The Variety of Amphibian Reproduction

Highlights

Amphibian Reproduction
Become a Member Already a member? Indonesia is the world's largest exporter of frog meat, exporting more than 5, tonnes of frog meat each year, mostly to France, Belgium and Luxembourg. The ostial opening is very elastic and does not respond to the respiratory or heart activity, as some have described. In a few cases, captive breeding programs have been established and have largely been successful. Some frog calls are so loud that they can be heard up to a mile away. Archaeobatrachia , which includes four families of primitive frogs; Mesobatrachia , which includes five families of more evolutionary intermediate frogs; and Neobatrachia , by far the largest group, which contains the remaining 24 families of modern frogs, including most common species throughout the world. The identifying features which distinguish it from the female are a darkened thumb pad which changes thickness and color intensity as the breeding season approaches; a distinct low, guttural croaking sound with the accompanying swelling by air of the lateral vocal sacs located between the tympanum and the forearm; a more slender and streamlined body than that of the female; and the absence of coelomic cilia except in the peritoneal funnels on the ventral face of the kidneys.

Salamanders and Newts

How Do Amphibians Reproduce?

Want to watch this again later? Amphibians are organisms that spend part of their lives developing in water before they're able to live on both land and in water. This unique ecological characteristic means they have a different reproductive strategy than humans.

What Is an Amphibian? Salamanders and Newts Salamanders and newts usually reproduce during the winter months. Longtailed Salamander Toads Males call out to females by croaking, so every time you hear a toad or frog calling, you are really hearing them signal to potential mates that they are ready to reproduce!

In the amplexus position, the male grasps on to the female from behind. Frogs Frogs reproduce very similar to toads. Frog eggs are laid in water in high numbers.

Try it risk-free No obligation, cancel anytime. Want to learn more? Select a subject to preview related courses: Caecilians Caecilians are sometimes called blindworms; they are a legless amphibian that resembles a worm. Caecilians look a bit like worms. Lesson Summary We've learned that there are four groups of amphibians - toads, frogs, salamanders and newts, and caecilians, and each of them uses a slightly different method to reproduce.

Salamanders and newts use a spermatophore so that eggs can be fertilized internally without sexual intercourse. Toads and frogs use the amplexus position to signal the male and female to simultaneously release eggs and sperm so external fertilization can take place. Caecilians use internal fertilization and often give live birth.

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Password Confirm Password confirm is required. The illium has elongated and formed a mobile joint with the sacrum which, in specialist jumpers such as ranids and hylids, functions as an additional limb joint to further power the leaps. The tail vertebrae have fused into a urostyle which is retracted inside the pelvis. This enables the force to be transferred from the legs to the body during a leap. The muscular system has been similarly modified.

The hind limbs of ancestral frogs presumably contained pairs of muscles which would act in opposition one muscle to flex the knee, a different muscle to extend it , as is seen in most other limbed animals.

However, in modern frogs, almost all muscles have been modified to contribute to the action of jumping, with only a few small muscles remaining to bring the limb back to the starting position and maintain posture. Many frogs have webbed feet and the degree of webbing is directly proportional to the amount of time the species spends in the water. Arboreal frogs have pads located on the ends of their toes to help grip vertical surfaces. These are not suction pads, the surface consisting instead of columnar cells with flat tops with small gaps between them lubricated by mucous glands.

When the frog applies pressure, the cells adhere to irregularities on the surface and the grip is maintained through surface tension. This allows the frog to climb on smooth surfaces, but the system does not function efficiently when the pads are excessively wet.

In many arboreal frogs, a small "intercalary structure" on each toe increases the surface area touching the substrate. Furthermore, since hopping through trees can be dangerous, many arboreal frogs have hip joints to allow both hopping and walking. Some frogs that live high in trees even possess an elaborate degree of webbing between their toes. This allows the frogs to "parachute" or make a controlled glide from one position in the canopy to another. Ground-dwelling frogs generally lack the adaptations of aquatic and arboreal frogs.

Most have smaller toe pads, if any, and little webbing. Some burrowing frogs such as Couch's spadefoot Scaphiopus couchii have a flap-like toe extension on the hind feet, a keratinised tubercle often referred to as a spade, that helps them to burrow. Sometimes during the tadpole stage, one of the developing rear legs is eaten by a predator such as a dragonfly nymph.

In some cases, the full leg still grows, but in others it does not, although the frog may still live out its normal lifespan with only three limbs. Occasionally, a parasitic flatworm Ribeiroia ondatrae digs into the rear of a tadpole, causing a rearrangement of the limb bud cells and the frog develops an extra leg or two.

A frog's skin is protective, has a respiratory function, can absorb water and helps control body temperature. It has many glands, particularly on the head and back, which often exude distasteful and toxic substances granular glands. The secretion is often sticky and helps keep the skin moist, protects against the entry of moulds and bacteria, and make the animal slippery and more able to escape from predators. It usually splits down the middle of the back and across the belly, and the frog pulls its arms and legs free.

The sloughed skin is then worked towards the head where it is quickly eaten. Being cold-blooded, frogs have to adopt suitable behaviour patterns to regulate their temperature. To warm up, they can move into the sun or onto a warm surface; if they overheat, they can move into the shade or adopt a stance that exposes the minimum area of skin to the air.

This posture is also used to prevent water loss and involves the frog squatting close to the substrate with its hands and feet tucked under its chin and body. In cool damp conditions, the colour will be darker than on a hot dry day. The grey foam-nest tree frog Chiromantis xerampelina is even able to turn white to minimize the chance of overheating. Many frogs are able to absorb water and oxygen directly through the skin, especially around the pelvic area, but the permeability of a frog's skin can also result in water loss.

Glands located all over the body exude mucus which helps keep the skin moist and reduces evaporation. Some glands on the hands and chest of males are specialized to produce sticky secretions to aid in amplexus.

Similar glands in tree frogs produce a glue-like substance on the adhesive discs of the feet. Some arboreal frogs reduce water loss by having a waterproof layer of skin, and several South American species coat their skin with a waxy secretion. Other frogs have adopted behaviours to conserve water, including becoming nocturnal and resting in a water-conserving position. Some frogs may also rest in large groups with each frog pressed against its neighbours.

This reduces the amount of skin exposed to the air or a dry surface, and thus reduces water loss. They contain blood vessels and are thought to increase the area of the skin available for respiration. Some species have bony plates embedded in their skin, a trait that appears to have evolved independently several times. Camouflage is a common defensive mechanism in frogs.

Most camouflaged frogs are nocturnal; during the day, they seek out a position where they can blend into the background and remain undetected.

Some frogs have the ability to change colour , but this is usually restricted to a small range of colours. For example, White's tree frog Litoria caerulea varies between pale green and dull brown according to the temperature, and the Pacific tree frog Pseudacris regilla has green and brown morphs, plain or spotted, and changes colour depending on the time of year and general background colour. Certain frogs change colour between night and day, as light and moisture stimulate the pigment cells and cause them to expand or contract.

The skin of a frog is permeable to oxygen and carbon dioxide , as well as to water. There are blood vessels near the surface of the skin and when a frog is underwater, oxygen diffuses directly into the blood. When not submerged, a frog breathes by a process known as buccal pumping. Its lungs are similar to those of humans, but the chest muscles are not involved in respiration, and no ribs or diaphragm exist to help move air in and out. Instead, it puffs out its throat and draws air in through the nostrils, which in many species can then be closed by valves.

When the floor of the mouth is compressed, air is forced into the lungs. Frogs have three-chambered hearts , a feature they share with lizards. When these chambers contract, the two blood streams pass into a common ventricle before being pumped via a spiral valve to the appropriate vessel, the aorta for oxygenated blood and pulmonary artery for deoxygenated blood. The ventricle is partially divided into narrow cavities which minimizes the mixing of the two types of blood.

These features enable frogs to have a higher metabolic rate and be more active than would otherwise be possible. Some species of frog have adaptations that allow them to survive in oxygen deficient water.

The Titicaca water frog Telmatobius culeus is one such species and has wrinkly skin that increases its surface area to enhance gas exchange. It normally makes no use of its rudimentary lungs but will sometimes raise and lower its body rhythmically while on the lake bed to increase the flow of water around it.

Frogs have maxillary teeth along their upper jaw which are used to hold food before it is swallowed. These teeth are very weak, and cannot be used to chew or catch and harm agile prey. Instead, the frog uses its sticky, cleft tongue to catch flies and other small moving prey. The tongue normally lies coiled in the mouth, free at the back and attached to the mandible at the front.

It can be shot out and retracted at great speed. It then proceeds to the small intestine duodenum and ileum where most digestion occurs. Pancreatic juice from the pancreas, and bile, produced by the liver and stored in the gallbladder, are secreted into the small intestine, where the fluids digest the food and the nutrients are absorbed. The food residue passes into the large intestine where excess water is removed and the wastes are passed out through the cloaca.

Although adapted to terrestrial life, frogs resemble freshwater fish in their inability to conserve body water effectively. When they are on land, much water is lost by evaporation from the skin.

The excretory system is similar to that of mammals and there are two kidneys that remove nitrogenous products from the blood. Frogs produce large quantities of dilute urine in order to flush out toxic products from the kidney tubules. A few species of tree frog with little access to water excrete the even less toxic uric acid. All bodily wastes exit the body through the cloaca which terminates in a cloacal vent. In the male frog, the two testes are attached to the kidneys and semen passes into the kidneys through fine tubes called efferent ducts.

It then travels on through the ureters, which are consequently known as urinogenital ducts. There is no penis, and sperm is ejected from the cloaca directly onto the eggs as the female lays them. The ovaries of the female frog are beside the kidneys and the eggs pass down a pair of oviducts and through the cloaca to the exterior. When frogs mate, the male climbs on the back of the female and wraps his fore limbs round her body, either behind the front legs or just in front of the hind legs.

This position is called amplexus and may be held for several days. These include the development of special pads on his thumbs in the breeding season, to give him a firm hold. Males have vocal cords and make a range of croaks, particularly in the breeding season, and in some species they also have vocal sacs to amplify the sound. Frogs have a highly developed nervous system that consists of a brain, spinal cord and nerves.

Many parts of frog brains correspond with those of humans. It consists of two olfactory lobes, two cerebral hemispheres, a pineal body, two optic lobes, a cerebellum and a medulla oblongata. Muscular coordination and posture are controlled by the cerebellum , and the medulla oblongata regulates respiration, digestion and other automatic functions.

Frogs have ten pairs of cranial nerves which pass information from the outside directly to the brain, and ten pairs of spinal nerves which pass information from the extremities to the brain through the spinal cord. The eyes of most frogs are located on either side of the head near the top and project outwards as hemispherical bulges. Each eye has closable upper and lower lids and a nictitating membrane which provides further protection, especially when the frog is swimming.

The common toad Bufo bufo has golden irises and horizontal slit-like pupils, the red-eyed tree frog Agalychnis callidryas has vertical slit pupils, the poison dart frog has dark irises, the fire-bellied toad Bombina spp. The irises of the southern toad Anaxyrus terrestris are patterned so as to blend in with the surrounding camouflaged skin.

The distant vision of a frog is better than its near vision. Calling frogs will quickly become silent when they see an intruder or even a moving shadow but the closer an object is, the less well it is seen.

Frogs can hear both in the air and below water. They do not have external ears ; the eardrums tympanic membranes are directly exposed or may be covered by a layer of skin and are visible as a circular area just behind the eye.

The size and distance apart of the eardrums is related to the frequency and wavelength at which the frog calls. In some species such as the bullfrog, the size of the tympanum indicates the sex of the frog; males have tympani that are larger than their eyes while in females, the eyes and tympani are much the same size. The middle ear contains semicircular canals which help control balance and orientation. In the inner ear, the auditory hair cells are arranged in two areas of the cochlea, the basilar papilla and the amphibian papilla.

The former detects high frequencies and the latter low frequencies. In some species that inhabit arid regions, the sound of thunder or heavy rain may arouse them from a dormant state.

The call or croak of a frog is unique to its species. Frogs create this sound by passing air through the larynx in the throat. In most calling frogs, the sound is amplified by one or more vocal sacs, membranes of skin under the throat or on the corner of the mouth, that distend during the amplification of the call.

Some frog calls are so loud that they can be heard up to a mile away. Frogs in the genera Heleioporus and Neobatrachus lack vocal sacs but can still produce a loud call. Their buccal cavity is enlarged and dome-shaped, acting as a resonance chamber that amplifies the sound.

Species of frog that lack vocal sacs and that do not have a loud call tend to inhabit areas close to constantly noisy, flowing water. They need to use an alternative means to communicate. The coastal tailed frog Ascaphus truei lives in mountain streams in North America and does not vocalize. The main reason for calling is to allow male frogs to attract a mate. Males may call individually or there may be a chorus of sound where numerous males have converged on breeding sites.

Females of many frog species, such as the common tree frog Polypedates leucomystax , reply to the male calls, which acts to reinforce reproductive activity in a breeding colony. The rationale for this is thought to be that by demonstrating his prowess, the male shows his fitness to produce superior offspring. A different call is emitted by a male frog or unreceptive female when mounted by another male.

This is a distinct chirruping sound and is accompanied by a vibration of the body. All of these calls are emitted with the mouth of the frog closed. It is typically used when the frog has been grabbed by a predator and may serve to distract or disorientate the attacker so that it releases the frog. Many species of frog have deep calls. The croak of the American bullfrog Rana catesbiana is sometimes written as "jug o' rum".

During extreme conditions, some frogs enter a state of torpor and remain inactive for months. In colder regions, many species of frog hibernate in winter. Those that live on land such as the American toad Bufo americanus dig a burrow and make a hibernaculum in which to lie dormant. Others, less proficient at digging, find a crevice or bury themselves in dead leaves.

Aquatic species such as the American bullfrog Rana catesbeiana normally sink to the bottom of the pond where they lie, semi-immersed in mud but still able to access the oxygen dissolved in the water.

Their metabolism slows down and they live on their energy reserves. Some frogs can even survive being frozen. Ice crystals form under the skin and in the body cavity but the essential organs are protected from freezing by a high concentration of glucose.

An apparently lifeless, frozen frog can resume respiration and the heart beat can restart when conditions warm up. At the other extreme, the striped burrowing frog Cyclorana alboguttata regularly aestivates during the hot, dry season in Australia, surviving in a dormant state without access to food and water for nine or ten months of the year.

It burrows underground and curls up inside a protective cocoon formed by its shed skin. Researchers at the University of Queensland have found that during aestivation, the metabolism of the frog is altered and the operational efficiency of the mitochondria is increased.

This means that the limited amount of energy available to the comatose frog is used in a more efficient manner. This survival mechanism is only useful to animals that remain completely unconscious for an extended period of time and whose energy requirements are low because they are cold-blooded and have no need to generate heat. Different species of frog use a number of methods of moving around including jumping , running , walking , swimming , burrowing , climbing and gliding.

Frogs are generally recognized as exceptional jumpers and, relative to their size, the best jumpers of all vertebrates. Within a species, jump distance increases with increasing size, but relative jumping distance body-lengths jumped decreases. The Indian skipper frog Euphlyctis cyanophlyctis has the ability to leap out of the water from a position floating on the surface.

Slow-motion photography shows that the muscles have passive flexibility. They are first stretched while the frog is still in the crouched position, then they are contracted before being stretched again to launch the frog into the air.

The fore legs are folded against the chest and the hind legs remain in the extended, streamlined position for the duration of the jump. When the muscles contract, the energy is first transferred into the stretched tendon which is wrapped around the ankle bone. Then the muscles stretch again at the same time as the tendon releases its energy like a catapult to produce a powerful acceleration beyond the limits of muscle-powered acceleration.

Frogs in the families Bufonidae, Rhinophrynidae , and Microhylidae have short back legs and tend to walk rather than jump. The Great Plains narrow-mouthed toad Gastrophryne olivacea has been described as having a gait that is "a combination of running and short hops that are usually only an inch or two in length".

By measuring the toad's uptake of oxygen it was found that hopping was an inefficient use of resources during sustained locomotion but was a useful strategy during short bursts of high-intensity activity. The red-legged running frog Kassina maculata has short, slim hind limbs unsuited to jumping.

It can move fast by using a running gait in which the two hind legs are used alternately. Slow-motion photography shows, unlike a horse that can trot or gallop, the frog's gait remained similar at slow, medium, and fast speeds. Frogs that live in or visit water have adaptations that improve their swimming abilities.

The hind limbs are heavily muscled and strong. The webbing between the toes of the hind feet increases the area of the foot and helps propel the frog powerfully through the water. Members of the family Pipidae are wholly aquatic and show the most marked specialization. They have inflexible vertebral columns, flattened, streamlined bodies, lateral line systems, and powerful hind limbs with large webbed feet.

Some frogs have become adapted for burrowing and a life underground. They tend to have rounded bodies, short limbs, small heads with bulging eyes, and hind feet adapted for excavation.

An extreme example of this is the purple frog Nasikabatrachus sahyadrensis from southern India which feeds on termites and spends almost its whole life underground. It emerges briefly during the monsoon to mate and breed in temporary pools. It has a tiny head with a pointed snout and a plump, rounded body. Because of this fossorial existence, it was first described in , being new to the scientific community at that time, although previously known to local people. The spadefoot toads of North America are also adapted to underground life.

The Plains spadefoot toad Spea bombifrons is typical and has a flap of keratinised bone attached to one of the metatarsals of the hind feet which it uses to dig itself backwards into the ground. As it digs, the toad wriggles its hips from side to side to sink into the loose soil. It has a shallow burrow in the summer from which it emerges at night to forage.

In winter, it digs much deeper and has been recorded at a depth of 4. During this time, urea accumulates in its tissues and water is drawn in from the surrounding damp soil by osmosis to supply the toad's needs.

The burrowing frogs of Australia have a rather different lifestyle. The western spotted frog Heleioporus albopunctatus digs a burrow beside a river or in the bed of an ephemeral stream and regularly emerges to forage. Mating takes place and eggs are laid in a foam nest inside the burrow. The eggs partially develop there, but do not hatch until they are submerged following heavy rainfall. The tadpoles then swim out into the open water and rapidly complete their development.

One of these, the green burrowing frog Scaphiophryne marmorata , has a flattened head with a short snout and well-developed metatarsal tubercles on its hind feet to help with excavation. It also has greatly enlarged terminal discs on its fore feet that help it to clamber around in bushes. Tree frogs live high in the canopy , where they scramble around on the branches, twigs, and leaves, sometimes never coming down to earth.

The "true" tree frogs belong to the family Hylidae, but members of other frog families have independently adopted an arboreal habit, a case of convergent evolution. These include the glass frogs Centrolenidae , the bush frogs Hyperoliidae , some of the narrow-mouthed frogs Microhylidae , and the shrub frogs Rhacophoridae.

The surface of the toe pads is formed from a closely packed layer of flat-topped, hexagonal epidermal cells separated by grooves into which glands secrete mucus. These toe pads, moistened by the mucus, provide the grip on any wet or dry surface, including glass.

The forces involved include boundary friction of the toe pad epidermis on the surface and also surface tension and viscosity. The reticulated leaf frog Phyllomedusa ayeaye has a single opposed digit on each fore foot and two opposed digits on its hind feet. This allows it to grasp the stems of bushes as it clambers around in its riverside habitat.

During the evolutionary history of frogs, several different groups have independently taken to the air. Typical of them is Wallace's flying frog Rhacophorus nigropalmatus from Malaysia and Borneo. It has large feet with the fingertips expanded into flat adhesive discs and the digits fully webbed.

Flaps of skin occur on the lateral margins of the limbs and across the tail region. With the digits splayed, the limbs outstretched, and these flaps spread, it can glide considerable distances, but is unable to undertake powered flight. Like other amphibians, the life cycle of a frog normally starts in water with an egg that hatches into a limbless larva with gills, commonly known as a tadpole. After further growth, during which it develops limbs and lungs, the tadpole undergoes metamorphosis in which its appearance and internal organs are rearranged.

After this it is able to leave the water as a miniature, air-breathing frog. Two main types of reproduction occur in frogs, prolonged breeding and explosive breeding.

In the former, adopted by the majority of species, adult frogs at certain times of year assemble at a pond, lake or stream to breed. Many frogs return to the bodies of water in which they developed as larvae. This often results in annual migrations involving thousands of individuals. In explosive breeders, mature adult frogs arrive at breeding sites in response to certain trigger factors such as rainfall occurring in an arid area.

In these frogs, mating and spawning take place promptly and the speed of larval growth is rapid in order to make use of the ephemeral pools before they dry up. Among prolonged breeders, males usually arrive at the breeding site first and remain there for some time whereas females tend to arrive later and depart soon after they have spawned.

This means that males outnumber females at the water's edge and defend territories from which they expel other males. They advertise their presence by calling, often alternating their croaks with neighbouring frogs. Larger, stronger males tend to have deeper calls and maintain higher quality territories. Females select their mates at least partly on the basis of the depth of their voice. They may intercept females that are approaching a calling male or take over a vacated territory.

Calling is an energy-sapping activity. Sometimes the two roles are reversed and a calling male gives up its territory and becomes a satellite.

In explosive breeders, the first male that finds a suitable breeding location, such as a temporary pool, calls loudly and other frogs of both sexes converge on the pool. Explosive breeders tend to call in unison creating a chorus that can be heard from far away. The spadefoot toads Scaphiopus spp.

Mate selection and courtship is not as important as speed in reproduction. In some years, suitable conditions may not occur and the frogs may go for two or more years without breeding. At the breeding site, the male mounts the female and grips her tightly round the body.

Typically, amplexus takes place in the water, the female releases her eggs and the male covers them with sperm; fertilization is external. In many species such as the Great Plains toad Bufo cognatus , the male restrains the eggs with his back feet, holding them in place for about three minutes.

In these species, fertilization is internal and females give birth to fully developed juvenile frogs, except L. Frogs' embryos are typically surrounded by several layers of gelatinous material. When several eggs are clumped together, they are collectively known as frogspawn. The jelly provides support and protection while allowing the passage of oxygen, carbon dioxide and ammonia.

It absorbs moisture and swells on contact with water. After fertilization, the innermost portion liquifies to allow free movement of the developing embryo. In certain species, such as the Northern red-legged frog Rana aurora and the wood frog Rana sylvatica , symbiotic unicellular green algae are present in the gelatinous material.

It is thought that these may benefit the developing larvae by providing them with extra oxygen through photosynthesis. The shape and size of the egg mass is characteristic of the species. Ranids tend to produce globular clusters containing large numbers of eggs whereas bufonids produce long, cylindrical strings.

The tiny yellow-striped pygmy eleuth Eleutherodactylus limbatus lays eggs singly, burying them in moist soil. The eggs hatch when the nest is flooded, or the tadpoles may complete their development in the foam if flooding does not occur. Aquatic eggs normally hatch within one week when the capsule splits as a result of enzymes released by the developing larvae. The larvae that emerge from the eggs, known as tadpoles or occasionally polliwogs , typically have oval bodies and long, vertically flattened tails.

As a general rule, free-living larvae are fully aquatic, but at least one species Nannophrys ceylonensis has semiterrestrial tadpoles which live among wet rocks. From early in its development, a gill pouch covers the tadpole's gills and front legs. The lungs soon start to develop and are used as an accessory breathing organ. Some species go through metamorphosis while still inside the egg and hatch directly into small frogs.

Tadpoles lack true teeth, but the jaws in most species have two elongated, parallel rows of small, keratinized structures called keradonts in their upper jaws.

Their lower jaws usually have three rows of keradonts surrounded by a horny beak, but the number of rows can vary and the exact arrangements of mouth parts provide a means for species identification.

This has been suggested as an adaptation to their lifestyles; because the transformation into frogs happens very fast, the tail is made of soft tissue only, as bone and cartilage take a much longer time to be broken down and absorbed.

The tail fin and tip is fragile and will easily tear, which is seen as an adaptation to escape from predators which tries to grasp them by the tail. Tadpoles are typically herbivorous , feeding mostly on algae , including diatoms filtered from the water through the gills. Some species are carnivorous at the tadpole stage, eating insects, smaller tadpoles, and fish.

The Cuban tree frog Osteopilus septentrionalis is one of a number of species in which the tadpoles can be cannibalistic. Tadpoles that develop legs early may be eaten by the others, so late developers may have better long-term survival prospects. Tadpoles are highly vulnerable to being eaten by fish, newts , predatory diving beetles , and birds, such as kingfishers.

Some tadpoles, including those of the cane toad Bufo marinus , are poisonous. The tadpole stage may be as short as a week in explosive breeders or it may last through one or more winters followed by metamorphosis in the spring.

At the end of the tadpole stage, a frog undergoes metamorphosis in which its body makes a sudden transition into the adult form. This metamorphosis typically lasts only 24 hours, and is initiated by production of the hormone thyroxine.

This causes different tissues to develop in different ways. The principal changes that take place include the development of the lungs and the disappearance of the gills and gill pouch, making the front legs visible. The lower jaw transforms into the big mandible of the carnivorous adult, and the long, spiral gut of the herbivorous tadpole is replaced by the typical short gut of a predator.

The eardrum, middle ear, and inner ear are developed. The skin becomes thicker and tougher, the lateral line system is lost, and skin glands are developed. At this time, the tail is being lost and locomotion by means of limbs is only just becoming established. After metamorphosis, young adults may disperse into terrestrial habitats or continue to live in water. Almost all frog species are carnivorous as adults, preying on invertebrates, including arthropods , worms , snails , and slugs.

A few of the larger ones may eat other frogs, small mammals , and fish. Some frogs use their sticky tongues to catch fast-moving prey, while others push food into their mouths with their hands. A few species also eat plant matter; the tree frog Xenohyla truncata is partly herbivorous, its diet including a large proportion of fruit, [] Leptodactylus mystaceus has been found to eat plants, [] [] and folivory occurs in Euphlyctis hexadactylus , with plants constituting The northern leopard frog Rana pipiens is eaten by herons , hawks , fish, large salamanders , snakes , raccoons , skunks , mink , bullfrogs, and other animals.

Frogs are primary predators and an important part of the food web. Being cold-blooded , they make efficient use of the food they eat with little energy being used for metabolic processes, while the rest is transformed into biomass.

They are themselves eaten by secondary predators and are the primary terrestrial consumers of invertebrates, most of which feed on plants. By reducing herbivory, they play a part in increasing the growth of plants and are thus part of a delicately balanced ecosystem. Little is known about the longevity of frogs and toads in the wild, but some can live for many years. Skeletochronology is a method of examining bones to determine age. Using this method, the ages of mountain yellow-legged frogs Rana muscosa were studied, the phalanges of the toes showing seasonal lines where growth slows in winter.

The oldest frogs had ten bands, so their age was believed to be 14 years, including the four-year tadpole stage. The cane toad Bufo marinus has been known to survive 24 years in captivity, and the American bullfrog Rana catesbeiana 14 years. Those that breed in smaller water bodies tend to have greater and more complex parental care behaviour.

Once this happened, the desiccating terrestrial environment demands that one or both parents keep them moist to ensure their survival. In small pools, predators are mostly absent and competition between tadpoles becomes the variable that constrains their survival.

Certain frog species avoid this competition by making use of smaller phytotelmata water-filled leaf axils or small woody cavities as sites for depositing a few tadpoles. Frog species that changed from the use of larger to smaller phytotelmata have evolved a strategy of providing their offspring with nutritive but unfertilized eggs.

The male frog guards them from predation and carries water in his cloaca to keep them moist. When they hatch, the female moves the tadpoles on her back to a water-holding bromeliad or other similar water body, depositing just one in each location.

She visits them regularly and feeds them by laying one or two unfertilized eggs in the phytotelma, continuing to do this until the young are large enough to undergo metamorphosis. Many other diverse forms of parental care are seen in frogs.

The tiny male Colostethus subpunctatus stands guard over his egg cluster, laid under a stone or log. When the eggs hatch, he transports the tadpoles on his back to a temporary pool, where he partially immerses himself in the water and one or more tadpoles drop off.

He then moves on to another pool. He keeps them damp in dry weather by immersing himself in a pond, and prevents them from getting too wet in soggy vegetation by raising his hindquarters. After three to six weeks, he travels to a pond and the eggs hatch into tadpoles. The foam is made from proteins and lectins , and seems to have antimicrobial properties. The eggs are laid in the centre, followed by alternate layers of foam and eggs, finishing with a foam capping. Some frogs protect their offspring inside their own bodies.

Both male and female pouched frogs Assa darlingtoni guard their eggs, which are laid on the ground. When the eggs hatch, the male lubricates his body with the jelly surrounding them and immerses himself in the egg mass. The tadpoles wriggle into skin pouches on his side, where they develop until they metamorphose into juvenile frogs. She ceases to feed and stops secreting stomach acid. The tadpoles rely on the yolks of the eggs for nourishment. After six or seven weeks, they are ready for metamorphosis.

The mother regurgitates the tiny frogs, which hop away from her mouth.

What Animals Undergo Metamorphosis?