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Asian Treefrogs: Rhacophoridae - Behavior And Reproduction

eggs species water male

The Asian treefrogs are perhaps best known for three reasons: Some can glide through the air; some are poisonous; and some build foam nests. Although they are often called flying frogs, they can actually only glide. In other words, they cannot flap their legs to go higher in the air as a bird can with its wings, but they are able to soar from tree to tree. They do this by stretching out the webbing between their toes into a fan shape and using these large web-fans to catch the air and prevent them from falling too quickly. To glide, the frog typically reaches out in a Superman-like pose, but with the legs slightly bent. They adjust the angle of their feet to change direction in flight. Wallace's flying frog is an excellent glider. When this frog leaps from a height of 17.7 feet (7.3 meters), it can soar through the air for a distance of up to 24 feet (7.3 meters). Other gliding frogs include such species as the jade treefrog and the Himalaya flying frog. Besides being a quick way to get around the forest, gliding helps the frogs escape predators that cannot soar or fly.

The poisonous members of this family are called mantellas. Like the poison frogs of South and Central America, they have poison in their skin. Most of the other members of this family are active at night, which helps hide them from would-be predators. The mantellas, on the other hand, are not only active in the daytime, but they also sit right out in the open. Their bright colors draw even more attention to them. The golden mantella, for example, is bright yellow to orange, while the Betsileo golden frog is gold or orange gold with black sides. Scientists think the bright colors warn predators to leave the frogs alone. The poison in the mantellas is like that found in many of the poison frogs of South and Central America, but it is not as strong. It is, however, powerful enough to convince predators to pass by the frogs and look for something else to eat.

Some of the Asian treefrogs build foam nests. The gray treefrog is an example. First, a pair of frogs finds a spot in a tree branch that hangs over the water. Next, the female oozes a fluid before she lays her eggs, and she alone, or she and her mate, kick the fluid with their hind legs to whip it into foam. Once they have made a large amount of foam, she lays her eggs inside. The outside of the foam nest dries and hardens, but the inside stays moist. The eggs soon hatch into tadpoles inside the nest. By this time, the nest's bottom has become soft, often dissolving in a rain storm, and the tadpoles drop out of the bottom to the water below.

Except for the mantellas, mating in Asian treefrogs is mainly a nighttime activity. The males call to keep other males away and to attract females. The male common treefrog has a call that sounds like a deep quack; the male golden mantella makes quick, clicking noises; and males of other species have their own calls. In most species, the males call from or near a hidden spot or from a place where predators cannot easily reach. The male Buerger's frog calls from rocks in fast-moving streams, for instance, and the male Eiffinger's Asian treefrog does his calling next to the tree hole where he will mate. The mantellas, however, are very bold. These brightly colored males call loudly from open places in plain sight. Their colors serve them well at this time of year. They not only continue to warn predators of their poisonous skin and usually keep the frog safe, but they also tell other male frogs that an area is already taken. Sometimes two males fight over a good calling site. One will grab the other around the head and upper legs and try to push it away. This same type of fighting sometimes happens with female mantellas, but it is less common.

During mating, males typically climb onto the female's back and slowly squirt a fluid, which contains microscopic cells called sperm, onto the eggs while the female lays them. In the foam-nesting species, the male adds his fluid to the foam. In the gray treefrog, more than one male may add fluid. The eggs all have the same mother, but the father is whichever male added the sperm to the egg. In this way, the eggs in one nest may have several fathers.

In those species of Asian treefrogs that do not make foam nests, only one male mates with each female, and her young all have the same father. Sometimes, however, one male may mate with more than one female, and therefore be the father to several clutches of eggs. Depending on the species, the frogs may lay their eggs in foam nests, as described above, in tree holes, on the ground, or in still water. The painted Indonesian treefrog is one of the species that uses tree holes. A male and a female mate inside the tree hole over a puddle of water inside. The eggs stick to the inside wall of the tree. When they hatch, the tadpoles fall out of the eggs and into the water below. The Luzon bubble-nest frog is one of many species in which the female lays her eggs on the ground. In these species, the female usually lays only one dozen to three dozen eggs at a time. The Luzon bubble-nest frog, for instance, lays between five and nineteen large eggs. Like many other ground layers, she actually lays her eggs on the base of a leaf. Her eggs develop right into froglets there on the leaf, never becoming tadpoles in between.

Although the male golden mantellas usually do their calling from spots where they can be seen, male and female pairs mate in secret. Once a female approaches a calling male, the two find a hiding spot under a piece of bark or a rock that is next to some water. The eggs hatch into tadpoles, which then wriggle over the ground a short way until they plop into the water. The arboreal mantella, which is also sometimes known as the Folohy golden frog, mates differently. In this species, the female lays only one egg, which she sticks on an object above a puddle of water. Often, this puddle is inside a broken, standing piece of bamboo. The arboreal mantella is one of the only frogs in the world that lays one egg at a time.

Other frogs in this family breed in water. These include Buerger's frog and the forest bright-eyed frog, which both mate and lay their eggs in streams. The eggs hatch into tadpoles that continue growing in the water and eventually change into froglets.

Most of the frogs in this family breed over many weeks each year, but a few species mate during a very short period of only a few days. After they mate and lay their eggs, the males and females of many species leave their young to develop on their own. In a few species that do not lay their eggs in the water or in foam nests, the males will sit atop the clump of eggs while they develop. This may help to keep them moist or may help protect them from predators that might otherwise eat them. Some females of the foam-nesting species also stay nearby, sometimes returning to the nest to add more foam if necessary. They may even urinate on the nest to keep it moist enough for the eggs to survive.

The female Eiffinger's Asian treefrog lays her eggs on the inside of a tree hole and cares for her young. Instead of protecting them from predators or making sure they are moist, she feeds them. The water in the tree hole sometimes has little to feed the growing tadpoles, so she lays extra eggs in the water for her tadpoles to eat. Since these extra "blank" eggs have never mixed with sperm from a male, they would never have developed into young frogs, even if the tadpoles did not eat them. Arboreal mantellas do something similar. The female will drop a "blank" egg into the water for her tadpole to eat. Sometimes, however, the male becomes involved and leads another female to the water where one of his tadpoles is developing. If she lays her egg there, it may hatch into a tadpole that will become food for its older sibling.

The tadpoles of the common treefrog get no extra food from their parents. When they drop from their foam nests into the water, these hungry youngsters use their sharp and powerful beaks to eat almost anything in sight. If the water is just a small puddle, they may even eat their nest mates. Sometimes, only one tadpole is left in the puddle by the time it changes into a froglet.

JUST HOW MANY?

The number of species in the Asian treefrog family is uncertain. Some people separate out a group of the frogs into a separate family, called Mantellidae, but even when they are included, the overall number of species may differ by nearly one hundred. For example, the World Conservation Union (IUCN), which keeps track of risks facing different species, has a different total number than AmphibiaWeb, which is an online system offered through the University of California at Berkeley. The IUCN lists 156 species in the Mantellidae family and another 262 Asian treefrogs for a total of 418 species. AmphibiaWeb, on the other hand, counts 150 species in Mantellidae and 224 Asian treefrogs, which adds up to 374 species.

Depending on the species, tadpoles take different amounts of time before they change into froglets. The western white-lipped treefrog usually needs one or two months. Golden mantellas also take one-and-a-half to two months, but other mantella species may need a longer time to change into froglets.

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over 10 years ago

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