True frogs

(Ranidae)

Class Amphibia

Order Anura

Family Ranidae

Thumbnail description
Small to large firmisternal aquatic or terrestrial frogs with a toothed upper jaw and cylindrical sacral diapophyses, without intercalary elements between penultimate and terminal phalanges of the digits

Size
0.4–12.6 in (10–320 mm)

Number of genera, species
51 genera; 686 species

Habitat
Ranids live in a variety of habitats, including tropical, subtropical, and temperate forests; savannas; grasslands; deserts; and high-elevation sites

Conservation status
Extinct: 3 species; Critically Endangered: 7 species; Endangered: 6 species; Vulnerable: 14 species; Lower Risk/Near Threatened: 4 species; Data Deficient: 12 species

Distribution
Ranids occur throughout the Old World (Eurasia, Africa), on most western Pacific islands, and in northern Australia, North America, and the northern part of South America; absent in the Pacific east of Fiji, in Madagascar (except as introduced), and on numerous isolated oceanic islands

Evolution and systematics

Ranid fossils are known reliably only since the Eocene of Europe, but the fossil record is of little help for the reconstruction of the early history of the group. Although it seems clear that the group is Gondwanan, current evidence does not allow unambiguous distinction between an Asian or an African origin. Molecular data from mitochondrial genes and a few nuclear genes suggest the existence of a monophyletic group (called by some researchers the "epifamily Ranoidae" of the "superfamily Ranoidea") made up of two monophyletic subgroups generally treated as families (Mantellidae and Rhacophoridae) and a third subgroup, the Ranidae, the monophyly of which is highly questionable. The latter subgroup contains several groups that are treated herein as subfamilies or tribes.

Five of these groups (Cacosterninae, Conrauini, Petropedetinae, Ptychadeninae, Pyxicephalinae) seem to be endemic to tropical and southern Africa, and nine (Ceratobatrachini, Limnonectini, Paini, Lankanectinae, Micrixalinae, Nyctibatrachinae, Occidozyginae, Amolopini, Ranixalinae) are endemic to the Oriental region. A fifteenth group (Dicroglossini) is distributed in both regions, and a sixteenth (Ranini) is present in those two regions as well as the Holarctic and the northern parts of South America and Australia.

Most ranids have 13 pairs of chromosomes, but various species have different numbers of chromosomes. Besides the generalized development in water through a tadpole stage, various kinds of direct development (endotrophy) have evolved independently in several clades. Much variation exists in the labial tooth-row formula besides the generalized and probably plesiomorphic formula of 2/3; a few groups, especially those with rheophilic tadpoles, have up to 14 rows on the anterior lip and 12 on the posterior lip; in a few genera, labial teeth are absent on one or both lips.

The phylogenetic data currently available support the provisional recognition of eleven subfamilies, within some of which distinct tribes can be recognized.

Cacosterninae

This subfamily includes six to eight genera in sub-Saharan Africa: Anhydrophryne (one species), Arthroleptella (three species), Cacosternum (seven species), Microbatrachella (one species), Nothophryne (one species), Poyntonia (one species), and possibly also Strongylopus (six species), and Tomopterna (eight species). These are minute to medium-size frogs, including some of the smallest known anurans (0.4 in, or 10 mm, in Microbatrachella). Most of these genera have a partially or entirely cartilaginous omosternal style and procoracoid clavicular bar; the latter is sometimes incomplete. Known chromosome numbers are 26 (Anhydrophryne, diploid Tomopterna), 24 (Poyntonia), and 52 (tetraploid Tomopterna). Development is exotrophic in most genera; tadpoles have 1–4/2–3 rows of labial teeth. Anhydrophryne and Arthroleptella lay five to 40 eggs, 0.09–0.2 in (2.2–4.5 mm) in diameter, under shelters, where they undergo direct development.

Dicroglossinae

Despite anatomical heterogeneity, monophyly of this group is established firmly by molecular data. Many members share several characters, including a peculiar scapular girdle with slightly overlapping coracoids, the lowest one having a slight concavity medially; a basally forked omosternum; large nasals in contact medially; no dorsolateral folds; and small numbers of large eggs. Five subgroups are treated provisionally as tribes:

• Ceratobatrachini: This tribe includes five genera on western Pacific islands and in southern Indochina. These genera are Ceratobatrachus (one species), Discodeles (five species), Ingerana (five species), Palmatorappia (one species), and Platymantis (about 50 species). There are 20–26 known chromosome numbers in the latter genus. Most species in this tribe have dilated digital tips, commonly with a dorsoterminal groove. Females lay four to 47 eggs, 0.09–0.2 in (2.2–5.0 mm) in diameter, under objects or in burrows, where they undergo direct development.
• Conrauini: The unique genus Conraua (six species), from tropical sub-Saharan Africa, includes Conraua goliath, the largest living anuran (reaching 12.6 in, or 320 mm, in snout-vent length). This genus is characterized by an exceptional development of the procoracoid cartilage and by the medial divergence of the coracoids and clavicles. The diploid chromosome number of Conraua crassipes is 26. Males of this genus lack vocal sacs, but they have a unique mode of calling, a strident whistling emitted with an open mouth. Rheophilic tadpoles have 7–14/6–12 labial tooth rows. The current assignment of this tribe to the Dicroglossinae is only tentative.
• Dicroglossini: This group is composed of six genera distributed in southern Asia (India and neighboring countries). Three genera (Minervarya, one species; Nannophrys, three species; Sphaerotheca, three species) are restricted to this region. The distributions of the other three genera include other regions: Fejervarya (about 20 species) also occurs in most of the Oriental region, Euphlyctis (three species) occurs in the Near East and the Arabian peninsula, and Hoplobatrachus (six species) is found in China, Indochina, and tropical Africa. The chromosome numbers are 26 and 52 (tetraploid Hoplobatrachus). Hoplobatrachus is one of the few well-supported genus-group taxa for which there is substantial of a distribution that includes tropical Asia and tropical Africa but not the Near East. Besides molecular and morphologic data, the monophyly of this genus is supported by its unique tadpole, which has strong jaw sheaths and double tooth rows, a unique character in the Ranoidea. All species of this tribe are exotrophic, tadpoles have 1–5/2–6 rows of labial teeth. Tadpoles of the strange, crevice-dwelling genus Nannophrys are semiterrestrial, with elongated bodies and low tail fins, a condition that is strikingly convergent with that of the genus Indirana, a member of a distinct ranid lineage. Adults of the aquatic Euphlyctis genus retain the larval lateral-line system.
• Limnonectini: This tribe encompasses two genera from Indochina, southern China, and the western Pacific islands: Limnonectes (about 50 species) and Taylorana (six species). Known chromosome numbers are 22–26. Many species have dilated digital tips with a dorsoterminal groove and various combinations of unusual male secondary sex characters, including the absence of nuptial pads and vocal sacs or an advertisement call, fanglike odontoids on the lower jaw, an enlarged head, and a knob on the posterodorsal part of the head. Most Limnonectes have free-swimming tadpoles with 1–3/1–3 rows of labial teeth; some species exhibit parental care, and some might undergo endotrophic development in the female genital tract. Males of the genus Taylorana dig nests in the mud, where they call; females deposit five to 13 large eggs (0.12 in, or 3 mm, in diameter) that undergo direct development.
• Paini: This group includes two genera in south-central Asia (through the Himalayas from Afghanistan to eastern China): Chaparana (six species) and Paa (about 30 species). Despite the fact that the omosternum is not forked at the base and the coracoids do not overlap but are connected by epicoracoid cartilage, several other morphologic characters as well as molecular data suggest that these frogs are members of the Dicroglossinae. Known chromosome numbers in Paa are 26 and 64; the latter most likely is a polyploid. Most species in this tribe have various combinations of unusual male secondary sex characters, including keratinized spines on the first three fingers, chest, belly, and forearms; hypertrophied forearms (Paa); or differentiated skin, sometimes bearing spines, around the vent (some Chaparana). These characters presumably facilitate breeding in fast-flowing waters up to elevations of more than 13,123 ft (4,000 m) in the Himalayas. Tadpoles have three to nine rows of labial teeth on the anterior lip but only three rows on the posterior lip.

Lankanectinae

The aquatic Lankanectes corrugatus from Sri Lanka has an unusual combination of characters, such as a forked omosternum; skin folds on the head, body and limbs; retention of the lateral-line system in adults; and vocal sacs and fanglike odontoids on the lower jaw of males but absence of nuptial pads. The tadpole has 2/3 rows of labial teeth.

Micrixalinae

The genus Micrixalus (about 10 species) is endemic to the Western Ghats in southern India. These small frogs have nonoverlapping coracoids, an unforked omosternum, T-shaped terminal phalanges, no vomerine teeth or femoral glands, a tongue that usually has a median process, dorsolateral folds, smooth ventral skin, and tadpoles with 1/0 rows of labial teeth.

Nyctibatrachinae

The genus Nyctibatrachus (about 12 species) is found in the Western Ghats of India. These are the only known ranids with a vertical pupil. Other notable characters are the presence of femoral glands, T-shaped terminal phalanges, a forked omosternum, and, in tadpoles, jaw sheaths and numerous papillae on the labia but no labial teeth.

Occidozyginae

This subfamily includes Occidozyga (one species) and Phrynoglossus (10 species) in southeastern Asia and the western Pacific islands. This group is a well-characterized clade in most molecular phylogenetic analyses, some of which suggest that it could be the sister group to all other Ranoidae (including the Mantellidae and Rhacophoridae). The oral disc of the tadpole is reduced to a fleshy rim, without papillae, labial teeth, or an upper jaw sheath; the lower jaw sheath is horseshoe-shaped. The omosternum is forked basally, and vomerine teeth are absent. The chromosome number is 26. Adult Occidozyga retain the lateral-line system and have axillary amplexus. Adults of Phrynoglossus do not have lateral lines and engage in inguinal amplexus.

Petropedetinae

This group includes seven genera in sub-Saharan Africa: Arthroleptides (two species), Dimorphognathus (one species), Ericabatrachus (one species), Natalobatrachus (one species), Petropedetes (seven species), Phrynobatrachus (about 70 species), and Phrynodon (three species). This subfamily of frogs includes some of the smallest known anurans (0.4 in, or 10 mm, among some Phrynobatrachus). The terminal phalanges of the digits are T-shaped, and femoral glands may be present. Known chromosome numbers are 26 (Petropedetes), 24 (Dimorphognathus), and 16–20 (Phrynobatrachus). Development is exotrophic in most genera; tadpoles have 1–7/2–6 rows of labial teeth. Phrynodon sandersoni frogs lay 12–17 eggs, 0.09 in (2.3 mm) in diameter, on vegetation above ground, where they undergo direct development with the mother remaining in the vicinity.

Ptychadeninae

Three genera from sub-Saharan Africa, Hildebrandtia (three species), Lanzarana (one species), and Ptychadena (about 50 species), share several apomorphic characters, including the loss of the neopalatines; reduced clavicles that usually are fused with the anterior borders of the coracoids; a short, compact, bony metasternal style, fusing of the eighth presacral and sacral vertebrae, and reduction or absence of the otic plate of the squamosal. Frogs of the genus Ptychadena have 24 chromosomes. All species are exotrophic. Tadpoles of Hildebrandtia have 0/2 rows of labial teeth, and those of Ptychadena have 1–3/2 rows.

Pyxicephalinae

This group consists of two genera with widely different habitats and modes of life: Aubria (two species) is aquatic and lives in humid tropical forests in central Africa, whereas Pyxicephalus (three species), which is adapted to burrowing during dry seasons, occurs in savannas and semiarid to arid habitats in eastern and southern Africa. These two genera share several skeletal apomorphies, femoral glands, and tadpoles

swimming in compact schools, sometimes under the protection of adults that will attack potential predators. Pyxicephalus adspersus has 26 chromosomes. Tadpoles have 5/3 rows of labial teeth.

Raninae

This is the largest group of Ranidae. The coracoids do not overlap, the omosternum is not forked at the base, and the nasals usually are small and not in contact medially. These frogs typically have dorsolateral folds and deposit large numbers of small, pigmented eggs. The group includes two provisional tribes:

• Amolopini: This group contains several taxa that are treated by different authors as distinct genera, subgenera, or species groups. The two major ones are the Amolops group (about 40 species in four subgenera or genera: Amo, Amolops, Huia, and Meristogenys) and the Odorrana group (about 30 species in at least three subgenera or genera: Chalcorana, Eburana, and Odorrana). These frogs live in or along swift torrents in the Himalayas and mountains of southern and eastern China, in Indochina, and on the western Pacific islands. They have long hind limbs, smooth venters, and large digital discs with ventrolateral grooves. Tadpoles of the Odorrana group have generalized mouthparts and 4–5/3–5 rows of labial teeth. The gastromyzophorous tadpoles of the Amolops group are adapted even better to torrent life. They have 4–12/3–10 rows of labial teeth and a sucker on the anterior part of the belly; additionally, they usually have integumentary glands on the body and tail and keratinized spinules in the skin. The known chromosome numbers are 26 and 27 (sexually dimorphic in some Amolops).
• Ranini: This is an unresolved, partly catch-all tribe that includes Batrachylodes (eight species) on the Solomon Islands, Nanorana (three species) in Tibet and surrounding high mountains, Staurois (three species) in the western Pacific, and a heterogeneous, nearly cosmopolitan assemblage traditionally called Rana (about 200 species), among which more than 35 subgenera and species groups are recognized. These groups include all the well-known Palearctic Ranidae (subgenera Pelophylax and Rana sensu stricto) and American Ranidae (subgenera Amerana, Aquarana, Lithobates, Pantherana, and related groups). They also encompass a few African groups (subgenera Afrana and Amietia) and numerous Asiatic groups (subgenera Babina, Glandirana, Nasirana, Nidirana, Pseudoamolops, Pseudorana, Pterorana, Rugosa, and several other poorly known taxa) as well as a few groups present in both regions (Hylarana and related groups). Chromosome numbers are 24, 26, and 27 as well as 39 and 52 in the triploid or tetraploid European Pelophylax. There are 1–10/2–9 labial tooth rows. Several groups in this tribe have T-shaped terminal phalanges with enlarged digit tips or even fully differentiated discs, but they always have ventrolateral grooves. Many adult males of these species have dorsolateral folds or particular macroglands or other secondary sex characters, such as humeral glands in Hylarana and related groups; suprabrachial glands in Babina and Nidirana; dagger-like prepollex (both sexes) in Babina; and vocal sacs, nuptial pads, and advertisement calls. Some Babina and Nidirana that lay eggs in mud nests engage in simple parental care. In Batrachylodes, there is probably direct development of terrestrial eggs.

Ranixalinae

The genus Indirana (about 10 species) occurs in the Western Ghats in southern India. These frogs are characterized by their unusual Y-shaped terminal phalanges, digital discs, femoral glands, and semiterrestrial tadpoles with 3–5/3–4 rows of labial teeth, elongated bodies, and low tail fins, which can make long jumps on the ground to escape predators.

Physical characteristics

Few derived characters are common to all groups currently included in the Ranidae. These frogs usually have a firmisternal pectoral girdle, in which the coracoids do not overlap and are connected by an epicoracoid cartilage; however, some groups have a pseudofirmisternal pectoral girdle, in which the coracoids do overlap and are fused to each other. The omosternum usually is ossified and may be forked or unforked basally. The metasternum generally is ossified. There are eight procelous presacral vertebrae, and the last two presacrals are not fused. The sacral diapophyses are cylindrical or slightly dilated. The carpal bones are composed of six elements: the first and second carpals and the first centrale are free, and the third carpal is fused with the fourth and fifth carpals and with the second centrale. Intercalary elements are absent between the penultimate and terminal phalanges of the digits. The terminal phalanges may be simple, slightly dilated, and T-shaped or Y-shaped. All species have teeth along the upper jaw, and most of them have vomerine teeth or ridges. The musculus sartorius is distinct from the musculus semitendinosus, and the tendon of the latter passes dorsal to the musculus gracilis. The musculus cutaneus pectoris usually is present. Most other characters vary.

Most species have 26 chromosomes, but 16–27 are known in nonpolyploid taxa. Polyploidy is not uncommon; tetraploidy (52 chromosomes) has been reported in several groups (Hoplobatrachus, Pelophylax, and Tomopterna), and some members of Paa have up to 64 chromosomes. Triploidy (39 chromosomes) is common in European members of Pelophylax.

The snout-vent length varies from 0.4 in (10 mm) in several minute African frogs (Arthroleptella and Phrynobatrachus) to more than 12.2 in (310 mm) in the African Conraua and the large Discodeles in the Solomons and neighboring islands. Many aquatic or terrestrial species are 1.6–3.3 in (41–84 mm) in length and have elongated bodies and long limbs. Some stream-adapted forms (e.g., Amolops and Odorrana) have particularly long hind limbs, whereas a few burrowing taxa (Pyxicephalus, Tomopterna, Sphaerotheca, and Hildebrandtia) have short, toadlike bodies with short limbs, spadelike metatarsal tubercles, and, sometimes, strongly ossified skulls. On the other hand, a few high-altitude taxa (Nanorana) have partly uncalcified skeletons.

Most ranids have moderate to extensive webbing that extends proximally between the outer metatarsals, but primarily terrestrial or semiarboreal and endotrophic taxa (e.g., Platymantis) have reduced webbing, and their outer metatarsals are not separated from each other. Many semiarboreal species or ones that live along or in running water have dilated digital tips or even differentiated terminal discs with grooves. Several kinds of digital discs, which are probably not homologous, exist in the Ranidae: dicroglossines have dorsoterminal grooves, and ranines have ventrolateral grooves. The latter condition includes a completely closed ventral "cell" bordered by a groove below the extremity of the digit; this feature occurs in some genera or subgenera of Raninae (Amo and Staurois) as well as in the Rhacophoridae and other arboreal families.

Different kinds of glandular structures may be present in the skin (e.g., various warts and folds on the dorsum and flanks, supratympanic folds, dorsolateral folds on the dorsum, rictal glands at the mouth commissure, humeral glands on the upper arm and suprabrachial glands above the arm insertion in males, and femoral glands on the posterior surfaces of the thighs in males or in both sexes). Taxa that climb on rocks (e.g., Ingerana and Staurois) have a granular venter similar to that in other arboreal families (Hylidae, Hyperoliidae, and Rhacophoridae). Various keratinized structures also arise on the skin, at least seasonally (e.g., nuptial pads bearing a layer of minute spinules on the thumb, or on the first two or three fingers, and on the prepollex, which is dagger-like in both sexes in Babina; larger spines in the same places and on the arms, chest, and belly in some stream-breeding species; and spines around the vent).

Males of many species are smaller than the females and have longer hind limbs and more extensive webbing; they also have enlarged forelimbs and internal or external (i.e., protruding through slits during calling) vocal sacs. In a few groups, males display special secondary sex characters, such as fanglike odontoids at the extremity of the lower jaw (e.g., Lankanectes, Limnonectes, and Taylorana), enlarged heads (Limnonectes), and knobs on the posterodorsal part of head (Elachyglossa).

Coloration varies widely, though rarely (e.g., some Amolops, Odorrana, and Pulchrana) is it as extraordinarily bright as in some other families, such as the Mantellidae or Dendrobatidae. Frogs living or breeding in lentic aquatic habitats tend to be a shade of green, whereas most terrestrial species that live primarily on the forest floor, especially in temperate regions with deciduous trees, commonly are shades of brown, like the color of dead leaves. Species living in savannas and grasslands usually have longitudinal marks or spots on the dorsum, whereas some aquatic species (Euphlyctis or Occidozyga) have black and white bars at the posterior surfaces of the thighs. Frogs that spend a large part of their lives on rocks in streams (e.g., Amolops, Ingerana, Odorrana, and Petropedetes) usually have variegated coloration. The iris coloration varies; generally there is a horizontal dark line continuous with a dark line on the canthus rostralis and another such line on or below the supratympanic fold. This contributes to camouflage of the eye, a particularly visible feature for many vertebrate predators. A dark vertical line also may be present, especially in the lower part of eye. The pupil typically is horizontally oval, but it may be rhomboidal or even vertical in a few species (Nyctibatrachus).

Some aquatic ranids (Euphlyctis, Lankanectes, and Occidozyga) show pedomorphic retention of the larval lateral-line system in adults. Tadpoles of ranids have a sinistral spiracle. Most have a generalized anteroventral, ventral, or almost terminal oral apparatus, with complete keratinized structures (upper and lower jaw sheaths and labial teeth) and marginal and submarginal oral papillae. Tadpoles of a few groups lack some of these structures. Occidozyginae lack papillae, tooth rows and the upper jaw sheath; the lower jaw is recessed and semilunar in shape. Nyctibatrachinae lack tooth rows on both lips; Micrixalinae lack them on the lower lip and Hildebrandtia on the upper lip. All other groups have rows on both lips. The common number of tooth rows is two on the upper lip and three on the lower lip, but many variations exist. Tooth rows are usually simple, except in the genus Hoplobatrachus, in which they are double.

Some groups have very specialized tadpoles. Tadpoles with very elongated bodies and tails with shallow tail fins (Indirana and Nannophrys) are semiterrestrial and may use the tail or, at later stages, the hind limbs to move over long distances on the ground. Numerous tadpoles that live in streams (Chaparana, Clinotarsus, Conraua, Nasirana, Odorrana group, Paa, Petropedetes, and Pseudorana) have muscular tails with low fins and a large oral disc with numerous papillae and many tooth rows, up to 14 on the anterior lip and 12 on the posterior lip. Some tadpoles (Amolops group and Pseudoamolops) have a large sucker that includes the oral disc and extends onto the anterior part of the belly. Tadpoles of some members of the Amolops and Hylarana groups have dermal glands on the body and sometimes on the tail. Certain ranid tadpoles have a dark tail tip (e.g., Fejervarya) or a large, brightly colored ocellus at the lateral base of the tail (Nasirana) that may attract predators, thus diverting attack from the head.

Distribution

The family is distributed throughout the Holarctic, except at higher latitudes and elevations, all of Africa except most of the Sahara, the Oriental region and western Pacific islands to Fiji, northern Australia, Central America, and the northern part of South America. It is absent (except as introduced) from Madagascar, New Zealand, New Caledonia and the Pacific islands east of Fiji, most of Australia and South America, the West Indies, many oceanic islands, and the Arctic and Antarctic. Because of the human consumption of frog legs, ranids were introduced by humans into Madagascar (Hoplobatrachus) and a number of continental regions and oceanic islands (mostly subgenera Aquarana and Pelophylax).

Habitat

The popular image of Rana as a green frog bathing in the sun on a water lily leaf is misleading. Although most European and North American ranids live close to ponds or lakes or move to these lentic habitats for breeding, this does not apply to the whole family. Many tropical ranids live or breed in slowly flowing or swiftly running water, which often is virtually the only aquatic habitat available. These frogs are most diverse in the tropical and subtropical parts of the Oriental region and in sub-Saharan Africa. Most ranids live in forests or along streams, where, because of the longer survival of natural vegetation and rocky shelters than in open areas, the frogs can survive long after deforestation of the surrounding environment. Some ranids occur in savannas, grasslands, or even high-elevation habitats; however, at high elevations they tend to be aquatic, mostly because of the risk of desiccation by wind. Other aquatic ranids, either in lentic (still-water) or in lotic (running-water) habitats, also inhabit tropical and temperate regions, but most of them are primarily terrestrial, staying close to water much of the time or going to water to breed.

Several taxa that undergo direct development do not need free water for breeding and can spend most of their lives away from water; this has allowed them to conquer several rather dry oceanic islands, such as the Solomons. Although many ranids climb on rocks, bushes, or low branches of trees, none are truly arboreal, as are many members of the related Rhacophoridae, which climb and live mostly in trees. Species of Ingerana inhabit rocky cliffs adjacent to cascades, where they live in a permanent mist that provides the moisture necessary for the direct development of their large eggs that presumably are deposited in rock crevices.

Behavior

Most ranids are nocturnal, especially along streams and ponds; thus, they avoid desiccation from sunlight and diurnal predators. Some frogs living close to ponds and lakes, especially in temperate regions, tend to be active by day; they bask in sunlight and periodically enter water. Species living at high elevations also tend to be diurnal, because at night the temperatures may drop too low for them to maintain activity. In tropical forests, ranids feed and breed at night, especially after rains. In savannas and semiarid areas, most species spend the dry season estivating in burrows underground, but a few species concentrate in the few remaining aquatic habitats and may remain active all year round. In humid forests ranids are active most of the year, though breeding is restricted to the rainy periods. In temperate climates, these frogs hibernate either underground or at the bottom of water bodies deep enough to allow the maintenance of a layer of free water below the frozen surface. A few species that occur at high latitudes have antifreeze glycerol-like substances in their tissues.

Territorial behavior is common in ranids. Males of most species call from a permanent site, and they react to the intrusion of another male. The characteristics of the call may change by becoming more aggressive; if the intruder does not leave, physical fighting may ensue (jumping on or biting each other). Some species have hard structures (fanglike odontoids or keratinized spines on the prepollex, fingers, and chest) that may be involved in agonistic behavior. Snakes, birds, and mammals feed on ranids. Large frogs may even feed on smaller ones, including their young, and in natural habitats the young often live in different areas or are not active at the same time as adults, presumably to limit this kind of predation.

Many species are cryptically colored and remain motionless to avoid predation. In several taxa (e.g., Fejervarya and Phrynobatrachus) in which many individuals exist in close proximity around ponds or in grass, color polymorphism (e.g., with or without colored spots, lines, or bands on the dorsum) may create a visual search image for some predators, like birds, so that predation is concentrated for some time on the most common morph. This results in a gradual change in the relative frequencies of morphs over time.

A few large ranids, such as Pyxicephalus, may attack their potential predators or those of their larvae and bite them, but most ranids avoid predation by escape behavior. In species that aggregate around ponds, diving into water often is accompanied by an expulsion of air from the lungs; this alarm or warning call usually prompts nearby individuals to jump into the water. In ponds with soft muddy or sandy bottoms, frogs may hide in the substrate before surfacing, but in streams with nude rocky bottoms devoid of shelters, frogs commonly let the current carry them downstream, where they swim to the bank and remain motionless, protected by their coloration. A few pond-dwelling ranids (Euphlyctis cyanophlyctis and Rana erythraea) can skitter on the surface of water; they may even start from one bank, cross the pond, and jump onto the opposite bank.

Terrestrial frogs (e.g., Ptychadena and Rana sensu stricto) may leap quickly and repeatedly on the ground over several meters without stopping and disappear from sight within a few seconds. Ranid tadpoles usually are swift swimmers and escape predators by dispersing in many directions, sometimes even jumping above the water surface. In a few genera (Aubria and Pyxicephalus), however, tadpoles from the same clutch tend to remain tightly grouped in ball-like schools, which presumably reduces predation.

Feeding ecology and diet

Most ranids are sit-and-wait predators and feed on a wide variety of prey, primarily invertebrates, but the kind of prey depends mostly on the habitats of the frogs. Some terrestrial species tend to move around, both by day and night, likely increasing their chances of finding prey. Large species tend to eat larger prey, including small vertebrates (birds, mammals, reptiles, and other frogs, even their own young). Tadpoles usually feed by rasping food from the substrate with their keratinized mouthparts. Some (Hoplobatrachus) are carnivorous and may feed on heterospecific or conspecific tadpoles.

Reproductive biology

Most ranids have seasonal breeding activity. In temperate climates, breeding usually occurs once a year; in Europe and North America, depending on the species, breeding takes place in early spring, immediately after the melting of ice and snow, or in late spring, when waters are much warmer. In the tropics breeding may happen several times a year, usually at the beginning or end of rainy seasons. In species that breed in standing water (permanent ponds, lakes, or paddy fields) or in temporary waters (marshes or rain pools), calling males aggregate at the breeding site. Choruses may be very loud and audible from considerable distances. Different males often tend to synchronize their calls; if calling is stopped by some perturbation, it is often the same male that reinitiates calling and is followed quickly by the others. Females move to the breeding chorus only when they are ready to ovulate. They may be intercepted on their way to the chorus by peripheral (so-called satellite or parasite) silent males that benefit from the others' calls. In species that breed in lotic aquatic habitats, such as streams or torrents, calling males usually are scattered along the stream, and their calls, which are not synchronized, commonly are sequences of pure notes separated by long intervals.

Amplexus usually is axillary, but in Phrynoglossus it is inguinal. Egg sizes and numbers vary widely and correlate negatively for frogs of the same size. Egg diameter varies from 0.04 in (1 mm) in many small species to 0.2 in (5 mm) in Ceratobatrachus guentheri and eggs number from a few to about 20,000 in Rana catesbeiana. Fertilization is external, except perhaps in some possibly ovoviviparous Limnonectes and in a few poorly known members of the Paini group (Annandia and Ombrana), in which males have a ventrally directed vent surrounded by spines and females have a dorsally directed vent, thus suggesting the possibility of internal fertilization.

Eggs that are deposited in open waters have a pigmented animal pole (brown or black), which probably contributes to their heating and to protection from ultraviolet radiation. Eggs that are hidden under shelters are unpigmented. In some taxa, all ripe eggs are emitted as a single clutch, which is fertilized synchronously by the male, but in other taxa the ovarian complement is partitioned into several clutches deposited at different times in different places. Egg clutches of different females may be grouped together or isolated, often attached to vegetation or as a surface film on water. In temperate regions or at high altitudes, egg clutches are laid preferentially in shallow waters, which are much warmer than the deep parts of the ponds. The eggs of torrent-breeding frogs may be stuck by their jelly under stones or big rocks in a swift-running, richly oxygenated part of the stream. In a few species of the genus Limnonectes, eggs are deposited under decaying vegetation on the forest floor, where the male stays by them for a few days before carrying them to a pool or a stream, a form of behavior resembling larval transport in Dendrobatidae.

A few species build nests for their eggs. In Babina and some species of Nidirana, eggs deposited in water inside nests in paddy fields or marshes hatch as tadpoles. In Anhydrophryne, Arthroleptella, and Taylorana, males dig holes in mud under dead leaves or rocks, where the eggs are deposited and undergo direct development. Other direct-developing ranids deposit eggs in rock crevices (Discodeles and probably Ingerana) or on vegetation above ground (Phrynodon). In the latter genus the female remains near the clutch until the froglets hatch; she sometimes urinates on the eggs, behavior that not only moistens the eggs but also may protect them against fungi and parasites.

Most ranids have aquatic eggs that hatch as free-swimming tadpoles, but direct development has evolved independently in several lineages. Direct development is known in the African Cacosterninae (Anhydrophryne and Arthroleptella) and Petropedetinae (Phrynodon) and in the Asian Dicroglossinae Ceratobatrachini (all five genera) and Limnonectini (Taylorana). It also is suspected in the Asian Batrachylodes. At least one species of Limnonectes in Sulawesi might undergo direct development within the female's genital tract. In some species of Platymantis and Discodeles opisthodon, embryos have several folds on the sides of the belly, which probably serve as respiratory devices, and a hard conical tubercle is present at the extremity of snout, which allows the froglet to pierce the egg capsule at hatching.

Conservation status

According to the IUCN, three species are Extinct: Arthroleptides dutoiti, Rana fisheri, and R. tlaloci. In addition, seven species are Critically Endangered; six are Endangered; 14 are Vulnerable; four are Lower Risk/Near Threatened; and 12 are Data Deficient. Like most anurans, many ranids are threatened with population declines and extinction. Even in pristine national parks in North America, populations of Rana have declined drastically or have become extinct, possibly because of acid rains, increased ultraviolet irradiation, or spreading of pathogens or parasites. Introduction of fishes (especially salmonids) into mountain lakes and even some frogs (such as the aquatic pipid Xenopus) or large ranids (for example, Rana catesbeiana or Hoplobatrachus tigerinus) into fragile ecosystems have had deleterious effects on local populations of many ranids. Capture by humans for frog leg consumption has drastically reduced populations of medium-size to large species in some parts of Europe, northern Africa, and Asia.

Significance to humans

Frog legs have long been considered a delicacy in France, where their consumption used to be a regional and seasonal tradition, linked to the breeding period of brown frogs (Rana temporaria) and green frogs (Pelophylax) in other regions. Subsequent to deep-freezing technology, this consumption has become more widespread, especially in Europe and North America. Because frog "farming" is not profitable, this increased consumption is weighted more and more on natural populations of frogs, especially in southern and southeastern Asia, but several countries now limit this commerce, which is restricted by the Washington Convention for a few ranids. Local consumption by some ethnic groups of whole frogs (not just the legs), often in soups, is a tradition in several tropical countries of Asia and Africa. In southern Africa, adults and larvae of Pyxicephalus are considered a great delicacy. Some species (e.g., members of the genus Paa in the Himalayas or adult males of Elachyglossa in Indochina) are considered to have medicinal value. The use of ranids, especially some European and North American Rana, has contributed greatly to the growth of descriptive and experimental embryology and teratology, and thus to the understanding of the development of vertebrates, and to the perfection of our techniques of intervention in this field.

Species accounts

List of Species

Micro frog

Microbatrachella capensis

subfamily

Cacosterninae

taxonomy

Phrynobatrachus capensis Boulenger, 1910, Cape Flats, Cape Province, Republic of South Africa.

other common names

None known.

physical characteristics

This is one of the smallest anuran species in the world, with a snout-vent length in the adult of 0.4–0.7 in (10–18 mm). The dorsal coloration varies from pale to dark green, gray, fawn, russet, or black, with a dark line from the eye to the armpit, often with a narrow pale or green vertebral stripe, and sometimes with broad lateral stripes or speckles. The dorsum is slightly warty. The ventral surface is smooth, with black and white mottling. Webbing is present but leaves free two or three phalanges of the fourth toe. The male vocal sac extends over half the ventral surface and is blown out almost to the size of the body during call.

distribution

This species exists in the coastal lowlands of southwestern Cape Province, South Africa.

habitat

The frogs live around temporary acidic pools and ponds and in decaying roots.

behavior

Little is known.

feeding ecology and diet

Little is known.

reproductive biology

Males call from half-submerged sites in the marginal vegetation. Calls consist of a series of five to six scratches ("tschik, tschik, tschik"). The very tiny pigmented eggs are deposited in June and July in clusters of about 20, attached to vegetation below the water surface in shallow pools. Benthonic tadpoles have a rather low tail fin and 3/3 tooth rows. They reach 1 in (25 mm) in length, with a tail length of 0.7 in (18 mm). Metamorphosis takes place in December.

conservation status

The species is listed as Endangered according to the IUCN. It is threatened by habitat destruction and pollution over its restricted, and apparently decreasing, range, which covers only a small area of coastal lowlands.

significance to humans

None known.

Faro webbed frog

Discodeles opisthodon

subfamily

Dicroglossinae, tribe Ceratobatrachini

taxonomy

Rana opisthodon Boulenger, 1884, Treasury and Faro Islands, Solomon Islands.

other common names

None known.

physical characteristics

This is a large species, with a snout-vent length reaching 3 in (80 mm) in males and 5 in (125 mm) in females. The skin is smooth or warty, with olive or dark brown coloration on top. The hind limbs are short, the feet are incompletely webbed, and the digital tips are dilated into small discs. The tongue shows a median process. Males have internal vocal sacs.

distribution

This frog lives on the Solomon Islands.

habitat

Little is known.

behavior

Little is known.

feeding ecology and diet

Little is known.

reproductive biology

Eggs, which are very large (at least 0.2 in, or 5 mm, in diameter), are deposited in moist crevices of rocks close to water. Development takes place within these transparent gelatinous balls. The embryos lack tail and gills, but on each side of the abdomen there are several regular transverse folds with a respiratory function. The tip of the snout of these tiny frogs bears a small conical protuberance, projecting slightly through the delicate envelope of the egg and used to perforate this envelope.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Goliath frog

Conraua goliath

subfamily

Dicroglossinae, tribe Conrauini

taxonomy

Rana goliath Boulenger, 1906, Efulen, Cameroon.

other common names

German: Goliatfrosch.

physical characteristics

At 12.6 in (320 mm) in snout-vent length and 7 lb (3.25 kg), this is the largest species of frog still living on our planet. It is dark gray dorsally, with some spots and faintly visible dark bars on the limbs and lips; the ventral coloration is light. The skin on the dorsum and limbs is finely granular. The hind limbs are long, the hand shows slight webbing at the base of the fingers (especially between the first and second), and the foot has complete webbing, without incurvation between the toe tips, which are dilated.

distribution

The distribution of the goliath frog is from southern Cameroon to equatorial Guinea.

habitat

These frogs live in rapids and cascades of rivers in equatorial forest.

behavior

Little is known.

feeding ecology and diet

Little is known.

reproductive biology

Males of this and other species of the genus Conraua are devoid of vocal sacs but have developed a unique mode of calling; they emit long and powerful whistles with the mouth slightly open. Egg masses containing several hundred pigmented eggs, 0.14 in (3.5 mm) in diameter, are attached to plants in rocky pools among the rapids. Tadpoles have 7–8/5–8 tooth rows, numerous papillae, and a low tail fin. They can reach a size of 1.9 in (47 mm). Larval development takes between 85 and 95 days.

conservation status

This species is considered Vulnerable by the IUCN. Recent overharvesting of the species for food, the pet trade, and habitat alteration by humans seem to have reduced the number of populations drastically, and the remainders seem threatened with extinction within a short period of time despite official legal and administrative protection of the species.

significance to humans

These frogs traditionally are hunted as food by the local people, who often approach them by boat on the river and fire at them with guns before they can jump into the water. The species also has been collected live to serve as pets for terrarium keepers in North America.

Indian tiger frog

Hoplobatrachus tigerinus

subfamily

Dicroglossinae, tribe Dicroglossini

taxonomy

Rana tigerina Daudin, 1802, Bengal, India.

other common names

English: Indian bullfrog, tiger Peters frog; German: Tiger-frosch, Asiatischer Ochsenfrosch.

physical characteristics

This is a large frog species, with a snout-vent length up to 4.3 in (110 mm) in males and 6.3 in (160 mm) in females. The frogs have greenish coloration, longitudinal skin folds on the dorsum, and strong hind limbs with large webbing. Males show nuptial pads on the first finger and vocal sacs on both ventral sides of the throat, forming bluish longitudinal folds.

distribution

This frog occurs in Bangladesh, Bhutan, India, Myanmar, Nepal, and Pakistan; it was introduced into Madagascar.

habitat

The species lives around ponds and in paddy fields.

behavior

Little is known.

feeding ecology and diet

Little is known.

reproductive biology

At the beginning of the monsoon, breeding males, which have bright yellow coloration, gather around standing waters, where they emit loud calls that attract females. The pigmented eggs are small and numerous. Tadpoles show very strong jaw sheaths and have 3–4/4–5 double tooth rows; they are carnivorous.

conservation status

This species is not listed by the IUCN. However, overexploitation of this species for frog leg consumption has resulted in steep declines in populations, especially in northern India, which has resulted in a striking increase in pest populations in paddy fields. Recent legal protection of this species has limited this decline, though it has not suppressed it entirely.

significance to humans

None known.

Penang Taylor's frog

Taylorana hascheana

subfamily

Dicroglossinae, tribe Limnonectini

taxonomy

Polypedates hascheanus Stoliczka, 1870, Penang Island, Malaysia.

other common names

None known.

physical characteristics

This is a small species, reaching 1.5 in (37 mm) in snoutvent length. It is yellow, orange, or brown dorsally, with dark brown spots and a mid-dorsal chevron, sometimes with a yellow vertebral streak. The extremities of the digits are dilated into small discs with dorsoterminal grooves. The feet are poorly webbed. The male is devoid of nuptial pads and vocal sacs but has a pair of fanglike odontoids on the lower jaw.

distribution

This species is found in Cambodia, Laos, Malaysia, Thailand, and Vietnam.

habitat

The frog inhabits the forest floor, often close to small rivers.

behavior

Little is known.

feeding ecology and diet

Little is known.

reproductive biology

Males dig holes in the mud under dead leaves, from where they emit isolated short notes ("kra") of 250–400 msec, separated by silences of 30 sec to several minutes. Females meet them in these "nests," where they deposit five to 13 large whitish eggs (0.12 in, or 3 mm, in diameter). The complete development takes place within the egg, from which tiny froglets emerge about one month after egg laying.

conservation status

Not listed by IUCN.

significance to humans

None known.

Spiny-armed frog

Paa liebigii

subfamily

Dicroglossinae, tribe Paini

taxonomy

Rana liebigii Günther, 1860, Nepal.

other common names

None known.

physical characteristics

This is a large species, with a snout-vent length up to 4.6 in (117 mm). The frog is brown, yellow, reddish, or blackish in color, with long hind limbs and well-developed, but incomplete webbing. The iris is bright gold, with a horizontal and a vertical dark line forming a cross in the eye. Breeding adult males have very large forelimbs and large black spines on the prepollex, the first three fingers, the arm, the forearm, and both sides of the breast.

distribution

This species exists in Bhutan, western China (Xizang), northern India, and Nepal.

habitat

These frogs live along torrents from 5,000 ft (1,520 m) to 11,500 ft (3,510 m) in forested and nonforested areas.

behavior

Little is known.

feeding ecology and diet

Little is known.

reproductive biology

Breeding males call at night from below rocks or from the banks of fast-running torrents. Their call consists of a long (2.3–4.6 sec) series of 15–27 pure notes separated by long silences (10.1–37.2 sec), which are easier for females to locate than continuous noisy calls would be. Amplexus and egg deposition take place below rocks in oxygenated parts of the torrent. The eggs are large (0.2 in, or 5 mm, in diameter) and only slightly colored at the animal pole; inside, a sticky jelly maintains them attached to rocks in the current. The tadpoles have strong tail muscles, low tail fins, and 3–6/3 tooth rows.

conservation status

Not listed by IUCN.

significance to humans

In central Nepal, women eat females of this species to relieve abdominal pain.

Corrugated water frog

Lankanectes corrugatus

subfamily

Lankanectinae

taxonomy

Rana corrugata Peters, 1863, Sri Lanka.

other common names

None known.

physical characteristics

This is a stout, medium-size species, with a snout-vent length up to 2.6 in (65 mm). The hind limbs are short and thick, with broad but not complete webbing and slightly dilated tips. The dorsal coloration is brown or brownish orange with dark spots. The dorsal parts of the head and body are covered with a network of ridges, and the larval lateral-line system persists in adults. Adult males have odontoid fangs on the lower jaw and internal vocal sacs.

distribution

This species is found in Sri Lanka.

habitat

These frogs live along shaded, slow-flowing streams and marshes in forested areas at elevations of 200–5,000 ft (60–1,525 m).

behavior

Little is known.

feeding ecology and diet

Little is known.

reproductive biology

Males of this species emit dull advertisement calls ("urrm") that can be heard from several meters in the forest habitat. Tadpoles have 2/3 tooth rows and are 1 in (26 mm) long when the hind limbs are fully developed.

conservation status

Not listed by IUCN.

significance to humans

None known.

Nilgiri tropical frog

Micrixalus phyllophilus

subfamily

Micrixalinae

taxonomy

Limnodytes phyllophila Jerdon, 1853, Nilgiris, southern India.

other common names

None known.

physical characteristics

This small species (1.25 in or 3.175 cm long) is brownish, with smooth dorsal skin and narrow dorsolateral folds. The hind part of the abdomen and the lower side of the legs are rose colored. Vomerine teeth are absent; the tongue bears a median process. The hind limbs are of medium length, the toes are nearly entirely webbed, and the digital tips bear small discs. The males have internal vocal sacs and nuptial pads.

distribution

This species ranges across southern India.

habitat

The frogs inhabit evergreen hill forests.

behavior

Little is known.

feeding ecology and diet

Little is known.

reproductive biology

The body of the tadpole is elongated and depressed, with a long and slender tail and low fins. The subterminal mouth bears many papillae and stout jaw sheaths, but there is only a single row of poorly developed teeth on the upper jaw.

conservation status

Not listed by IUCN.

significance to humans

None known.

Malabar night frog

Nyctibatrachus major

subfamily

Nyctibatrachinae

taxonomy

Nyctibatrachus major Boulenger, 1882, Malabar and Wynaad, southern India.

other common names

None known.

physical characteristics

This medium-size, stout species has a snout-vent length up to 2.1 in (53.6 mm). The dorsal coloration varies from light tan to dark brown, with indistinct markings. The pupil is vertical. The limbs are short and the feet nearly entirely webbed; the digital tips have discs bearing dorsoterminal folds. Adult males have well-developed femoral glands, internal vocal sacs, and nuptial pads.

distribution

The species ranges across southern India.

habitat

This frog lives in and beside rocky hill streams at medium elevations, 360–3,020 ft (110–920 m).

behavior

Little is known.

feeding ecology and diet

Little is known.

reproductive biology

Eggs have pigmented animal poles. Tadpoles are devoid of tooth rows but have jaw sheaths and numerous papillae.

conservation status

Not listed by IUCN.

significance to humans

None known.

Pointed-tongue floating frog

Occidozyga lima

subfamily

Occidozyginae

taxonomy

Rana lima Gravenhorst, 1829, Java, Indonesia.

other common names

English: Java frog.

physical characteristics

This small frog has a maximum size of 1.5 in (39 mm). The skin is very rough, and there is persistence of the lateral-line system in the adult. The dorsum is dark olive with dark spots and sometimes a mid-dorsal line; the rear parts of the thighs show two longitudinal dark lines enclosing a longitudinal white line. The tongue is pointed behind, and there are no vomerine teeth. The extremities of the digits are pointed, and webbing of the feet is complete. Males have nuptial pads and internal vocal sacs.

distribution

The frog occurs in southern China, Indochina, Indonesia, and Malaysia.

habitat

These frogs live in ponds, marshes, and paddy fields, where they seldom leave water.

behavior

Little is known.

feeding ecology and diet

Little is known.

reproductive biology

Males emit calls composed of two short notes. Amplexus is axillar. The eggs are small and pigmented, and the tadpole is elongated (up to 1.3 in, or 33 mm), with a pointed snout and tail tip and a high crest on the anterior tail fin. The tadpole's mouth is small, without papillae, tooth rows, or upper jaw sheath but with a horseshoe-shaped lower jaw sheath.

conservation status

Not listed by IUCN.

significance to humans

None known.

Sanderson's hook frog

Phrynodon sandersoni

subfamily

Petropedetinae

taxonomy

Phrynodon sandersoni Parker, 1935, Cameroon.

other common names

None known.

physical characteristics

This is a small species, with a snout-vent length up to 0.9 in (22 mm) in males and 1 in (26 mm) in females. The frogs have trapezoidal enlarged digital tips and femoral glands. The dorsal coloration varies widely, from translucent yellow to brownish; the lower parts are lemon yellow. Males are devoid of nuptial pads but have internal vocal sacs and odontoid fangs on the lower jaw.

distribution

The frogs exist in Cameroon, Fernando Póo, and West Africa.

habitat

This species inhabits hilly equatorial forest.

behavior

Little is known.

feeding ecology and diet

Little is known.

reproductive biology

Males are territorial and will bite intruder males in their territory. Eggs are laid on the leaves of small trees, bushes, or herbaceous plants, up to 6.6 ft (2 m) above a very humid substrate. Each clutch counts 12–17 eggs that are each 0.09 in (2.3 mm) in diameter. The female remains in the vicinity of the eggs during daylight hours and climbs on them every evening to spend the night over them. After 12 days of development, the tadpoles, which are curved narrowly within the egg's capsule, are "ejected" from the eggs. They are devoid of jaw sheaths and tooth rows, and they do not feed until metamorphosis, living on their vitelline reserves. Small froglets with fully resorbed tails develop about six weeks after egg laying.

conservation status

Not listed by IUCN.

significance to humans

None known.

Sharp-nosed grass frog

Ptychadena oxyrhynchus

subfamily

Ptychadeninae

taxonomy

Rana oxyrhynchus Smith, 1849, Natal, South Africa.

other common names

None known.

physical characteristics

This is a medium-size species, with a snout-vent length up to 2.3 in (58 mm) in males and 2.7 in (68 mm) in females. The snout is long, and the dorsum is brownish with dark spots on strongly elevated skin ridges. The hind limbs are very long, with large webbing. Males have nuptial pads and vocal sacs that protrude through lateral slits.

distribution

These frogs exist in most of sub-Saharan Africa.

habitat

The species inhabits forests and nearby savannas.

behavior

Little is known.

feeding ecology and diet

Little is known.

reproductive biology

Males emit intense, high-pitched thrills of about 0.4 sec, which are repeated every second. Tadpoles have 2/2 tooth rows.

conservation status

Not listed by IUCN.

significance to humans

None known.

African bullfrog

Pyxicephalus adspersus

subfamily

Pyxicephalinae

taxonomy

Pyxicephalus adspersus Tschudi, 1838, Cape of Good Hope, South Africa.

other common names

English: Giant pixie; German: Gruener Grabfrosch.

physical characteristics

This is a large, toadlike species; males have a snout-vent length up to 9 in (230 mm) and a weight up to 2.4 lb (1.075 kg). Males are larger than females. Adults are olive green and juveniles are bright green, with longitudinal skin folds on the dorsum, short legs, and a shovel-shaped inner metatarsal tubercle. Odontoid fangs are present on the lower jaw.

distribution

The species' range is southern Africa.

habitat

This frog inhabits open grass or bush country.

behavior

These frogs estivate underground in a cocoon made of layers of molted skin. They emerge after heavy rains to breed.

feeding ecology and diet

These frogs are omnivorous. Because of their large size and aggressive habits, they can feed on vertebrates (mammals, birds, snakes, lizards, and frogs, including their own young or even other adults).

reproductive biology

Males gather in daylight in shallow temporary pools, where they emit their loud "whoop, whoop," which recalls the lowing of cattle. Males usually fight among themselves, frequently wounding each other with their odontoids. Dominant males may fertilize the eggs of several females in their territory. Females lay 3,000–4,000 pigmented eggs that are each 0.08 in (2 mm) in diameter. Tadpoles with 4–5/3 tooth rows may reach a size of 2.8 in (71 mm). They swim together in schools of up to 3,000, attended by the father. The father can attack and bite potential predators (including lions or humans) or dig channels 49 ft (15 m) long or more, allowing tadpoles that have become isolated in peripheral puddles to return to the main pond. Metamorphosis usually takes place very quickly (as little as 18 days after egg laying). Froglets may eat each other.

conservation status

Not listed by IUCN.

significance to humans

From prehistoric times to the present, adults, young, and tadpoles have been eaten by various peoples in Africa.

Beautiful torrent frog

Amolops formosus

subfamily

Raninae, tribe Amolopini

taxonomy

Polypedates formosus Günther, 1876, Khasi Hills, Assam, India.

other common names

English: Assam sucker frog.

physical characteristics

This is a medium-size species, with a snout-vent length up to 3.3 in (85 mm). The frogs have a bright green, greenish, or olive dorsum covered with spots. The dorsal and ventral skins are smooth; dorsolateral folds are absent. The hind limbs are very long, with complete webbing. The digital tips bear large discs with ventrolateral grooves. Adult males have vocal sacs and velvety nuptial pads on the first finger.

distribution

The species' range is Bhutan, northern India, and Nepal.

habitat

The frogs live along torrents from 5,640 ft (1,720 m) to 8,700 ft (2,650 m) in forested and nonforested areas.

behavior

Little is known.

feeding ecology and diet

Little is known.

reproductive biology

Males call from the banks or rocks along or in torrents. Eggs, which are ivory white, are stuck by their jelly under rocks or stones in the rapid part of the torrent. Tadpoles are gastromyzophorous, that is, they have a large sucker that covers the anterior part of the belly and numerous tooth rows (6–7/3).

conservation status

Not listed by IUCN.

significance to humans

None known.

Bullfrog

Rana catesbeiana

subfamily

Raninae, tribe Ranini

taxonomy

Rana catesbeiana Shaw, 1802, North America.

other common names

French: Grenouille taureau (France), Ouaouaron (Quebec); German: Nordamerikanischer Ochsenfrosch; Spanish: Rana toro americana, rana mugidora.

physical characteristics

This member of the subgenus Aquarana is the largest North American frog, reaching 8 in (203 mm) and more than 3.3 lb (1.5 kg). It is greenish, olive, or brownish, sometimes with darker spots on the back. The tympanum is large, especially in males, and there are no dorsolateral folds. The hind limbs are long and the feet fully webbed. Males have nuptial pads, single internal vocal sacs, and yellowish throats.

distribution

The species inhabits eastern North America from Mexico to southern Canada. It was introduced into western North America, Central and South America, the West Indies, Japan, China, Thailand, several European countries, and several oceanic islands.

habitat

This semiaquatic frog can be found in many habitats, though it prefers larger bodies of water than most other frogs.

behavior

Bullfrogs prefer warmer weather, digging into the mud to hibernate during cold winter weather. Adult males are aggressive and defend their shoreline territories by wrestling with other male bullfrogs.

feeding ecology and diet

Rather than actively hunting, bullfrogs wait for their prey to come to them. They eat others of their own species, frogs and tadpoles, snakes, insects, worms, and crustaceans.

reproductive biology

After hibernation, males gather to emit their low, guttural calls composed of long notes. They are territorial and aggressive. Eggs, which are 0.05–0.07 in (1.2–1.7 mm) in diameter and pigmented at the animal pole, are laid in groups of 3,000–20,000. Tadpoles have 2–3/3 tooth rows and attain lengths up to 6.7 in (170 mm) before metamorphosis, which may occur after two to four years in northern latitudes (Quebec, Canada).

conservation status

Not listed by IUCN.

significance to humans

This frog is consumed by humans and is used for dissection in colleges and universities. It has been introduced into a variety of regions all around the world, often with success; many of these introduced populations have had dramatic negative impacts, through competition and direct predation, on the local fauna. Because of its high level of fertility, eradication of the species once it is established in a new habitat is difficult, if not impossible.

Roesel's green frog

Rana esculenta

subfamily

Raninae, tribe Ranini

taxonomy

Rana esculenta Linnaeus, 1758, Nürnberg, Germany.

other common names

English: Edible frog; French: Grenouille verte; German: Teichfrosch Wasserfrosch.

physical characteristics

This is the common green frog that appears in many textbooks as well as in comics and children books. It is about 2.4–3.5 in (60–90 mm) in snout-vent length. Typically, this frog is green or greenish, though sometimes other colors (brownish, grayish) are seen; there are a varying numbers of spots on the back. The frog has rather long hind limbs, and its feet are almost fully webbed. In several characters, this form is intermediate between the two species from which it originated by hybridization: Rana lessonae (which is smaller, with shorter hind limbs and a short, shovel-shaped internal metatarsal tubercle) and Rana ridibunda (which is larger, with longer hind limbs and a long and flat internal metatarsal tubercle). Males have nuptial pads and white external vocal sacs that protrude during calling through slits on the sides of the mandible close to the mouth commissure.

distribution

The species is distributed throughout Europe.

habitat

This frog lives in open habitats around medium-size or large ponds and lakes, and less often close to small ponds or along rivers.

behavior

This frog is semiaquatic and seldom goes far from water except on rainy nights, when it may colonize new habitats. It is active both during the day and at night. It has complex social structures, behaviors, and vocal repertoires, especially since it shares its habitat with at least one of its parental species.

feeding ecology and diet

Little is known.

reproductive biology

This form is not properly a species but a "stabilized hybrid," or klepton (which may be indicated by inserting "kl." before its "specific" name), that shows a modified meiosis known as hybridogenesis. As a result, the frogs produce pure gametes containing the chromosomes from only one of their original parental species, that is, either Rana lessonae or R. ridibunda; they breed with the opposite species, and, thus, individuals identical to first-generation hybrids are produced again at each generation. This frog breeds in late spring or early summer (April–June). Males gather in breeding leks, where they emit loud calls and where they are joined by females that are ready to lay eggs. Females lay 2,000–6,000 pigmented eggs that are 0.04–0.06 in (1–1.5 mm) in diameter. Tadpoles have high tail fins and 2/3 tooth rows, and they are swift swimmers. They usually reach a size of 1.6–1.77 in (40–45 mm) and metamorphose in late summer; occasionally, they hibernate and reach giant sizes of 3.5–4.7 in (90–120 mm).

conservation status

This species is not listed by the IUCN. However, because of frog consumption, many populations of this frog have been drastically reduced.

significance to humans

The legs of this frog traditionally have been eaten in Europe, especially in France. Apart from this economic function, this frog is particularly significant to humans as basic research material. Despite its having been used for many years in innumerable experimental works in various fields of biology (among them, physiology, embryology, teratology), it was only in the 1960s that the extraordinary nature of this "species" was suspected and later established. Several kleptons exist among European green frogs (subgenus or genus Pelophylax), but in all cases one of the two parental species is Rana ridibunda. This phenomenon is still largely misunderstood, and research on this frog complex remains promising for the understanding of basic aspects of cell physiology and vertebrate sexuality. Other unresolved research topics related to these frogs include the massive anomalies affecting the limbs of high percentages of frogs in some populations, which have been studied for more than half a century but remain a mystery.

Brown frog

Rana temporaria

subfamily

Raninae, tribe Ranini

taxonomy

Rana temporaria Linnaeus, 1758, Sweden.

other common names

English: European common frog, grass frog; French: Grenouille rousse; German: Grasfrosch; Spanish: Rana roja, rana bermeja.

physical characteristics

This is the most common European species of the group of brown frogs, the distribution of which covers most of Europe from sea level in the north to above 6,562 ft (2,000 m) in the south. Over this vast area, the species shows considerable variety in most characters, and several subspecies have been recognized. It is 2.4–3.7 in (60–95 mm) in snout-vent length and displays a vast array of colorations, including brown, reddish, orange, yellow, olive, gray, and blackish; none is green. The dorsum is more or less spotted, the legs are barred, and the eye coloration varies considerably, with a basic golden iris, which may be more or less charged in melanophores. The hind limbs are short but may be longer in some southern populations or regions. The webbing is usually large but is less developed in Iberian populations. Males have nuptial pads and internal vocal sacs, and their throats are bluish during the breeding period.

distribution

The species is distributed throughout Europe.

habitat

This frog occurs in forest habitats and grasslands. At high elevations and latitudes, it lives in meadows, marshes, and peat bogs.

behavior

This frog spends most of its life on the forest floor or in the grass, but it moves to ponds for breeding. In mountain habitats it may remain around ponds or lakes for most of the year.

feeding ecology and diet

Little is known.

reproductive biology

This species breeds as soon as snow and ice melt, at widely different periods according to elevation and latitude. Males gather for calling, and egg masses often are grouped by the dozens or hundreds in shallow parts of the ponds. Each female lays 1,000–4,000 eggs that are each 0.08–0.12 in (2–3 mm) in diameter. Tadpoles, which have 3–4/4 tooth rows, may reach a length of 1.77 in (45 mm) before metamorphosis.

conservation status

This species is not listed by the IUCN. However, in several countries, and especially in mountain areas, commercial exploitation of these frogs for human consumption has had drastic negative impacts on the populations.

significance to humans

This species is eaten by Europeans.

Beddome's Indian frog

Indirana beddomii

subfamily

Ranixalinae

taxonomy

Polypedates beddomii Günther, 1876, Anamallays, Malabar, Sevagherry and Travancore, India.

other common names

None known.

physical characteristics

This medium-size species has a snout-vent length up to 2 in (49.5 mm) in males and 2.4 in (60.1 mm) in females. The dorsal skin is covered with short longitudinal glandular folds. The coloration varies; it can be yellowish, pinkish, or brownish, with irregular speckling. The hind limbs are long, the webbing is incomplete, and the tips of the digits are dilated into discs. Adult males have large tympana, vocal sacs, nuptial pads, and femoral glands.

distribution

The species is distributed throughout southern India.

habitat

The frogs inhabit the forest floor or rocky soil in evergreen forest at 330–2,950 ft (100–900 m).

behavior

Little is known.

feeding ecology and diet

Little is known.

reproductive biology

Pigmented eggs presumably are deposited outside water under shelters, such as stones, rotten vegetation, or the bark of dead trees. Tadpoles are peculiar, with an elongated body form, extremely large eyes, and a slender and pointed tail. The hind limbs develop early, and they have 4–5/4 tooth rows. From the beginning they can use their tails, and later their hind limbs, to skitter on the rocks or ground, which allows them to go from one humid terrestrial shelter or shallow pool to another.

conservation status

Not listed by IUCN.

significance to humans

None known.

Resources

Books

Duellman, William E., and Linda Trueb. Biology of Amphibians. New York: McGraw-Hill, 1986.

Passmore, N. I., and V. C. Carruthers. South African Frogs: A Complete Guide. Revised edition. Johannesburg, South Africa: Witwatersrand University Press, 1995.

Periodicals

Blommers-Schlösser, R. M. A. "Systematic Relationships of the Mantellinae Laurent, 1946 (Anura, Ranoidea)." Ethology, Ecology, and Evolution 5 (1993): 199–218.

Bossuyt, F., and M. C. Milinkovitch. "Convergent Adaptive Radiations in Madagascan and Asian Ranid Frogs Reveal Covariation between Larval and Adult Traits." Proceedings of the National Academy of Sciences of the United States of America 97 (2000): 6585–6590.

Clarke, B. T. "Comparative Osteology and Evolutionary Relationships in the African Raninae (Anura Ranidae)." Monitore Zoologico Italiano (new series), supplement 15 (1981): 285–331.

Dubois, A. "Liste des Genres et Sous-genres Nominaux de Ranoidea (Amphibiens, Anoures) du Monde, avec Identification de Leurs Espèces-types: Conséquences Nomenclaturales." Monitore Zoologico Italiano (new series), supplement 15 (1981): 225–284.

——. "Notes sur la Classification des Ranidae (Amphibiens, Anoures)." Bulletin Mensuele de la Société Linnéenne de Lyon 61, no. 10 (1992): 305–352.

Emerson, S. B., R. F. Inger, and D. Iskandar. "Molecular Systematics and Biogeography of the Fanged Frogs of Southeast Asia." Molecular Phylogenetics and Evolution 16 (2000): 131–142.

Kosuch, J., M. Vences, A. Dubois, A. Ohler, and W. Böhme. "Out of Asia: Mitochondrial DNA Evidence for an Oriental Origin of Tiger Frogs, Genus Hoplobatrachus." Molecular Phylogenetics and Evolution 21 (2001): 398–407.

Marmayou, J., A. Dubois, A. Ohler, E. Pasquet, and A. Tillier. "Phylogenetic Relationships in the Ranidae: Independent Origin of Direct Development in the Genera Philautus and Taylorana." Comtes Rendus de l'Académie de Sciences Paris 323 (2000): 287–297.

Ohler, A., and A. Dubois. "Démonstration de l'Origine Indépendante des Ventouses Digitales dans Deux Lignées Phylogénétiques de Ranidae (Amphibiens, Anoures)." Comtes Rendus de l'Académie de Sciences Paris 309 (1989): 419–422.

Vences, Miguel, and F. Glaw. "When Molecules Claim for Taxonomic Changes: New Proposals on the Classifcation of Old World Treefrogs." Spixiana 24, no. 1 (2001): 85–92.

Vences, Miguel, Stefan Wanke, Gaetano Odierna, Joachim Kosuch, and Michael Veith. "Molecular and Karyological Data on the South Asian Ranid Genera Indirana, Nyctibatrachus and Nannophrys (Anura: Ranidae)." Hamadryad 25, no. 2 (2000): 75–82.

Alain Dubois, Docteur d'Etat