Ruthven's Frog: Allophrynidae

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RUTHVEN'S FROG: Allophrynidae

PHYSICAL CHARACTERISTICS

Ruthven's frog is a metallic brown color, sometimes yellow- or gray-brown, with darker marks and lighter yellow-brown or gold stripes down each side of the back. The back of its long body is scattered with tiny spikes, or spicules (SPIK-yuhlz), that are partly buried in the skin. The spicules in males are larger than those in females. Because of the spicules, which look somewhat like warts, people often describe this frog as toadlike. It has large eyes that bulge from each side of its head. The head becomes flatter toward the front. Its front and back legs are thin, and the toes end in rounded pads. The front legs often have noticeable light-colored spots that extend onto the chest and throat. Light-colored spots also cover the lower part of its head around the mouth. Often, the sides of the body and parts of the legs have a pink, see-through appearance.

Males have a dark, unspotted area on the throat that remains hidden except when they call. During calling, this area, called a vocal sac, blows up to a large size—at least the size of the head and sometimes much larger. The females grow slightly larger than the males. Females typically reach 0.85 to 1.20 inches (2.2 to 3.1 centimeters) long from snout to rump, and males usually grow to 0.8 to 1 inch (2.1 to 2.5 centimeters) in length.

Discovered in 1926, the single species of Ruthven's frog has at one time or another been listed in five different frog families, including the true toads, the glass frogs, the leptodactylid frogs, the tree frogs, and its own separate family, as it is listed here. Scientists have found no fossils to study. The confusion in the listing of this frog's family comes from the fact that the frog has some features of all of the different families. For example, its toe bones are T-shaped at the tips, which scientists once thought was like the toes of the glass frogs or possibly the tree frogs. Studies since then showed that the toe bones of Ruthven's frogs are actually slightly different than those of either the glass or the tree frogs.

During the mating season, male Ruthven's frogs call from plants and trees above ponds, and females lay their eggs in the water, which is the same situation as seen in the tree frogs. Like true toads, Ruthven's frogs have no teeth. In fact, the scientific name of Ruthven's frogs, Allophryne, means "other toad," because it was thought to be a new kind of true toad.

Ruthven's frog's full scientific name is Allophryne ruthveni. Like many other species of plants and animals, the second part of its name refers to a person or to the place where it was collected. In this case, the name refers to Alexander Ruthven, a noted herpetologist (her-peh-TOL-eh-jist) who was very active in the first half of the twentieth century. A herpetologist is a person who studies amphibians and reptiles. Ruthven, who was curator of the Division of Reptiles and Amphibians at the University of Michigan Museum of Zoology, led eighteen of the museum's expeditions to places throughout the United States, Mexico, Central America, and South America.

HERPETOLOGIST EXPLORERS

Helen Thompson Gaige, who in 1926 was the first person scientifically to describe Ruthven's frog, was one of the earliest, well-known, female herpetologists. Gaige, who lived from 1886 to 1976, named many new species of frogs, especially those from Central and South America. Ruthven's frog is a South American species. Her career included positions as scientific assistant and then curator of the Division of Reptiles and Amphibians at the University of Michigan Museum of Zoology (UMMZ). Ruthven's frog carries the name of Alexander Ruthven, another respected herpetologist from the early twentieth century. He traveled through much of the New World studying amphibians and reptiles. Ruthven was curator of the UMMZ Division of Reptiles and Amphibians from 1906 to 1936, the museum director from 1913 to 1929, and president of the University of Michigan from 1929 to 1951.

In 2002, a group of scientists compared the DNA of Ruthven's frogs to the DNA of other frogs. DNA is a string of chemicals that provides the instructions for making a living thing. By comparing the DNA of different organisms, scientists can tell how similar they are. The comparison showed that Ruthven's frogs may be most closely related to the glass frogs and perhaps should be considered members of that family. Until more studies are done, however, many scientists list Ruthven's frogs as the lone members of its own family, called Allophrynidae, while some others still place it in the family Hylidae. In 2003, scientists discovered what they believe may be a second species of Ruthven's frog. It is black with bright white and yellow spots and has two bulging eyes, one on each side of its head.

GEOGRAPHIC RANGE

Ruthven's frog was first found in Tukeit Hill below Kaiteur Falls in Guyana in northern South America. It has since been seen in many parts of South America, including north-central Brazil, French Guiana, Guyana, Suriname, and Venezuela. Since scientists have not yet fully explored the area around the Amazon River where this frog lives, other populations of Ruthven's frogs probably remain undiscovered. In addition, a possible second species of Ruthven's frog has been discovered in Peru.

HABITAT

Ruthven's frogs live in lowland forests rather than forests on hillsides or in the mountains. This frog usually goes no higher on hillsides than about 656 feet (200 meters) above sea level and stays in forests that have not been logged but, nevertheless, are not too thick with plants and trees. Throughout the year, they typically stay in areas near rivers and streams. During the rainy season, they group together around low spots in the forest that fill with rain or overflowing river water.

DIET

Scientists have not studied this small frog in enough detail to learn what it eats. If it follows the pattern of the glass frogs and many other types of frogs, however, it eats small insects.

BEHAVIOR AND REPRODUCTION

They are nocturnal (nahk-TER-nuhl), which means that they are active at night. During this time, they move around the forests near rivers and streams. They climb through trees and large bushes and onto the leaves of branches that may be several feet (1 to 3 meters) above the forest floor. Sometimes they sit in bromeliads (BRO-mee-lee-adds), which are plants that grow in warm, usually tropical forests often on other plants. Many bromeliads have leaves that overlap into cup shapes that can hold water and are very attractive spots for frogs and insects.

One of the frog's predators is a snake known by its scientific name of Leimadophis reginae. Scientists learned about the snake's appetite for the frogs when they captured one of the snakes on the edge of a river in Suriname, which is in northern South America. They cut open the snake's stomach and found a pregnant female Ruthven's frog inside.

The rainy season in the part of South America where the Ruthven's frog lives lasts from about January to July, although it is shorter in some places. The rains create small pools of water in dips in the forest floor and also cause rivers and streams to overflow onto banks and into other small pools of water. As long as the rains continue, the pools stay wet, but when the rainy season ends, they start to dry up. Since the pools only remain wet for part of the year, they are called temporary pools. The frogs make use of these temporary pools. The males hop to the edges of the water, or sometimes onto the leaves of low-hanging tree and bush branches, and begin calling. The call is a string of short low notes that together sound like a trill. Researchers studied the call by making a recording as a male trilled. They were able to count eighteen notes per second in its trill. Many males may call from the same place. This kind of group singing is known as a chorus (KOR-us).

Scientists found an especially large chorus in a pond near Pará, which is in northern Brazil. The pond actually formed when rains flooded the Amazon River and its tributaries, which are the smaller rivers and streams that flow into the Amazon. One of the tributaries, the Rio Xingu, overflowed to make the pond. Only a few frogs called from the pond for two months, but on one night in March, several hundred frogs suddenly showed up. Apparently, the frogs waited to mate until the tributary had flooded enough to fill the pond with a great deal of water. This type of mating, which happens during a short period of time and includes a large number of frogs, is called explosive breeding.

To mate, the male grasps the female from behind and near her front legs. While the male is in this piggyback position, called amplexus (am-PLEK-sus), the female lays her eggs, which number in the hundreds, in the water. Scientists learned how many eggs they lay by capturing a pair of mating frogs, dropping them in a plastic bag, and then counting as the female laid three hundred eggs. None of the eggs lived to hatch, however, and scientists still do not know what the Ruthven's frog tadpoles look like.

RUTHVEN'S FROGS AND PEOPLE

People rarely see this frog in the wild, although it is actually quite common in the parts of South America where it lives. Scientists find it interesting because they do not know exactly where it fits in the family tree of all frog species. Once they find tadpoles or possibly a fossil of a frog, however, they may learn details that will help them decide if the Ruthven's frog should stay in its own family or should be included in another family, such as the glass frogs.

CONSERVATION STATUS

The World Conservation Union (IUCN) does not consider Ruthven's frog to be at risk. It lives in an area that is seldom visited by humans, and the frog is quite common there. The frog has not been studied well, however, and scientists are unsure where all of the populations are located. Some populations that have not yet been discovered may live in parts of the South American forest that are currently being logged.

FOR MORE INFORMATION

Books:

Caldwell, Janalee P. "Diversity of Amazonian Anurans: The Role of Systematics and Phylogeny in Identifying Macroecological and Evolutionary Patterns." In Neotropical Biodiversity and Conservation, edited by A. C. Gibson. Los Angeles: Mildred E. Mathias Botanical Garden Miscellaneous Publications, 1996.

Showler, Dave. Frogs and Toads: A Golden Guide. New York: St. Martin's Press, 2004.

Zug, George. Herpetology: An Introductory Biology of Amphibians and Reptiles. San Diego, CA: Academic Press, 1993.