(Megophryidae)
Class: Amphibia
Order: Anura
Family: Megophryidae
Thumbnail description
Small to large frogs that are exceptionally well camouflaged and often secretive
Size
0.59–5.51 in (15–140 mm)
Number of genera, species
11 genera; 107 species
Habitat
Forest, mountain streams
Conservation status
Not threatened
Distribution
Eastern Asia
Evolution and systematics
Asian toadfrogs are a group of frogs with diverse morphologic features, and there is not one character that easily defines them. For this reason, using anatomy to form an understanding of the natural groupings within the megophryids or their relationship to other frog families has been difficult. There are no fossil megophryids, and thus the age of this group and its ancient distribution cannot be confirmed. Like other organisms with similar distributions and limitations to dispersal, their current ranges are the result of geologic events that took place more than 30 million years ago. In the Late Oligocene, the sea levels were much lower than they are today, creating a continuous landmass from mainland Asia to the Indo-Australian archipelago, including a portion of the Philippine islands. The tropical rainforest climate at that time was similar to the environments where megophryids are found today, and many of the megophryid genera likely were established and distributed across much of this area. Subsequent fluctuations in sea levels and shifting tectonic plates eroded these land-bridge connections, isolating representatives of Megophrys, Xenophrys, and Leptobrachium on many islands, including Borneo, Sumatra, Java, and the Philippines. The radiation of Scutiger and Oreolalax is intimately tied to the uplifting of the Tibet plateau that followed the collision of the Indian plate with Eurasia some 50 million years ago.
As of the year 2002, the family Megophryidae included 107 species divided among 11 genera and two subfamilies. The arrangement of tubercles on the hand and two distinct types of tadpoles easily distinguish the subfamilies. The subfamily Leptobrachiinae includes Leptobrachella, Leptobrachium, Leptolalax, Oreolalax, Scutiger, and Vibrissaphora. In this group a large tubercle is present at the base of the first finger. The tadpoles of all of these genera typically have a downward oriented mouth and a robust keratinized horny beak on both the upper and lower jaws. The subfamily Megophryinae includes Atympanophrys, Brachytarsophrys, Megophrys, Ophryophryne, and Xenophrys. The tubercle on the hand, at the base of the first finger, extends well onto the thumb. The tadpoles have a large umbelliform (funnel-like) mouth that is directed upward. The keratinized beak is reduced and present only on the margin of the lower jaw.
All Asian toadfrogs have eight vertebrae and intervertebral discs that are not fused to adjacent vertebrae at the time of metamorphosis. The sacral diapophyses are dilated, and the pectoral girdle is arciferal, with a long bony sternum. On the roof of the mouth the neopalatines are absent; to compensate, a palatal process of the maxilla is elongated. Asian toadfrogs share a common ancestor with North American and European spadefoot toads (Pelobatidae) and parsley frogs (Pelodytidae). Some researchers have recognized these three families as the suborder Pelobatoidea. Asian toadfrogs can be distinguished from their sister groups by their paddle-shaped tongue and a hyoid that is simplified and elongated; the hyoid lacks any remnant of a cartilaginous connection to the back of the skull.
Physical characteristics
Asian toadfrogs come in just about every size and shape imaginable. The largest species, the broad-headed toad (Brachytarsophrys), attains a maximum length of 6.6 in (168 mm), and the smallest species, the Borneo frog (Leptobrachella), is a mere 0.7 in (17.8 mm) long. Females are typically larger than males, except among the moustache toads (Vibrissaphora) and two species of alpine toads (Scutiger). Other sexually dimorphic characters include keratinized nuptial patches on the chest and fingers of breeding male alpine toads and cateyed frogs (Oreolalax) and bizarre keratinized spines seen on the upper lip of the male moustache toad during the breeding season.
The group takes its family name from the genus Megophrys, derived from Greek words (meg + ophrys) that mean "large eyebrow." This refers to the species Megophrys montana, which has long, fleshy appendages above the eyes. This trait is present in most species of Megophryinae, though it is not as pronounced. Leptobrachiinae includes two genera of warty toadlike species, the cateyed frogs and alpine toads. The remainder of the Leptobrachiinae, the slender frogs (Leptolalax), leaf litter frogs (Leptobrachium), and moustache toads, are not as toadlike, but they have fairly large eyes in proportion to their heads. The Borneo frog has unique toe disks that are swollen and have a pointed tip; all other megophryids have simple rounded toes with no visible disks. The pupils are vertical in all genera except the Borneo frog and the mountain toad (Ophryophryne), in which they are either horizontal or diamond-shaped. The color pattern is generally cryptic, but in some species the males may exhibit breeding coloration in the form of bright highlights on the digits or vocal sac, and even fewer have brilliant spots (red, yellow, or orange) along the flanks or thighs.
Distribution
Asian toadfrogs occur throughout Southeast Asia, as far north as Shanxi, China; south to the island of Java (Indonesia); and east from Bengal, India, to Mindanao in the Philippines. The Asian horned frog (Megophrys montana) has been collected at sea level on the beaches of Sarawak, whereas the Nyingchi lazy toad (Scutiger nyingchiensis) has adapted to the harsh climate at 16,732 ft (5,100 m) on the southern slopes of the Himalayas. Of the 11 genera of megophryids, only one genus, Leptobrachella, occurs exclusively on the island of Borneo (Indonesia and Malaysia) or a nearby oceanic island. The most widely distributed genus and the largest, in terms of number of species, is Xenophrys. It occurs throughout much of the range of the family at moderate elevations, between 1,968 and 6,889 ft (600–2,100 m). Leptobrachium and Leptolalax have a more restricted distribution that covers southern China, Indochina, and the island of Borneo; Ophryophryne and Brachytarsophrys occur in Vietnam and southern China. The five species of Vibrissaphora live on only two widely disjunct mountain ranges in southern China and northern Vietnam. Because of their preference for montane habitats, certain species in each genus are unique to a specific mountain range. Of the 107 species of Asian toadfrogs, 26 are known from only a single location.
Habitat
Asian toadfrogs have an extensive north-south distribution that encompasses temperate to tropical rainforest climates. In their northern distribution (approximately 8–35° north latitude), they are found in seasonal monsoon forests where the dry season may last 2–5 months and where the annual rainfall is 106 in (270 cm) a year. In their southern equatorial limit, they occur in aseasonal tropical rainforests in which the annual rainfall may be as much as 263 in (668 cm) a year. Asian toadfrogs require primary or old-growth secondary montane forests. In either case, the forest canopy is generally dense, and the ground is covered with accumulated leaf litter. The tadpoles need clear mountain streams of varying depths. The slender-bodied tadpoles of Leptolalax and Leptobrachella live in swift torrents among the small stones that line the streambed. Larger-bodied tadpoles, such as those of Leptobrachium, Vibrissaphora, Scutiger, and Oreolalax occupy the deeper splash pools, where they are able to avoid the current. The funnel-mouth tadpoles opt for calmer edges of larger streams or are found in the clear, shallow seeps that are scarcely deeper than the tadpoles' bodies.
Behavior
Asian toadfrogs are nocturnal, coming out at dusk to forage and breed. In seasonal climates, their activity is dictated by the wet and dry seasons, but in the tropics they may be active all year long. In the north, breeding takes place during the wet season; Asian toadfrogs may be very abundant at this time. During the dry season it is difficult to find Asian toad-frogs, and it is thought that they return to the forest, taking refuge under rocks and logs. There is one report of five male moustache toads "hibernating" in a tree hole. Asian toadfrogs are poor jumpers; in fact, the leaf litter frog is more inclined to walk slowly away from a disturbance than it is to hop. The cryptic appearance of most species is their only defense against predation, but if they are threatened, the broad-headed toads will open their large mouths and lunge as if to bite.
Feeding ecology and diet
The broad-headed toads are sit-and-wait predators, consuming fairly large prey that may be moving along the forest floor. Little else is known about the foraging activities of the remaining species. Random examination of stomach contents has found that moths, spiders, crickets, cockroaches, beetles, scorpions, centipedes, and snails are all potential prey of Asian toadfrogs.
Funnel-mouth tadpoles feed on minute particles on the surface of the water. While feeding, the larvae position their upturned lips at the level of the water. Taking advantage of the gentle currents that they prefer, they simply allow water and any small particles on the surface film to flow over the edge of the funnel and into the mouth. Papillae (small fleshy fingerlike projections) around the lips direct the food particles into the mouth. When the papillae come in contact with a particle that is too large, the tadpole quickly dives to avoid the obstruction and resurfaces to resume the feeding process. The non–funnel-mouth tadpoles of Leptobrachiinae all forage on the detritus or algae that accumulate in streams. One study has shown that in the same microhabitat, leptobrachine larvae consume food particles that are on average three times the size of what the funnel-mouth tadpoles eat.
Reproductive biology
In seasonal climates breeding activity occurs during the wet season. In Vietnam, this is typically late fall to early spring, and it may last one to two months. In these climates, it is not uncommon to find peak breeding activity when evening temperatures are 41–44°F (5–7°C). Males also may be heard calling during the day, but these efforts are never made with the enthusiasm that is heard at night. Female leaf-litter frogs from Borneo are full of eggs in January, June, July, and August; these equatorial megophryids may breed all year round.
The males of most species situate themselves along the stream bank, either in the vegetation or under the boulders that are at the sides of the stream. The semi-arboreal Ophryophryne calls from vegetation up to 3 ft (1 m) above the ground. Larger species (Megophrys and Brachytarsophrys) space themselves 162–324 ft (50–100 m) along the stream bank. Smaller species, such as Leptolalax, Ophryophryne, and Scutiger, may form aggregations of five to 10 males along a 75-ft (23 m) stretch of a stream. The calls of Xenophrys, Brachytarsophrys, and Leptobrachium
sound like a guttural bark, "grrrack," whereas Ophryophryne produces a series of eight to 10 quick whistles. Leptolalax and Leptobrachella have calls made up of series of quick pulses that sound like a finger dragging across a comb. Amplexus is either axillary, where males clasp the females at the level of the shoulder, or inguinal, where males clasp females around the waist. Alpine toads (Scutiger) engage in inguinal amplexus and are said to use their keratinized chest patches to stimulate the female to lay eggs. The eggs always are deposited on the underside of large boulders at the edges of streams. Parental care has been recorded in the moustache toad—males remain with the clutches until they develop into tadpoles.
Conservation status
Asian toadfrogs vary from being extremely common to exceedingly rare. The slender mud frog (Leptolalax pelodytoides) has a vast distribution and during the breeding season can be the most abundant species in a stream habitat. On the other hand, Sung's slender frog (Leptolalax sungi) is known only from a 50-yd (50 m) stretch of one mountain stream. Efforts are being made to protect the rapidly disappearing habitat in which Asian toadfrogs live. As of the year 2002, no Asian toad-frogs were listed as endangered or threatened by the IUCN.
Significance to humans
During the winter breeding season, when Asian toadfrogs are most abundant, the larger species, such as the Annam broad-headed toad (Brachytarsophrys intermedia), are eaten by local people. The immediate relevance of the smaller species to humans has not been discovered. Given their preference for mature, undisturbed forests and the larval requirement for clean streams, however, they may prove to be a valuable indicator for evaluating the health of Southeast Asian montane forests.
Species accounts
Bana leaf litter frogSlender mud frog
Schmidt's lazy toad
Ailao moustache toad
Annam broad-headed toad
Asian horned frog
Asian mountain toad
Burmese spadefoot toad
Resources
Books:Bourret, René. Les Batraciens de l'Indochine. Vol. 6. Hanoi: Institut Océanographique de l'Indochine, 1942.
Duellman, William. E., and Linda Trueb. Biology of Amphibians. New York: McGraw-Hill Book Co., 1986.
Inger, Robert, F. "Distribution of Amphibians in Southern Asia and Adjacent Islands." In Patterns of Distribution of Amphibians: A Global Perspective, edited by William Duellman. Baltimore: Johns Hopkins University Press, 1999.
Zhao, Er-Mi. "Distribution Patterns of Amphibians in Temperate Eastern Asia." In Patterns of Distribution of Amphibians: A Global Perspective, edited by William Duellman. Baltimore: Johns Hopkins University Press, 1999.
Zug, George R., Laurie J. Vitt, and Janalee P. Caldwell. Herpetology: An Introductory Biology of Amphibians and Reptiles. 2nd ed. San Diego: Academic Press, 2001.
Periodicals:Dring, Julian. "Frogs of the Genus Leptobrachella (Pelobatidae)." Amphibia-Reptilia 4, no. 2–4 (1983): 89–102.
Dubois, Alain, and Annemarie Ohler. "A New Species of Leptobrachium (Vibrissaphora) from Northern Vietnam, with a Review of the Taxonomy of the Genus Leptobrachium (Pelobatidae, Megophryinae)." Dumerilia 4, no. 1 (1998): 1–32.
Inger, Robert F. "Diets of Tadpoles Living in a Bornean Rain Forest." Alytes 5, no. 4 (1986): 153–164.
Lathrop, Amy. "Taxonomic Review of the Megophryid Frogs (Anura: Pelobatoidea)." Asiatic Herpetological Research 7 (1997): 68–79.
Xie, Feng, and Zhuwang Wang. "Review of the Systematics of Pelobatids (Anura: Pelobatidae)." Cultum Herpetologica Sinica 8 (June 2000): 356–370.
Other:Frost, Darrel R. Amphibian Species of the World: An Online Reference. Vers. 2.20. 1 Sept. 2000 (8 May 2002) .
Orlov, Nikolai, Roman Khalikov, Robert W. Murphy, and Amy Lathrop. Atlas of Megophryids (Megophryidae: Anura: Amphibia) of Vietnam. Compact Disc. Saint Petersburg: Zoological Institute of Saint Petersburg, 2000.
[Article by: Amy Lathrop, MA]
