 and 1989, only one adult was seen. What happened to cause such a massive population crash? We don’t know for sure, but there are three main theories. It has been suggested that as the toad had such special breeding requirements—short-lived pools and a narrow window of opportunity—one erratic year of weather conditions would have completely scuppered their chance of a successful breeding season. Species like the golden toad have very specific habitat requirements, occupying very small ranges. This predisposes them to extinction as one little change in their environment can leave them with nowhere to go. Other scientists have suggested increasing amounts of ultraviolet (UV) radiation penetrating the atmosphere could have harmed the toads, but as they lived in dense forest shrouded in cloud during the breeding season, this is unlikely to be the cause of their demise. The last theory concerns the spread of chytrid fungi, which appear to make short work of amphibian populations wherever they become established. Drier conditions could have forced the toads into fewer and fewer ponds, increasing the transmission of this disease. With this said, it is possible that the golden toad still clings to existence in some remote corner of Central America.

Source: Wikipedia


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