Narrow-mouthed frogs

(Microhylidae)

Class Amphibia

Order Anura

Family Microhylidae

Thumbnail description
Tiny to medium-size frogs with a broad spectrum of morphologic features

Size
0.5–4 in (11.5–100 mm)

Number of genera, species
67 genera; 362 species

Habitat
Forest, woodlands, scrub, savanna, grassland, semidesert

Conservation status
Endangered: 2 species; Vulnerable: 6 species; Data Deficient: 3 species

Distribution
The eastern to southwestern United States southward through much of South America; sub-Saharan Africa, Madagascar, most of India, Sri Lanka, and Southeast Asia to extreme northern Australia

Evolution and systematics

It scarcely has been questioned that the Microhylidae family constitutes a natural group most closely related to others among the ranoid frog families, such as the Ranidae, Rhacophoridae, and Hyperoliidae. Characterizing the family proves elusive, however. Definitions always include the unique character of serrated, transverse folds of skin on the palate, but some species lack these features or have them in reduced numbers and sizes. Emphasis always is placed on a distinctive suite of larval characters, though almost 30% of the genera and nearly half the species of microhylids undergo direct embryonic development, skipping a free-living larval stage. Where there are free-swimming, feeding larvae, they typically lack the cornified denticles ("teeth") and beak seen in larvae of other families and have a median, ventral spiracle (the opening through which water taken in through the mouth is discharged) rather than one on the left side. Here again there are exceptions.

The fossil record of the Microhylidae is meager, but if the assignment of fossils from the Miocene of Florida (about 24 million years ago) to the present-day genus Gastrophryne is accurate, it speaks to a moderately long history. The presence of Microhylidae in South America, Africa, Madagascar, India, and Australia strongly suggests a Gondwanan origin. If this is correct, the abundance of microhylids in Southeast Asia, reaching as far as Korea, remains to be explained, as does their restriction to northern Australia. One scenario has primitive microhylids riding northward on the drifting Indian subcontinent, thereby gaining access to Asia and, eventually, New Guinea and Australia. Alternatively, they could have accompanied Australia on its northward journey, spreading to New Guinea and the East Indies as those more recent terrains emerged. Until a better understanding of relationships among the microhylid families is gained, the zoogeography of the Microhylidae will remain enigmatic.

A monograph of the family Microhylidae by H. W. Parker, published in 1934 and still the only family-wide treatment, was conservative in outlook; subsequent research has increased greatly the recognized number of genera and species. In 1954 Antenor Leitão de Carvalho published the first modern treatment of the American genera of microhylids. A phylogenetic arrangement of the New World microhyline genera presented by Zweifel in 1986 was refined by Donnelly, de Sá, and Guyer in 1990 and again by Wild in 1995. The Aster-ophryinae received similar attention from Zweifel in 1972 and Burton in 1986.

Relationships among the microhylid subfamilies and their genera are not well worked out. The presence of maxillary and vomerine teeth together with the retention of clavicles and procoracoid cartilages in the genera Dyscophus (Dyscophinae) and Platypelis (Cophylinae) mark these Malagasy frogs as primitive with respect to other microhylids. No firm line of relationship has been drawn, however, to other subfamilies. Relationships among the African and Asiatic microhylines have not been investigated.

Nine subfamilies are recognized; the Scaphiophrynidae of Madagascar formerly was placed as a subfamily but is now recognized as a separate family.

Asterophryinae

The vertebral column is diplasiocelous: all vertebrae are procelous (concave anteriorly, convex posteriorly) except the eighth, which is opisthocelous (convex anteriorly, convex posteriorly). There are no teeth, and the tongue is largely adherent behind. The maxillary bones tend to meet in front of the premaxillary bones or overlap them, and the pectoral girdle lacks clavicles and procoracoid cartilages. The latter are paired elements of the pectoral girdle present in the majority of frogs. All species undergo direct embryonic development. The distribution is confined to New Guinea and the Moluccas. There are eight genera with 54 species.

Brevicipitinae

The vertebral column is diplasiocelous, and there are clavicles and procoracoid cartilages. This subfamily has no teeth. The vomerine bones, paired elements in the roof of the mouth, are large, with a median expansion. Tadpoles are not free swimming. These frogs occur wholly in Africa, from Ethiopia to the Cape of Good Hope. There are five genera with 19 species.

Cophylinae

The vertebral column is procelous; there are procoracoids, but there may or may not be clavicles. This subfamily has maxillary or vomerine teeth or both. Four of the genera lack the transverse palatal folds found in almost all other micro-hylids. The distribution is restricted to Madagascar. There are seven genera with 35 species.

Dyscophinae

The vertebral column is diplasiocelous; clavicles and procoracoids typically are present, but they are absent in one species. The anterior median element of the pectoral girdle, the omosternum, is bony (which is unique within the Micro-hylidae) or cartilaginous. This subfamily has maxillary and vomerine teeth. The distribution is broadly disjunct, with one genus (Dyscophus, three species) in Madagascar and one genus (Caluella, six species) in Madagascar and Asia. Their supposed evolutionary relationship is based largely on shared primitive characters that are not phylogenetically informative, and it deserves to be reassessed.

Genyophryninae

The vertebral column is procelous; maxillary bones over-lap the premaxillae only slightly. The pectoral girdle may lack clavicles and procoracoids, may have both, or may have only procoracoids. Teeth usually are lacking, but vestiges may be present on the maxilla; the tongue is at least one-fourth free behind. All species undergo direct embryonic development. The distribution is concentrated in New Guinea, with fringe species in the southern Philippines, Sulawesi, the Lesser Sunda Islands, New Britain, and northern Australia. There are 11 genera and 118 species, more species than in any other subfamily.

Melanobatrachinae

The vertebral column is procelous; there are no clavicles, and the procoracoids may be present or vestigial. This sub-family lacks a tympanum (eardrum) and teeth. Tadpoles are not free swimming. The distribution is discontinuous; the genera are dispersed between eastern Africa (Tanzania: two genera, with three species) and India (one monotypic genus).

Microhylinae

The vertebral column is diplasiocelous (rarely procelous); the pectoral girdle may lack clavicles and procoracoids, may have both, or may have only procoracoids. There are no teeth. Vomers typically are present in separate anterior and posterior locations, but they may be absent posteriorly. Most species typically have free-swimming microhylid larva lacking cornified denticles and beak. The distribution is widespread; this is the only microhylid family in the New World apart from the Otophryninae, and it also ranges from eastern Pakistan, Sri Lanka, and India to China, Korea, the Ryukyu Islands, and into the Southeast Asian archipelago. There are 29 genera, with 115 species (second only to the Genyophryninae).

Otophryninae

The vertebral column is diplasiocelous, and there are clavicles and procoracoids. The larval spiracle is on the left side rather than median, and extends posteriorly as a tube as the tadpole grows. The larvae have dagger-like, keratinized teeth. This subfamily is distributed in northern South America from southeastern Colombia to the extreme northeast of Brazil. There is one genus, with three species. The recognition of the Otophryninae as a taxon distinct from the Microhylinae is questioned by some researchers.

Phrynomerinae

The vertebral column is diplasiocelous; procoracoids and clavicles are absent. A pad of cartilage (the intercalary cartilage) separates the distal two phalanges of each finger and toe. Tadpoles are the typical, free-swimming microhylid sort. The subfamily is wholly African in distribution, found from western Africa to Somalia and South Africa. There is one genus, with five species. The Phrynomerinae once held family status, but only the phalangeal character distinguishes Phryno-mantis from other microhylids.

Physical characteristics

Narrow-mouthed frogs have no external physical characteristics that enable a person with a living frog in hand, but no other pertinent information, to identify it as a micro-hylid. Most genera of microhylids have two or three serrated folds across the palate (a feature unique to this family) and lack teeth. The pectoral girdle always has coracoid bones that meet on the midline (the so-called firmisternal condition) but often shows reduction or absence of other ventral elements. Clavicles may be as small as tiny slivers of bone or may be lacking, and the procoracoid cartilage may be absent. The omosternum (which is not always present) is, with one exception, cartilaginous rather than bony. Species with exceptions to some of these characters are presumably primitive forms in Madagascar that have teeth, lack the palatal folds, and show minimal reduction of elements of the pectoral girdle.

There are few large microhylids. Only about 8% of the species have a body length as great as 2.4 in (60 mm), whereas about 83% attain a length of less than 2 in (50 mm). A few are less than 0.5 in (13 mm) when they reach adulthood. Microhylids have adapted to a wide variety of habitats and consequently show diverse body forms. One of the most common is a teardrop shape with chunky body and narrow head ending in a pointed snout. This habitus is responsible for the name narrow-mouthed frogs, but the appellation is inappropriate for many microhylid genera. Some microhylids are true treefrogs with large eyes and expanded terminal disks on the fingers and toes that facilitate climbing. Terrestrial species include squat, small-eyed, short-legged frogs that spend most of their time in burrows or hidden in leaf litter and other, more svelte and agile forms that live in and on the forest floor amid leaf litter.

Microhylids typically are drab-colored frogs with shades of brown and dull yellow dominating dorsally; the undersides may be brighter. Species of rubber frogs (genus Phrynomantis) in southern Africa are exceptions; they have bright-red dorsal markings on a black or brown background. This may be a warning coloration, as at least one species produces toxic skin secretions.

Distribution

Most of the geographic range of the Microhylidae lies between the Tropics of Cancer and Capricorn, with a few species exceeding these limits in North America, South America, southern Africa, and Southeast Asia. In addition to these continental distributions and their presence in the East Indies, Philippines, and northern Australia, microhylids are an important component of the frog faunas of the large tropical islands of Madagascar and New Guinea.

Habitat

Microhylids occupy diverse habitats ranging in elevation from sea level to about 13,000 ft (4,000 m). A majority of species dwell in tropical rainforests, occupying a variety of ecological niches. Some live in burrows in the soil, from which they emerge to feed or find mates; others seem to stay largely within the shelter of the forest floor amid leaf litter. Climbing species may ascend low shrubbery at night, but more arboreal varieties may spend their entire lives high in the trees. A small number of species (genera Oreophryne and Oxydactyla) inhabit alpine grassland at elevations of more than 12,000 ft (3,700 m) in New Guinea. Temperate regions apparently lack arboreal microhylids, but frogs nevertheless range through terrestrial habitats from moist lowland forests to nearly desert conditions. Rain frogs (genus Breviceps) in southern Africa even burrow in sand dunes. Although aquatic habitats serve as breeding sites for many microhylid species and there are a few riparian species, no microhylid is known to be primarily aquatic.

Behavior

Given their wide range of habitats and diversity of body forms, microhylids would be expected to show a variety of adaptive behaviors, and indeed they do. Some terrestrial species have flattened, projecting "spades" on the heels that facilitate burrowing backward into the soil with a shuffling motion. Others lack these structures and burrow headfirst. Defensive activity is usually "leap and hide"—that is, dive underwater or burrow into surface litter—which is characteristic of frogs in general. A broad-headed frog of New Guinea,

Asterophrys turpicola, takes the offensive when disturbed. It faces a potential predator with its body inflated and its mouth gaping, displaying a bright blue tongue; then it bites and holds on. If attacked, the Madagascar tomato frog (Dyscophus antongilii) can produce slime so sticky that a small predator trying to eat it could find its eyelids and lips stuck together. In its adhesive properties, the slime is nearly five times stronger than rubber cement! The Great Plains narrow-mouthed toad (Gastrophryne olivacea) in the United States and a South American species, the dotted humming frog (Chiasmocleis ventrimaculatus), sometimes live with and are not attacked by tarantulas in their burrows. Quite likely this affords a degree of protection from various would-be predators. There may be a trade-off, too, if the frogs eat insects that might attack the spider's eggs.

Seasonal activity varies with climate. Where low temperature is not a factor, as in the tropics, rainfall is probably the chief determinant of the timing of the frogs' activity. Even in tropical rainforests there may be seasonal variation, and frogs may actively move about or call only during heavy rains. In tropical regions with a pronounced dry season, microhylids remain in burrows or other concealment and emerge only in the event of heavy rains. Few microhylid species live where freezing temperatures regularly occur, and those frogs depend on both warmth and rainfall to allow them to be active. Microhylids generally are nocturnal, but species at high elevations (and sometimes elsewhere) call in the daytime.

Feeding ecology and diet

Ants are a common prey of microhylid frogs, especially pointy-nosed species with a narrow gape. Just as in other features of their biological makeup, microhylids show diversity in diet. Even species that feed largely on ants do not ignore other tiny invertebrates. Larger species with a broad gape can eat bigger prey in addition to the usual insects; examples include lizards, frogs, and earthworms. Little is known of feeding behavior. Frogs found moving about on the forest floor may be foraging for food, but sit-and-wait behavior may be

more common. Free-swimming larvae of microhylids (as opposed to those that develop in confined situations and do not feed) all feed by filtering microscopic organisms from the water. Some with a funnel-shaped mouth specialize in taking food from the water's surface.

Reproductive biology

The common (and presumably primitive) mode of reproductive behavior in frogs includes courtship, in which male vocalization plays an important part, and amplexus accompanied by external fertilization of the eggs as they are extruded into water. The adults then go their separate ways. The tadpoles grow and metamorphose into frogs and then, according to the habit of the species, remain in the water or disperse to other habitats. Except for the fact that adults do not remain in the water, many microhylids engage in this sort of reproductive behavior. As is the case with other aspects of their biological makeup, microhylid breeding is not stereotyped.

Mating in most kinds of frogs requires amplexus, in which the male, situated dorsally, grasps the female just behind the front legs (axillary position) or just anterior to the hind legs (inguinal position), putting himself in position to fertilize the spawn as it is extruded (there are variations on these positions). Surprisingly little is recorded about mating in micro-hylids, but axillary amplexus is known in species that deposit eggs in water. In many, perhaps most, species of frogs, males that are ready to breed possess patches of cornified areas, sometimes literally spines, on one or more of the fingers. These areas enable the frog to maintain a grip on a slippery female while mating.

Such structures are absent in most microhylids, but they are found in at least two genera, Dyscophus and Hoplophryne. In the species of another genus, Anodonthyla, a single spine projects from the first finger. Gastrophryne and some other genera have another solution: ventral glands in the male secrete a substance that glues the pair together. The African genus Breviceps does this to bizarre effect. These are short-legged, rotund frogs, the female being much the larger of the two. Imagine a golf ball glued to a tennis ball. Very likely such adhesive behavior is more widespread in the Microhylidae than is recognized. Nothing at all is known about how the numerous direct-developing genyophrynine and aster-ophryine microhylids achieve insemination.

Breeding sites are diverse. Species with free-swimming but feeding larvae breed in quiet waters. According to the species, however, they may be permanent waters or sites that are dry but reliably fill in rainy seasons or fill only during sporadic heavy rains. Species with free-swimming but nonfeeding larvae breed in narrowly confined waters; examples include the leaf axils of bromeliads, tree holes, and pools in the crevices of logs. Species with direct embryonic development are divorced from free water and nest in burrows, leaf litter, and other sheltered terrestrial sites or in moisture-holding plants high in forest trees.

The timing of breeding is controlled primarily by the availability of adequately wet conditions and secondarily by temperature. In wet, largely tropical settings without distinct seasons, some individuals may be in a condition to breed year-round. Even here, however, there may be periodic variations in rainfall, which influence breeding activity. In drier tropical situations, breeding may be confined to discrete rainy seasons, and especially in temperate climate areas frogs may breed only at a warm, wet time of the year.

Vocalizing is one of the defining aspects of frogs, and microhylids are no exception. Probably all male microhylid frogs produce what are now called advertisement calls (formerly mating calls); even species that lack the secondary apparatus of a vocal sac with openings into the mouth cavity are known to call. Microhylid calls vary broadly, from pure-toned, high-pitched peeps to low, harsh notes, given either singly or in series. The characteristics of a call often define a species, but no correlation with higher systematic categories has been shown. Little research has been done on behavioral aspects of vocalization in microhylids. Certainly, the call serves to identify the caller to a female as an appropriate mate. In species of other families, a male's call has been shown to include aspects that may bear upon his suitability as a mate. Calling also functions in territoriality. This is to be expected, especially among forest-floor microhylids that do not migrate to water to breed.

Eliminating feeding is the first step beyond free-swimming larvae that feed themselves. In this mode, the eggs are heavily yolked, much larger than typical aquatic eggs, and are deposited in a small body of water, such as a tree hole or a leaf axil. The larva hatches (sometimes in an advanced stage of development) and subsists on the stored yolk until it metamorphoses. This mode of development evidently has evolved independently in different parts of the world, for example, in Madagascar (genera Anodonthyla, Platypelis, and Plethodontohyla), Southeast Asia (genus Kalophrynus), and South America (genus Syncope).

Direct development, where growth through metamorphosis occurs within the egg capsule, eliminates the necessity for depositing eggs in water but still requires a moist situation. Approximately one-half of all species of Microhylidae have this reproductive mode. All species of the subfamilies Aster-ophryinae and Genyophryninae evidently engage in this mode of development, as do some genera in other parts of the world, for example, the African rain frog of the genus Breviceps.

Direct development carries with it advantages as well as constraints. The need for a large amount of yolk greatly restricts the number of eggs a female frog can produce at one time. Thus, a high survival rate of eggs and hatchlings is essential if the species is to persist. Guarding of egg clutches by male frogs probably protects them from predaceous and parasitic insects and may minimize dehydration as well. Guarding behavior is known in eight genera of Asterophryinae and Genyophryninae and probably is universal in these families. Frogs of two genyophrynine genera, Aphantophryne and Liophryne, have even been seen to transport newly hatched young on their backs. In moist tropical regions, direct development greatly increases the potential area a species can inhabit, because mountainous areas generally are poor in still-water habitats of the sort many microhylids require for breeding. Also, such free water as exists is likely to be in rapidly flowing streams, and no microhylid tadpole is known to have the peculiar adaptations needed for life in such streams. As long as there is sufficient rainfall, however, frogs that undergo direct development can spread, breeding from underground to treetop habitats.

Conservation status

As of 2002, the IUCN classifies only two microhylids as Endangered: the Camiguin narrow-mouthed frog (Oreophryne nana), found only on one small island in the southern Philippines, and the black microhylid (Melanobatrachus indicus) of southwestern India. In addition, six species are classified as Vulnerable and three as Data Deficient. The Cape rain frog (Breviceps gibbosus) and the desert rain frog (Breviceps macrops), both with small ranges in South Africa, are listed as Vulnerable, as is the Negros truncate-toed chorus frog (Kaloula conjuncta negrosensis) of Negros Island in the Philippines and the tomato frog (Dyscophus antongilii) in Madagascar.

Most microhylids are small, dull-colored creatures that attract little attention and so are unlikely to become well enough known to be recognized as needing formal protection. Where they live in national parks, such as in northern Australia, protection of both habitats and individual species may be afforded, at least nominally. Many countries and lesser jurisdictions have laws to protect wildlife, frogs included, but too often these laws serve to inhibit scientific research without doing much else. Most microhylid frogs live in tropical rainforests, and such forests around the world are being destroyed at an alarming rate. It is inevitable that many species will become extinct before their plight is even recognized, and many others will disappear without achieving scientific recognition.

Significance to humans

Microhylids frogs figure in the diets of indigenous peoples in New Guinea, South America, and probably elsewhere. Given the small size of most species, the contribution of microhylids to human nutrition must be meager and the danger from overutilization slight.

Species accounts

List of Species

New Guinea bush frog

Asterophrys turpicola

subfamily

Asterophryinae

taxonomy

Ceratophrys turpicola Schlegel, 1837, Lobo district, Triton Bay, Dutch New Guinea (Irian Jaya, Indonesia).

other common names

None known.

physical characteristics

This species is the antithesis of the narrow-mouthed frog; its head (and, consequently, its gape) is as broad as its wide body. The eyelids bear fleshy spines, and the limbs and sides of the body are warty. It is one of the larger microhylids, reaching a body length of 2.5 in (65 mm). Its coloration is drab, with brown and black shades dominating.

distribution

This frog lives at low to moderate elevations in New Guinea, from the western end in Irian Jaya (Indonesia) to eastern Papua New Guinea.

habitat

This is a species of the forest floor, where it calls from sites below the surface. In at least one region in Papua New Guinea it has adapted to disturbed environments and is found in sub-urban gardens.

behavior

The New Guinea bush frog is noteworthy for its unusual defensive behavior. When annoyed, it may inflate the body and

hold the mouth open, exposing the bright blue tongue. If annoyance persists, the frog may leap at and bite its disturber, holding on for minutes. Curiously, closely similar behavior is found in unrelated but morphologically similar species of the genera Hemiphractus (Hylidae) and Ceratophrys (Leptodactylidae) in tropical America.

feeding ecology and diet

This species has a wide-ranging diet that includes lizards, insects, and frogs.

reproductive biology

Undoubtedly, the species has direct embryonic development, but no details of the reproductive habits are known.

conservation status

Not threatened.

significance to humans

None known.

Boulenger's callulops frog

Callulops robustus

subfamily

Asterophryinae

taxonomy

Mantophryne robusta Boulenger, 1898, Saint Aignan island, south of Fergusson island, British New Guinea (Misima Island, Louisiade Archipelago, Milne Bay Province, Papua New Guinea).

other common names

None known.

physical characteristics

This is a rather toadlike species, with a relatively broad head and body, large eyes, and short legs. At a maximum body length of almost 3 in (73 mm), it is one of the larger microhylids. Many individuals are dark purplish brown dorsally with a somewhat darker facial region. Small white spots may be present laterally on the body. A variant coloring is light reddish brown all over. These different colors may represent geographic variation.

distribution

Boulenger's callulops frog has a wide distribution in New Guinea, from the Birds Head peninsula at the western tip of the island to islands off the eastern end. It occurs from nearly sea level to an elevation of at least 4,800 ft (1,460 m).

habitat

The species lives in rainforest regions, though not necessarily primary forest.

behavior

The frogs are terrestrial, sheltering in burrows up to 3 ft (1 m) in length, which probably are appropriated by the frogs rather than constructed by them.

feeding ecology and diet

Nothing is recorded.

reproductive biology

Males call from the entrances to burrows, though they sometimes leave the burrows to call. A male frog was found sitting on a clutch of 17 eggs about 0.25 in (7 mm) in diameter in a decaying tree stump. The tails of the well-developed embryos were heavily vascularized and probably served for respiration, because the embryos had no gills.

conservation status

Not threatened.

significance to humans

None known.

Bushveld rain frog

Breviceps adspersus

subfamily

Brevicipitinae

taxonomy

Breviceps adspersus Peters, 1882, Damaraland (Namibia) and Transvaal (Republic of South Africa).

other common names

German: Gesprenkelter Kurzkopffrosch.

physical characteristics

This is a nearly globular frog with short legs and a blunt, pushedin snout. The toes are not webbed, and there are stout "spades" (inner and outer metatarsal tubercles) on the hind feet.

distribution

The species ranges across southern Africa, into Namibia, Botswana, Zimbabwe, Mozambique, and northern South Africa.

habitat

The frog inhabits open or savanna regions where the soil is sandy.

behavior

This is a burrowing frog that digs by using its "spades" while shuffling backward. Burrows may be as deep as 20 in (50 cm). For much of the year the frogs remain underground, living on stored fat, but they emerge to feed and call for mates in the wet summer. Such activity is mostly nocturnal but occasionally happens during the day.

feeding ecology and diet

Termites are the principal food, taken when they emerge by the thousands from their underground nests during rainy periods to mate and disperse.

reproductive biology

When the rains arrive, males call from the mouths of their burrows or sometimes while walking (not hopping) about. The mating posture is with the smaller male glued (literally) to the female's back. Thus positioned, the pair digs backward into the soil and hollows out a small cavity in which about 30 eggs are laid; the female may remain with the eggs. The young develop entirely within the egg capsule, hatching as tiny frogs about 0.25 in (6 mm) in length after four to six weeks.

conservation status

Not threatened. Two species of rain frogs with small ranges are considered Vulnerable, but the more widespread Bushveld rain frog apparently is more secure.

significance to humans

None known.

Boulenger's climbing frog

Anodonthyla boulengerii

subfamily

Cophylinae

taxonomy

Anodonthyla boulengerii Müller, 1892, Madagascar.

other common names

None known.

physical characteristics

This is a small frog, with a body length of 0.85 in (22 mm). The head is narrower than the body, and the snout is bluntly pointed. Teeth, which are lacking in most microhylids, are present in the upper jaw. The fingers and toes (except the first in each instance) have enlarged terminal disks; those of the fingers are much the broader. There is no webbing. The first finger of the male bears a sharp, projecting spine that may serve to help grip the female during amplexus. The background color is brown with varying paler or darker brown markings.

distribution

The species ranges across eastern Madagascar.

habitat

This is an arboreal species, but sometimes it is found under the forest floor litter.

behavior

Little is known aside from reproductive behavior.

feeding ecology and diet

Like so many other microhylids, this species feeds on ants.

reproductive biology

Males are reported to call from the trunks of trees and ferns as well as other vegetation but rarely from leaves. This is one of many species of microhylids whose breeding habits diverge from those more typical of frogs. The 25–30 eggs are small (less than 0.1 in, or 2 mm) and are laid in water held in tree cavities or leaf axils. The male remains with the eggs as they develop and through the period of larval growth, which lasts less than a month. The tadpoles take no food; they survive and grow through metamorphosis on energy supplied by the yolk.

conservation status

Not threatened.

significance to humans

None known.

Fry's whistling frog

Austrochaperina fryi

subfamily

Genyophryninae

taxonomy

Austrochaperina brevipes Fry, 1915, Bloomfield River, near Cooktown, northeastern Queensland, Australia.

other common names

None known.

physical characteristics

This is a small frog—females attain a body length of 1.3 in (35 mm), and males are slightly smaller. The species has average frog morphologic features: rather than the fat body, narrow head, small eyes, and pointed snout of the classic microhylid, the slightly rotund body is only a little wider than the head, the eyes are relatively large, and the snout is rounded. The toes are not webbed, and the tips of the fingers and toes are slightly broadened. The body is brown above, with a reddish tint, and the facial region is black.

Species of microhylid frogs often are confusingly similar in morphologic characteristics. In this instance, Austrochaperina fryi cannot be distinguished reliably by morphologic features from another Australian species, Austrochaperina robusta, but the two have distinctly different calls: A. fryi gives a series of brief whistles, whereas A. robusta produces whistles in couplets.

distribution

The species occurs in northeast Queensland, Australia.

habitat

The habitat is the leaf litter on the floor of rainforest, where the frogs hide by day amid the leaves or under other cover. The range in elevation is from virtually sea level to 3,600 ft (1,100 m).

behavior

Little is known aside from reproductive behavior.

feeding ecology and diet

Nothing is recorded, but the frogs undoubtedly eat small invertebrates.

reproductive biology

At night males call from superficial cover on the forest floor, not from deep within the leaf litter. Like other members of the subfamily, A. fryi has direct embryonic development. Large eggs, about 0.2 in (5 mm) in diameter, are deposited in sheltered tered sites on the forest floor and are attended by the male. The clutch size is seven to 12 eggs. Hatchling frogs are about 0.25 in (6 mm) in body length.

conservation status

Not threatened. The presence of this species in protected areas may ensure its survival, though forest destruction may fragment the range.

significance to humans

None known.

Wilhelm rainforest frog

Cophixalus riparius

subfamily

Genyophryninae

taxonomy

Cophixalus riparius Zweifel, 1962, at an elevation of 9,100 ft (2,774 m) beside Pengagl Creek on the eastern slope of Mount Wilhelm, Territory of New Guinea (Simbu Province, Papua New Guinea).

other common names

None known.

physical characteristics

The largest species of its genus, the Wilhelm rainforest frog reaches a body length of 2 in (50 mm). The habit is that of a treefrog: large hands, fingers and toes with broad terminal disks, and large eyes. The background color is tan, with varying darker brown markings and sometimes a purple tinge.

distribution

The species lives in the central ranges of Papua New Guinea at elevations of about 6,000–9,000 ft (1,900–2,800 m).

habitat

This species inhabits rainforest.

behavior

The Wilhelm rainforest frog is an adaptable, scansorial (climbing) frog that is at home high in forest trees or on steep surfaces at ground level. It is found in pandanus trees and in cavities in epiphytic plants (ones that grow attached to trees) as well as in holes on steep banks, such as road cuts.

feeding ecology and diet

Nothing is recorded.

reproductive biology

Like other genyophrynine microhylids, the Wilhelm rainforest frog has direct embryonic development. In one instance, a string of 27 eggs, about 0.2 in (6 mm) in diameter and joined by short cords, was found in a burrow in a soil bank with an attending frog. Male frogs call from such burrows. Eggs also are deposited in sheltered arboreal situations, where frogs can be heard calling from far out of reach.

conservation status

Not threatened.

significance to humans

None known.

Horned land frog

Sphenophryne cornuta

subfamily

Genyophryninae

taxonomy

Sphenophryne cornuta Peters and Doria, 1878, near the Wa Samson river in northern New Guinea (Irian Jaya, Indonesia).

other common names

None known.

physical characteristics

The maximum body length is about 1.6 in (41 mm); females are slightly larger than males. The body is relatively slender, with long legs and a somewhat pointed snout. Enlarged terminal disks on the fingers and toes, both of which are not webbed, give the species the aspect of a tree frog, and a pointed tubercle on each eyelid distinguishes it from other species with which it might be confused. The color varies from dark to light brown above and gray laterally, with largely gray, orange, or red undersides.

distribution

The species inhabits most of New Guinea at low to moderate elevations, usually below 4,100 ft (1,250 m).

habitat

This species inhabits rainforest.

behavior

Males call at night from shrubs or other low vegetation but apparently not from high in trees. Females may be more terrestrial (when they are not attracted to calling males), but this is not known. Calls that differ from the presumed advertisement call have been heard in a call-response sequence between two individuals, suggesting a territorial function.

feeding ecology and diet

Food habits have not been studied, but small invertebrates must be the mainstay.

reproductive biology

The presumed advertisement call is a rattling sound lasting up to three seconds. The presence of large, heavily yolked eggs in females essentially confirms that this species, like other microhylids in New Guinea, has direct embryonic development, but this remains to be verified by the discovery of eggs and an associated parent.

conservation status

Not threatened. As a widely distributed species, the horned land frog is less likely than many others to be exterminated by destruction of rainforest.

significance to humans

None known.

Saffron-bellied frog

Chaperina fusca

subfamily

Microhylinae

taxonomy

Chaperina fusca Mocquard, 1893, Sintang, Borneo (Kalimantan, Indonesia).

other common names

None known.

physical characteristics

Males grow only up to 0.8 in (21 mm) and females to 0.9 in (24 mm) in body length. The body is slender to moderately stocky; the head is as wide as, or slightly narrower, than the body; and the snout is rounded. The tips of the fingers bear expanded terminal disks, and the toes have disks of similar size; the toes have scant webbing. Each elbow and heel has a conical dermal projection. For a microhylid, this is a colorful frog. All undersurfaces have large yellow spots against a network of black, and this pattern extends well up onto the sides of the body. The dorsal surfaces of the head and body are black, with a pattern of greenish yellow to silvery flecks.

distribution

The range includes the Malay Peninsula and Borneo northward to the southern Philippine islands of Jolo, Mindanao, and Palawan.

habitat

The saffron-bellied frog inhabits primarily the ground surface layer of forest. It is found both in level, lowland country and in hills up to 5,900 ft (1,800 m).

behavior

When not breeding, these frogs hide under litter, such as fallen leaves, during the day and may climb into low vegetation at night.

feeding ecology and diet

The diet is not described, but the food undoubtedly is small invertebrates.

reproductive biology

Males call in chorus by day around small, temporary pools, where the eggs are laid and the tadpoles develop.

conservation status

Not threatened.

significance to humans

None known.

Eastern narrow-mouthed toad

Gastrophryne carolinensis

subfamily

Microhylinae

taxonomy

Engystoma carolinense Holbrook, 1836, Charleston, South Carolina, and extending westward to the lower Mississippi River, United States.

other common names

German: Carolina-Engmaulfrosch; Spanish: Ranita olivo.

physical characteristics

This small frog grows up to 1.5 in (3.8 cm) in length. It has a chunky body tapering to a narrow head, with a fold of skin across the head behind the small eyes and a somewhat pointed snout. The toes lack webbing. The dorsum varies in color, generally a shade of brown more or less distinct from a paler shade laterally.

distribution

The eastern narrow-mouthed toad occurs in the southern and eastern United States from eastern Texas and Oklahoma to Maryland and south to the Gulf of Mexico and the tip of Florida. It has been introduced into two islands in the Bahamas. A close relative, the Great Plains narrow-mouthed toad (Gastrophryne olivacea), has a complementary distribution westward to southern New Mexico and southern Arizona and south on both coasts of Mexico.

habitat

The species inhabits mostly coastal plain and piedmont terrain and, rarely, mountains; it ranges from seashore to forest, generally avoiding dryer conditions.

behavior

This secretive, terrestrial species seldom is seen except in breeding choruses, unless one turns over rocks, logs, or other ground surface cover, when it is quick to escape. Activity is almost wholly nocturnal. Distasteful and possibly toxic skin secretions provide some protection from enemies, but egrets, bullfrogs (Rana catesbeiana), and garter snakes (species of Thamnophis) are known predators. The secretions help protect the frogs from attack by ants.

feeding ecology and diet

This species preys on a wide variety of small invertebrates up to about 0.25 in (6 mm) in length; ants, beetles, and termites constitute the bulk of the diet.

reproductive biology

Breeding takes place during heavy rains that fill or supplement permanent or semipermanent pools. The breeding season may be from April to October in the south, but it takes place over a narrower span farther north. Males call in the water or from sheltered sites nearby. They grip females in axillary amplexus while becoming glued to them by secretions from ventral skin glands. The call, which lasts up to four seconds, is often compared to the bleat of a lamb. On average, about 500 eggs are deposited as a surface film, not necessarily in one continuous batch. The duration of larval development ranges from 20 to 67 days, with the longer periods in the northern part of the range. Newly metamorphosed frogs are less than 0.5 in (11 mm) in length.

conservation status

Not threatened.

significance to humans

None known.

Bolivian bleating frog

Hamptophryne boliviana

subfamily

Microhylinae

taxonomy

Chiasmocleis boliviana Parker, 1927, Buena Vista, Santa Cruz, Bolivia.

other common names

None known.

physical characteristics

This frog, the only species of its genus, has the classic microhylid habitus of squat body tapering to a narrow head with small eyes and a pointed snout. Females reach a body length of 1.75 in (44 mm), and males are slightly smaller. The toes have no webbing, and the tips of the fingers and toes are slightly expanded. The flanks and sides of the head are dark brown, sharply set off from the tan to reddish dorsal coloring.

distribution

The species ranges across South America and is distributed widely on the western and northern sides of the Amazon basin in Bolivia, Peru, Ecuador, French Guiana, Surinam, and Brazil.

habitat

The frog inhabits mature and secondary forests at moderately low elevations (700–1,100 ft, or 220–340 m).

behavior

Little is known of the activities of these frogs, apart from when they are breeding. They have been found feeding at columns of ants on the forest floor at night and as high as 5 ft (1.5 m) up on the trunks and branches of trees.

feeding ecology and diet

Ants make up the bulk of the diet.

reproductive biology

Following the first heavy rainfall at the onset of the rainy season, frogs congregate in great numbers for a few days at lotic waters then formed or augmented. Males begin calling in daylight as they approach the ponds and then from the water, where mating and depositing of eggs take place. Eggs are deposited in clutches about 4 in (10 cm) in diameter, with about 200 eggs in each clutch. Presumably, one female lays several clutches, as one frog was found to contain more than 2,000 mature eggs. The tadpoles hatch after about a day and a half, but the period of growth to metamorphosis has not been measured. Tadpoles are preyed upon by a variety of animals, including dragonfly larvae and freshwater crabs. The frogs leave the ponds right after breeding, but later intense rain following a dry period may initiate another short period of reproductive activity.

conservation status

Not threatened.

significance to humans

None known.

Malaysian painted frog

Kaloula pulchra

subfamily

Microhylinae

taxonomy

Kaloula pulchra Gray, 1831, China.

other common names

German: Indischer Ochsenfrosch; Spanish: Microhilido asiático.

physical characteristics

This species is rather large for a microhylid, up to 3 in (75 mm) long. The body is rotund, with a blunt, rounded snout; the legs are short and stout. The hind feet have a projecting "spade" on the sole just anterior to the heel; the toes are only slightly webbed.

distribution

The native range is from southern China through Indochina to Sumatra. The species' presence in Borneo and Sulawesi is thought to be due to introductions, probably inadvertent. Kaloula taprobanica, once considered to be a subspecies of K. pulchra, ranges from northeastern India to Sri Lanka, so frogs of this sort are widespread.

habitat

The Malaysian painted frog is unusual, in that it is abundant in human settlements but is not found in undisturbed habitats.

The frogs take shelter in burrows, rubbish heaps, and the like. This association with people may explain spotty occurrences out of the apparent natural range.

behavior

This is a secretive, terrestrial frog that utilizes the spadelike structures (metatarsal tubercles) on its hind feet to burrow backward into the soil. It is most likely to be seen when congregating to breed.

feeding ecology and diet

Ants constitute most of the diet, along with other small insects.

reproductive biology

Breeding takes place only when heavy rains fill ditches and other temporary sources of water. There the males float high in the water, giving loud, honking calls. Their rounded shape is exaggerated even more when they inflate while floating and calling. In such ephemeral habitats, larval growth typically is rapid, but it may not be fast enough to reach completion before the water dries up.

conservation status

Not threatened.

significance to humans

None known.

Ornate narrow-mouthed frog

Microhyla ornata

subfamily

Microhylinae

taxonomy

Engystoma ornatum Duméril and Bibron, 1841, Malabar coast, India.

other common names

None known.

physical characteristics

This is a small frog: males grow to about 0.8 in (23 mm) and females to 1 in (25 mm) in body length. The rather rotund body tapers to a narrow head and bluntly pointed snout. Finger and toe tips are pointed, and the toes have only scant webbing. The dorsal ground color is light olive brown and sometimes grayish or reddish. A prominent dorsal pattern includes black bands that originate behind the head and diverge as they pass posteriorly.

distribution

This is a widely distributed species that ranges from eastern and southern China, including Hainan, to Taiwan and the Ryukyu Islands; west to Pakistan, Nepal, India, and Sri Lanka; and south through Indochina and the Malay Peninsula.

habitat

Typical habitats are grassy areas near flooded rice paddies, ditches, and pools up to the lower slopes of mountains at about 3,000 ft (900 m). The association with rice paddies and similar agricultural sites may help explain this species' wide geographic distribution.

behavior

The frogs are nocturnal, taking daytime shelter in grass or the crevices in drying soil or under surface litter. They are said to be poor swimmers but very active jumpers.

feeding ecology and diet

The diet is not described, but undoubtedly small invertebrates are taken.

reproductive biology

Breeding takes place after heavy rain, when males call from the water in flooded rice fields and similar habitats. The female deposits several hundred eggs that float in a film at the surface of the water, and the tadpoles exhibit unusually rapid growth. This, no doubt, is associated with the ephemeral nature of the water in many breeding sites. Tadpoles are largely transparent, which makes them inconspicuous in shallow water.

conservation status

Not threatened.

significance to humans

None known.

Timbo disc frog

Synapturanus salseri

subfamily

Microhylinae

taxonomy

Synapturanus salseri Pyburn, 1975, Timbó, Vaupés, Colombia.

other common names

None known.

physical characteristics

This is a small (1.1 in, or 28 mm) frog with a stout body that tapers to a narrow head with a blunt, overhanging snout. There is a transverse fold of skin just behind the small eyes, and the tympanum is concealed completely. The toes are not webbed, and the inner metatarsal tubercle is indistinct, not enlarged into a digging spade. The dorsum is gray-brown with small spots over the body and legs varying from cream to orange.

distribution

The species is known only from southeastern Colombia and adjacent Ecuador and Venezuela. The range of the genus (three species) extends to eastern Brazil.

habitat

The species lives on the floor of rainforest.

behavior

These are secretive frogs that live in burrows beneath the forest floor under layers of fallen leaves and root tangles; they emerge rarely, if ever, into the open.

feeding ecology and diet

These frogs are known to eat ants and spiders.

reproductive biology

The call, a brief whistle, is given only during heavy rainfall, presumably from the mouth of the burrow. Reproduction is entirely terrestrial. The eggs are large and few (four to six) and are deposited in the burrow and accompanied by the male frog. The hatched tadpoles do not feed but live instead on the stored yolk until they metamorphose.

conservation status

Not threatened.

significance to humans

None known.

Pyburn's pancake frog

Otophryne pyburni

subfamily

Otophryninae

taxonomy

Otophryne pyburni Campbell and Clarke, 1998, Wacará, Vaupés, Colombia.

other common names

None known.

physical characteristics

Females grow up to 2.2 in (56 mm) in length, and males are slightly smaller. The body is rather broad, with short legs, and tapers to a sharp-pointed, projecting snout. The tympanum is distinct and slightly greater in diameter than the eye. The dorsal surfaces are reddish brown to grayish yellow, uniform or with darker markings, including a mid-dorsal stripe, and separated by a pale stripe from the darker side of the body. The general impression is that of a dead leaf.

distribution

The frog is found in South America. The range is from southeastern Colombia eastward through southern Venezuela and Guyana to French Guiana.

habitat

This species lives on the forest floor in sandy soils of the rainforest.

behavior

Individuals probably stay underground much of the time.

feeding ecology and diet

Another species of Otophryne is known to feed on ants, and it is likely that Pyburn's pancake frog does also.

reproductive biology

Males call during the day from sheltered sites, such as beneath leaf litter or under root tangles beside streams. The unpigmented eggs are large (0.2 in, or 5 mm) in diameter and probably are deposited in a nest cavity near a stream, as is known for another species of Otophryne. The tadpole has characters unique within the Microhylidae. It possesses a row of sharp, keratinized teeth in the upper and lower jaws, and the spiracle, instead of opening mid-ventrally, is on the lower-left side of the body near the base of the tail. As the tadpole grows, the spiracle extends as a tube that may reach halfway along the tail. Probably the larvae of the other two species of Otophryne are similar. The function of the teeth is uncertain. One suggestion is that the tadpoles are predaceous. Another, perhaps more plausible, idea is that the teeth serve to screen out sand grains as the larva filter-feeds in shallow water. Tadpoles of Pyburn's pancake frog have been found hiding under leaves in tiny, shallow streams.

conservation status

Not threatened.

significance to humans

None known.

Banded rubber frog

Phrynomantis bifasciatus

subfamily

Phrynomerinae

taxonomy

Brachymerus bifasciatus Smith, 1847, country to the east and northeast of the Cape Colony, Republic of South Africa.

other common names

English: Red-banded frog; German: Wendehalsfrosch.

physical characteristics

The banded rubber frog is of medium size, with a body length up to about 2.75 in (68 mm). This is a strikingly colored frog; the dorsum is black with red bands running from the snout over the eyelids to the rear of the body and red spotting on the limbs. The body is moderately robust, with the tips of the fingers expanded into truncate disks; the legs are short, and the toes have no webbing. The skin is smooth and shiny; its texture is responsible for the name rubber frog.

distribution

The frog is found in Africa, from Somalia and Zaire to South Africa.

habitat

This species inhabits open or savanna country.

behavior

These frogs are nocturnal and spend the dry season underground in holes or termitaria. They tend to walk or run rather than hop, and they burrow backward, though they are not equipped with the large "spades" on the hind feet that are found in some other microhylids. Secretions from glands in the skin have been known to cause skin irritations in people.

feeding ecology and diet

Ants and termites are the principal food.

reproductive biology

Reproduction takes place in rain pools and similar inundated sites. Males give their melodious trill from beside or in shallow water; when they mate, they hold the female in axillary amplexus. Masses of as many as 1,500 eggs are attached to submerged weeds. Development to metamorphosis at a body length of about 0.5 in (13 mm) takes about one month. The tadpole has a whiplike tail tip, which it vibrates while it hangs suspended at a steep angle in the water filtering its microscopic food. As in other midwater tadpoles (as opposed to bottom feeders), these larvae have their eyes at the sides of the head, which permits a broad range of vision both above and below.

conservation status

Not threatened.

significance to humans

None known.

Resources

Books

Parker, H. W. A Monograph of the Frogs of the Family Microhylidae. London: British Museum, 1934.

Periodicals

Blum, J. P, and J. I. Menzies. "Notes on Xenobatrachus and Xenorhina (Amphibia: Microhylidae) from New Guinea with Description of Nine New Species." Alytes 7, no. 4 (1988): 125–163.

Burton, T. C. "A Reassessment of the Papuan Subfamily Asterophryinae (Anura: Microhylidae)." Records of the South Australian Museum 19, no. 10 (1986): 405–450.

Carvalho, Antenor Leitão de. "A Preliminary Synopsis of the Genera of American Microhylid Frogs." Occ. Pap. Mus. Zool. Univ. Michigan 555 (1954): 1–19.

Donnelly, Maureen, Rafael O. de Sá, and C. Guyer. "Description of the Tadpoles of Gastrophryne pictiventris and Nelsonophryne aterrima (Anura: Microhylidae), with a Review of Morphological Variation in Free-swimming Microhylid Larvae." American Museum Novitates 2976 (1990): 1–19.

Menzies, James I. "A Study of Albericus (Anura: Microhylidae) of New Guinea." Australian Journal of Zoology 47 (1999): 327–360.

Wild, Erik Russell. "New Genus and Species of Amazonian Microhylid Frog with a Phylogenetic Analysis of New World Genera." Copeia 1995, no. 4 (1995): 837–849.

Zweifel, Richard G. "A New Genus and Species of Microhylid Frog from the Cerro de la Neblina Region of Venezuela and a Discussion of Relationships among New World Microhylid Genera." American Museum Novitates 2863 (1986): 1–24.

——. "Australian Frogs of the Family Microhylidae." Bulletin of the American Museum of Natural History 182, no. 3 (1985): 265–388.

——. "Partition of the Australopapuan Microhylid Frog Genus Sphenophryne with Descriptions of New Species." Bulletin of the American Museum of Natural History 253 (2000): 1–130.

——. "Results of the Archbold Expeditions. No. 97. A Revision of the Frogs of the Subfamily Asterophryinae Family Microhylidae." Bulletin of the American Museum of Natural History 148, no. 3 (1972): 411–546.

Richard G. Zweifel, PhD