Frog

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This article is about the group of amphibians. Frog_sentence_0

For other uses, see Frog (disambiguation). Frog_sentence_1

Frog_table_infobox_0

Frogs

Temporal range: Early JurassicPresent, 200–0 Ma PreꞒ O S D C P T J K Pg NFrog_header_cell_0_0_0

Scientific classification AnuraFrog_header_cell_0_1_0
Kingdom:Frog_cell_0_2_0 AnimaliaFrog_cell_0_2_1
Phylum:Frog_cell_0_3_0 ChordataFrog_cell_0_3_1
Class:Frog_cell_0_4_0 AmphibiaFrog_cell_0_4_1
Clade:Frog_cell_0_5_0 SalientiaFrog_cell_0_5_1
Order:Frog_cell_0_6_0 Anura

Duméril, 1806 (as Anoures)Frog_cell_0_6_1

SubordersFrog_header_cell_0_7_0

A frog is any member of a diverse and largely carnivorous group of short-bodied, tailless amphibians composing the order Anura (literally without tail in Ancient Greek). Frog_sentence_2

The oldest fossil "proto-frog" appeared in the early Triassic of Madagascar, but molecular clock dating suggests their origins may extend further back to the Permian, 265 million years ago. Frog_sentence_3

Frogs are widely distributed, ranging from the tropics to subarctic regions, but the greatest concentration of species diversity is in tropical rainforest. Frog_sentence_4

There are over 6,300 recorded species, which account for around 88% of extant amphibian species. Frog_sentence_5

They are also one of the five most diverse vertebrate orders. Frog_sentence_6

Warty frog species tend to be called toads, but the distinction between frogs and toads is informal, not from taxonomy or evolutionary history. Frog_sentence_7

All toads are frogs, but not all frogs are toads. Frog_sentence_8

An adult frog has a stout body, protruding eyes, anteriorly-attached tongue, limbs folded underneath, and no tail (except in tailed frogs). Frog_sentence_9

Frogs have glandular skin, with secretions ranging from distasteful to toxic. Frog_sentence_10

Their skin varies in colour from well-camouflaged dappled brown, grey and green to vivid patterns of bright red or yellow and black to show toxicity and ward off predators. Frog_sentence_11

Adult frogs live in fresh water and on dry land; some species are adapted for living underground or in trees. Frog_sentence_12

Frogs typically lay their eggs in water. Frog_sentence_13

The eggs hatch into aquatic larvae called tadpoles that have tails and internal gills. Frog_sentence_14

They have highly specialized rasping mouth parts suitable for herbivorous, omnivorous or planktivorous diets. Frog_sentence_15

The life cycle is completed when they metamorphose into adults. Frog_sentence_16

A few species deposit eggs on land or bypass the tadpole stage. Frog_sentence_17

Adult frogs generally have a carnivorous diet consisting of small invertebrates, but omnivorous species exist and a few feed on plant matter. Frog_sentence_18

Frog skin has a rich microbiome which is important to their health. Frog_sentence_19

Frogs are extremely efficient at converting what they eat into body mass. Frog_sentence_20

They are an important food source for predators and part of the food web dynamics of many of the world's ecosystems. Frog_sentence_21

The skin is semi-permeable, making them susceptible to dehydration, so they either live in moist places or have special adaptations to deal with dry habitats. Frog_sentence_22

Frogs produce a wide range of vocalizations, particularly in their breeding season, and exhibit many different kinds of complex behaviors to attract mates, to fend off predators and to generally survive. Frog_sentence_23

Frogs are valued as food by humans and also have many cultural roles in literature, symbolism and religion. Frog_sentence_24

They are also seen as environmental bellwethers, with declines in frog populations often viewed as early warning signs of environmental damage. Frog_sentence_25

Frog populations have declined significantly since the 1950s. Frog_sentence_26

More than one third of species are considered to be threatened with extinction and over 120 are believed to have become extinct since the 1980s. Frog_sentence_27

The number of malformations among frogs is on the rise and an emerging fungal disease, chytridiomycosis, has spread around the world. Frog_sentence_28

Conservation biologists are working to understand the causes of these problems and to resolve them. Frog_sentence_29

Etymology and taxonomy Frog_section_0

The use of the common names "frog" and "toad" has no taxonomic justification. Frog_sentence_30

From a classification perspective, all members of the order Anura are frogs, but only members of the family Bufonidae are considered "true toads". Frog_sentence_31

The use of the term "frog" in common names usually refers to species that are aquatic or semi-aquatic and have smooth, moist skins; the term "toad" generally refers to species that are terrestrial with dry, warty skins. Frog_sentence_32

There are numerous exceptions to this rule. Frog_sentence_33

The European fire-bellied toad (Bombina bombina) has a slightly warty skin and prefers a watery habitat whereas the Panamanian golden frog (Atelopus zeteki) is in the toad family Bufonidae and has a smooth skin. Frog_sentence_34

Etymology Frog_section_1

The origin of the order name Anura—and its original spelling Anoures—is the Ancient Greek "alpha privative" prefix (an-) "without", and (ourá), meaning "animal tail". Frog_sentence_35

It refers to the tailless character of these amphibians. Frog_sentence_36

The origins of the word frog are uncertain and debated. Frog_sentence_37

The word is first attested in Old English as frogga, but the usual Old English word for the frog was frosc (with variants such as frox and forsc), and it is agreed that the word frog is somehow related to this. Frog_sentence_38

Old English frosc remained in dialectal use in English as frosh and frosk into the nineteenth century, and is paralleled widely in other Germanic languages, with examples in the modern languages including German Frosch, Icelandic froskur, and Dutch (kik)vors. Frog_sentence_39

These words allow us to reconstruct a Common Germanic ancestor *froskaz. Frog_sentence_40

The third edition of the Oxford English Dictionary finds that the etymology of *froskaz is uncertain, but agrees with arguments that it could plausibly derive from a Proto-Indo-European base along the lines of *preu = "jump". Frog_sentence_41

How Old English frosc gave rise to frogga is, however, uncertain, as the development does not involve a regular sound-change. Frog_sentence_42

Instead, it seems that there was a trend in Old English to coin nicknames for animals ending in -g, with examples—themselves all of uncertain etymology—including dog, hog, pig, stag, and (ear)wig. Frog_sentence_43

Frog appears to have been adapted from frosc as part of this trend. Frog_sentence_44

Meanwhile, the word toad, first attested as Old English tādige, is unique to English and is likewise of uncertain etymology. Frog_sentence_45

It is the basis for the word tadpole, first attested as Middle English taddepol, apparently meaning 'toad-head'. Frog_sentence_46

Taxonomy Frog_section_2

About 88% of amphibian species are classified in the order Anura. Frog_sentence_47

These include over 7,100 species in 55 families, of which the Craugastoridae (850 spp.), Hylidae (724 spp.), Microhylidae (688 spp.), and Bufonidae (621 spp.) are the richest in species. Frog_sentence_48

The Anura include all modern frogs and any fossil species that fit within the anuran definition. Frog_sentence_49

The characteristics of anuran adults include: 9 or fewer presacral vertebrae, the presence of a urostyle formed of fused vertebrae, no tail, a long and forward-sloping ilium, shorter fore limbs than hind limbs, radius and ulna fused, tibia and fibula fused, elongated ankle bones, absence of a prefrontal bone, presence of a hyoid plate, a lower jaw without teeth (with the exception of Gastrotheca guentheri) consisting of three pairs of bones (angulosplenial, dentary, and mentomeckelian, with the last pair being absent in Pipoidea), an unsupported tongue, lymph spaces underneath the skin, and a muscle, the protractor lentis, attached to the lens of the eye. Frog_sentence_50

The anuran larva or tadpole has a single central respiratory spiracle and mouthparts consisting of keratinous beaks and denticles. Frog_sentence_51

Frogs and toads are broadly classified into three suborders: 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 families of modern frogs, including most common species throughout the world. Frog_sentence_52

The suborder Neobatrachia is further divided into the two superfamilies Hyloidea and Ranoidea. Frog_sentence_53

This classification is based on such morphological features as the number of vertebrae, the structure of the pectoral girdle, and the morphology of tadpoles. Frog_sentence_54

While this classification is largely accepted, relationships among families of frogs are still debated. Frog_sentence_55

Some species of anurans hybridize readily. Frog_sentence_56

For instance, the edible frog (Pelophylax esculentus) is a hybrid between the pool frog (P. lessonae) and the marsh frog (P. ridibundus). Frog_sentence_57

The fire-bellied toads Bombina bombina and B. Frog_sentence_58 variegata are similar in forming hybrids. Frog_sentence_59

These are less fertile than their parents, giving rise to a hybrid zone where the hybrids are prevalent. Frog_sentence_60

Evolution Frog_section_3

The origins and evolutionary relationships between the three main groups of amphibians are hotly debated. Frog_sentence_61

A molecular phylogeny based on rDNA analysis dating from 2005 suggests that salamanders and caecilians are more closely related to each other than they are to frogs and the divergence of the three groups took place in the Paleozoic or early Mesozoic before the breakup of the supercontinent Pangaea and soon after their divergence from the lobe-finned fishes. Frog_sentence_62

This would help account for the relative scarcity of amphibian fossils from the period before the groups split. Frog_sentence_63

Another molecular phylogenetic analysis conducted about the same time concluded that lissamphibians first appeared about 330 million years ago and that the temnospondyl-origin hypothesis is more credible than other theories. Frog_sentence_64

The neobatrachians seemed to have originated in Africa/India, the salamanders in East Asia and the caecilians in tropical Pangaea. Frog_sentence_65

Other researchers, while agreeing with the main thrust of this study, questioned the choice of calibration points used to synchronise the data. Frog_sentence_66

They proposed that the date of lissamphibian diversification should be placed in the Permian, rather less than 300 million years ago, a date in better agreement with the palaeontological data. Frog_sentence_67

A further study in 2011 using both extinct and living taxa sampled for morphological, as well as molecular data, came to the conclusion that Lissamphibia is monophyletic and that it should be nested within Lepospondyli rather than within Temnospondyli. Frog_sentence_68

The study postulated that Lissamphibia originated no earlier than the late Carboniferous, some 290 to 305 million years ago. Frog_sentence_69

The split between Anura and Caudata was estimated as taking place 292 million years ago, rather later than most molecular studies suggest, with the caecilians splitting off 239 million years ago. Frog_sentence_70

In 2008, Gerobatrachus hottoni, a temnospondyl with many frog- and salamander-like characteristics, was discovered in Texas. Frog_sentence_71

It dated back 290 million years and was hailed as a missing link, a stem batrachian close to the common ancestor of frogs and salamanders, consistent with the widely accepted hypothesis that frogs and salamanders are more closely related to each other (forming a clade called Batrachia) than they are to caecilians. Frog_sentence_72

However, others have suggested that Gerobatrachus hottoni was only a dissorophoid temnospondyl unrelated to extant amphibians. Frog_sentence_73

Salientia (Latin salere (salio), "to jump") is the name of the total group that includes modern frogs in the order Anura as well as their close fossil relatives, the "proto-frogs" or "stem-frogs". Frog_sentence_74

The common features possessed by these proto-frogs include 14 presacral vertebrae (modern frogs have eight or 9), a long and forward-sloping ilium in the pelvis, the presence of a frontoparietal bone, and a lower jaw without teeth. Frog_sentence_75

The earliest known amphibians that were more closely related to frogs than to salamanders are Triadobatrachus massinoti, from the early Triassic period of Madagascar (about 250 million years ago), and Czatkobatrachus polonicus, from the Early Triassic of Poland (about the same age as Triadobatrachus). Frog_sentence_76

The skull of Triadobatrachus is frog-like, being broad with large eye sockets, but the fossil has features diverging from modern frogs. Frog_sentence_77

These include a longer body with more vertebrae. Frog_sentence_78

The tail has separate vertebrae unlike the fused urostyle or coccyx in modern frogs. Frog_sentence_79

The tibia and fibula bones are also separate, making it probable that Triadobatrachus was not an efficient leaper. Frog_sentence_80

The earliest known "true frogs" that fall into the anuran lineage proper all lived in the early Jurassic period. Frog_sentence_81

One such early frog species, Prosalirus bitis, was discovered in 1995 in the Kayenta Formation of Arizona and dates back to the Early Jurassic epoch (199.6 to 175 million years ago), making Prosalirus somewhat more recent than Triadobatrachus. Frog_sentence_82

Like the latter, Prosalirus did not have greatly enlarged legs, but had the typical three-pronged pelvic structure of modern frogs. Frog_sentence_83

Unlike Triadobatrachus, Prosalirus had already lost nearly all of its tail and was well adapted for jumping. Frog_sentence_84

Another Early Jurassic frog is Vieraella herbsti, which is known only from dorsal and ventral impressions of a single animal and was estimated to be 33 mm (1.3 in) from snout to vent. Frog_sentence_85

Notobatrachus degiustoi from the middle Jurassic is slightly younger, about 155–170 million years old. Frog_sentence_86

The main evolutionary changes in this species involved the shortening of the body and the loss of the tail. Frog_sentence_87

The evolution of modern Anura likely was complete by the Jurassic period. Frog_sentence_88

Since then, evolutionary changes in chromosome numbers have taken place about 20 times faster in mammals than in frogs, which means speciation is occurring more rapidly in mammals. Frog_sentence_89

According to genetic studies, the families Hyloidea, Microhylidae, and the clade Natatanura (comprising about 88% of living frogs) diversified simultaneously some 66 million years ago, soon after the Cretaceous–Paleogene extinction event associated with the Chicxulub impactor. Frog_sentence_90

All origins of arboreality (e.g. in Hyloidea and Natatanura) follow from that time and the resurgence of forest that occurred afterwards. Frog_sentence_91

Frog fossils have been found on all of the earth's continents. Frog_sentence_92

In 2020, it was announced that 40 million year old helmeted frog fossils had been discovered by a team of vertebrate paleontologists in Seymour Island on the Antarctic Peninsula, indicating that this region was once home to frogs related to those now living in South American Nothofagus forest. Frog_sentence_93

Phylogeny Frog_section_4

A cladogram showing the relationships of the different families of frogs in the clade Anura can be seen in the table below. Frog_sentence_94

This diagram, in the form of a tree, shows how each frog family is related to other families, with each node representing a point of common ancestry. Frog_sentence_95

It is based on Frost et al. Frog_sentence_96

(2006), Heinicke et al. Frog_sentence_97

(2009) and Pyron and Wiens (2011). Frog_sentence_98

Morphology and physiology Frog_section_5

Frogs have no tail, except as larvae, and most have long hind legs, elongated ankle bones, webbed toes, no claws, large eyes, and a smooth or warty skin. Frog_sentence_99

They have short vertebral columns, with no more than 10 free vertebrae and fused tailbones (urostyle or coccyx). Frog_sentence_100

Like other amphibians, oxygen can pass through their highly permeable skins. Frog_sentence_101

This unique feature allows them to remain in places without access to the air, respiring through their skins. Frog_sentence_102

Ribs are generally absent, so the lungs are filled by buccal pumping and a frog deprived of its lungs can maintain its body functions without them. Frog_sentence_103

For the skin to serve as a respiratory organ, it must remain moist. Frog_sentence_104

This makes frogs susceptible to various substances they may encounter in the environment, some of which may be toxic and can dissolve in the water film and be passed into their bloodstream. Frog_sentence_105

This may be one of the causes of the worldwide decline in frog populations. Frog_sentence_106

Frogs range in size from Paedophryne amauensis of Papua New Guinea that is 7.7 mm (0.30 in) in snout–to–vent length to the up to 32 cm (13 in) and 3.25 kg (7.2 lb) goliath frog (Conraua goliath) of central Africa. Frog_sentence_107

There are prehistoric, extinct species that reached even larger sizes. Frog_sentence_108

The skin hangs loosely on the body because of the lack of loose connective tissue. Frog_sentence_109

Frogs have three eyelid membranes: one is transparent to protect the eyes underwater, and two vary from translucent to opaque. Frog_sentence_110

They have a tympanum on each side of their heads which is involved in hearing and, in some species, is covered by skin. Frog_sentence_111

True toads completely lack teeth, but most frogs have them, specifically pedicellate teeth in which the crown is separated from the root by fibrous tissue. Frog_sentence_112

These are on the edge of the upper jaw and vomerine teeth are also on the roof of their mouths. Frog_sentence_113

No teeth are in the lower jaw and frogs usually swallow their food whole. Frog_sentence_114

The teeth are mainly used to grip the prey and keep it in place until swallowed, a process assisted by retracting the eyes into the head. Frog_sentence_115

The African bullfrog (Pyxicephalus), which preys on relatively large animals such as mice and other frogs, has cone shaped bony projections called odontoid processes at the front of the lower jaw which function like teeth. Frog_sentence_116

Feet and legs Frog_section_6

The structure of the feet and legs varies greatly among frog species, depending in part on whether they live primarily on the ground, in water, in trees, or in burrows. Frog_sentence_117

Frogs must be able to move quickly through their environment to catch prey and escape predators, and numerous adaptations help them to do so. Frog_sentence_118

Most frogs are either proficient at jumping or are descended from ancestors that were, with much of the musculoskeletal morphology modified for this purpose. Frog_sentence_119

The tibia, fibula, and tarsals have been fused into a single, strong bone, as have the radius and ulna in the fore limbs (which must absorb the impact on landing). Frog_sentence_120

The metatarsals have become elongated to add to the leg length and allow frogs to push against the ground for a longer period on take-off. Frog_sentence_121

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. Frog_sentence_122

The tail vertebrae have fused into a urostyle which is retracted inside the pelvis. Frog_sentence_123

This enables the force to be transferred from the legs to the body during a leap. Frog_sentence_124

The muscular system has been similarly modified. Frog_sentence_125

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. Frog_sentence_126

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. Frog_sentence_127

The muscles have also been greatly enlarged, with the main leg muscles accounting for over 17% of the total mass of frogs. Frog_sentence_128

Many frogs have webbed feet and the degree of webbing is directly proportional to the amount of time the species spends in the water. Frog_sentence_129

The completely aquatic African dwarf frog (Hymenochirus sp.) has fully webbed toes, whereas those of White's tree frog (Litoria caerulea), an arboreal species, are only a quarter or half webbed. Frog_sentence_130

Exceptions include flying frogs in the Hylidae and Rhacophoridae, which also have fully webbed toes used in gliding. Frog_sentence_131

Arboreal frogs have pads located on the ends of their toes to help grip vertical surfaces. Frog_sentence_132

These are not suction pads, the surface consisting instead of columnar cells with flat tops with small gaps between them lubricated by mucous glands. Frog_sentence_133

When the frog applies pressure, the cells adhere to irregularities on the surface and the grip is maintained through surface tension. Frog_sentence_134

This allows the frog to climb on smooth surfaces, but the system does not function efficiently when the pads are excessively wet. Frog_sentence_135

In many arboreal frogs, a small "intercalary structure" on each toe increases the surface area touching the substrate. Frog_sentence_136

Furthermore, many arboreal frogs have hip joints that allow both hopping and walking. Frog_sentence_137

Some frogs that live high in trees even possess an elaborate degree of webbing between their toes. Frog_sentence_138

This allows the frogs to "parachute" or make a controlled glide from one position in the canopy to another. Frog_sentence_139

Ground-dwelling frogs generally lack the adaptations of aquatic and arboreal frogs. Frog_sentence_140

Most have smaller toe pads, if any, and little webbing. Frog_sentence_141

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. Frog_sentence_142

Sometimes during the tadpole stage, one of the developing rear legs is eaten by a predator such as a dragonfly nymph. Frog_sentence_143

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. Frog_sentence_144

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 one or more extra legs. Frog_sentence_145

Skin Frog_section_7

A frog's skin is protective, has a respiratory function, can absorb water, and helps control body temperature. Frog_sentence_146

It has many glands, particularly on the head and back, which often exude distasteful and toxic substances (granular glands). Frog_sentence_147

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. Frog_sentence_148

The skin is shed every few weeks. Frog_sentence_149

It usually splits down the middle of the back and across the belly, and the frog pulls its arms and legs free. Frog_sentence_150

The sloughed skin is then worked towards the head where it is quickly eaten. Frog_sentence_151

Being cold-blooded, frogs have to adopt suitable behaviour patterns to regulate their temperature. Frog_sentence_152

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. Frog_sentence_153

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. Frog_sentence_154

The colour of a frog's skin is used for thermoregulation. Frog_sentence_155

In cool damp conditions, the colour will be darker than on a hot dry day. Frog_sentence_156

The grey foam-nest tree frog (Chiromantis xerampelina) is even able to turn white to minimize the chance of overheating. Frog_sentence_157

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. Frog_sentence_158

Glands located all over the body exude mucus which helps keep the skin moist and reduces evaporation. Frog_sentence_159

Some glands on the hands and chest of males are specialized to produce sticky secretions to aid in amplexus. Frog_sentence_160

Similar glands in tree frogs produce a glue-like substance on the adhesive discs of the feet. Frog_sentence_161

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. Frog_sentence_162

Other frogs have adopted behaviours to conserve water, including becoming nocturnal and resting in a water-conserving position. Frog_sentence_163

Some frogs may also rest in large groups with each frog pressed against its neighbours. Frog_sentence_164

This reduces the amount of skin exposed to the air or a dry surface, and thus reduces water loss. Frog_sentence_165

Woodhouse's toad (Bufo woodhousii), if given access to water after confinement in a dry location, sits in the shallows to rehydrate. Frog_sentence_166

The male hairy frog (Trichobatrachus robustus) has dermal papillae projecting from its lower back and thighs, giving it a bristly appearance. Frog_sentence_167

They contain blood vessels and are thought to increase the area of the skin available for respiration. Frog_sentence_168

Some species have bony plates embedded in their skin, a trait that appears to have evolved independently several times. Frog_sentence_169

In certain other species, the skin at the top of the head is compacted and the connective tissue of the dermis is co-ossified with the bones of the skull (exostosis). Frog_sentence_170

Camouflage is a common defensive mechanism in frogs. Frog_sentence_171

Most camouflaged frogs are nocturnal; during the day, they seek out a position where they can blend into the background and remain undetected. Frog_sentence_172

Some frogs have the ability to change colour, but this is usually restricted to a small range of colours. Frog_sentence_173

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. Frog_sentence_174

Features such as warts and skin folds are usually on ground-dwelling frogs, for whom smooth skin would not provide such effective camouflage. Frog_sentence_175

Certain frogs change colour between night and day, as light and moisture stimulate the pigment cells and cause them to expand or contract. Frog_sentence_176

Some are even able to control their skin texture. Frog_sentence_177

Frog_unordered_list_0

  • Frog_item_0_0
  • Frog_item_0_1

Respiration and circulation Frog_section_8

The skin of a frog is permeable to oxygen and carbon dioxide, as well as to water. Frog_sentence_178

There are blood vessels near the surface of the skin and when a frog is underwater, oxygen diffuses directly into the blood. Frog_sentence_179

When not submerged, a frog breathes by a process known as buccal pumping. Frog_sentence_180

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. Frog_sentence_181

Instead, it puffs out its throat and draws air in through the nostrils, which in many species can then be closed by valves. Frog_sentence_182

When the floor of the mouth is compressed, air is forced into the lungs. Frog_sentence_183

The fully aquatic Bornean flat-headed frog (Barbourula kalimantanensis) is the first frog known to lack lungs entirely. Frog_sentence_184

Frogs have three-chambered hearts, a feature they share with lizards. Frog_sentence_185

Oxygenated blood from the lungs and de-oxygenated blood from the respiring tissues enter the heart through separate atria. Frog_sentence_186

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. Frog_sentence_187

The ventricle is partially divided into narrow cavities which minimizes the mixing of the two types of blood. Frog_sentence_188

These features enable frogs to have a higher metabolic rate and be more active than would otherwise be possible. Frog_sentence_189

Some species of frog have adaptations that allow them to survive in oxygen deficient water. Frog_sentence_190

The Titicaca water frog (Telmatobius culeus) is one such species and has wrinkly skin that increases its surface area to enhance gas exchange. Frog_sentence_191

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. Frog_sentence_192

Digestion and excretion Frog_section_9

Frogs have maxillary teeth along their upper jaw which are used to hold food before it is swallowed. Frog_sentence_193

These teeth are very weak, and cannot be used to chew or catch and harm agile prey. Frog_sentence_194

Instead, the frog uses its sticky, cleft tongue to catch flies and other small moving prey. Frog_sentence_195

The tongue normally lies coiled in the mouth, free at the back and attached to the mandible at the front. Frog_sentence_196

It can be shot out and retracted at great speed. Frog_sentence_197

Some frogs have no tongue and just stuff food into their mouths with their hands. Frog_sentence_198

The eyes assist in the swallowing of food as they can be retracted through holes in the skull and help push food down the throat. Frog_sentence_199

The food then moves through the oesophagus into the stomach where digestive enzymes are added and it is churned up. Frog_sentence_200

It then proceeds to the small intestine (duodenum and ileum) where most digestion occurs. Frog_sentence_201

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. Frog_sentence_202

The food residue passes into the large intestine where excess water is removed and the wastes are passed out through the cloaca. Frog_sentence_203

The recently discovered Prometheus Frog has been reported to sometimes eat cooked or burnt food from areas affected by forest fires. Frog_sentence_204

Although adapted to terrestrial life, frogs resemble freshwater fish in their inability to conserve body water effectively. Frog_sentence_205

When they are on land, much water is lost by evaporation from the skin. Frog_sentence_206

The excretory system is similar to that of mammals and there are two kidneys that remove nitrogenous products from the blood. Frog_sentence_207

Frogs produce large quantities of dilute urine in order to flush out toxic products from the kidney tubules. Frog_sentence_208

The nitrogen is excreted as ammonia by tadpoles and aquatic frogs but mainly as urea, a less toxic product, by most terrestrial adults. Frog_sentence_209

A few species of tree frog with little access to water excrete the even less toxic uric acid. Frog_sentence_210

The urine passes along paired ureters to the urinary bladder from which it is vented periodically into the cloaca. Frog_sentence_211

All bodily wastes exit the body through the cloaca which terminates in a cloacal vent. Frog_sentence_212

Reproductive system Frog_section_10

See also: Sexual selection in amphibians Frog_sentence_213

In the male frog, the two testes are attached to the kidneys and semen passes into the kidneys through fine tubes called efferent ducts. Frog_sentence_214

It then travels on through the ureters, which are consequently known as urinogenital ducts. Frog_sentence_215

There is no penis, and sperm is ejected from the cloaca directly onto the eggs as the female lays them. Frog_sentence_216

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. Frog_sentence_217

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. Frog_sentence_218

This position is called amplexus and may be held for several days. Frog_sentence_219

The male frog has certain hormone-dependent secondary sexual characteristics. Frog_sentence_220

These include the development of special pads on his thumbs in the breeding season, to give him a firm hold. Frog_sentence_221

The grip of the male frog during amplexus stimulates the female to release eggs, usually wrapped in jelly, as spawn. Frog_sentence_222

In many species the male is smaller and slimmer than the female. Frog_sentence_223

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. Frog_sentence_224

Nervous system Frog_section_11

Frogs have a highly developed nervous system that consists of a brain, spinal cord and nerves. Frog_sentence_225

Many parts of frog brains correspond with those of humans. Frog_sentence_226

It consists of two olfactory lobes, two cerebral hemispheres, a pineal body, two optic lobes, a cerebellum and a medulla oblongata. Frog_sentence_227

Muscular coordination and posture are controlled by the cerebellum, and the medulla oblongata regulates respiration, digestion and other automatic functions. Frog_sentence_228

The relative size of the cerebrum in frogs is much smaller than it is in humans. Frog_sentence_229

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. Frog_sentence_230

By contrast, all amniotes (mammals, birds and reptiles) have twelve pairs of cranial nerves. Frog_sentence_231

Sight Frog_section_12

The eyes of most frogs are located on either side of the head near the top and project outwards as hemispherical bulges. Frog_sentence_232

They provide binocular vision over a field of 100° to the front and a total visual field of almost 360°. Frog_sentence_233

They may be the only part of an otherwise submerged frog to protrude from the water. Frog_sentence_234

Each eye has closable upper and lower lids and a nictitating membrane which provides further protection, especially when the frog is swimming. Frog_sentence_235

Members of the aquatic family Pipidae have the eyes located at the top of the head, a position better suited for detecting prey in the water above. Frog_sentence_236

The irises come in a range of colours and the pupils in a range of shapes. Frog_sentence_237

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.) has triangular pupils and the tomato frog (Dyscophus spp.) has circular ones. Frog_sentence_238

The irises of the southern toad (Anaxyrus terrestris) are patterned so as to blend in with the surrounding camouflaged skin. Frog_sentence_239

The distant vision of a frog is better than its near vision. Frog_sentence_240

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. Frog_sentence_241

When a frog shoots out its tongue to catch an insect it is reacting to a small moving object that it cannot see well and must line it up precisely beforehand because it shuts its eyes as the tongue is extended. Frog_sentence_242

Although it was formerly debated, more recent research has shown that frogs can see in colour, even in very low light. Frog_sentence_243

Hearing Frog_section_13

Frogs can hear both in the air and below water. Frog_sentence_244

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. Frog_sentence_245

The size and distance apart of the eardrums is related to the frequency and wavelength at which the frog calls. Frog_sentence_246

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. Frog_sentence_247

A noise causes the tympanum to vibrate and the sound is transmitted to the middle and inner ear. Frog_sentence_248

The middle ear contains semicircular canals which help control balance and orientation. Frog_sentence_249

In the inner ear, the auditory hair cells are arranged in two areas of the cochlea, the basilar papilla and the amphibian papilla. Frog_sentence_250

The former detects high frequencies and the latter low frequencies. Frog_sentence_251

Because the cochlea is short, frogs use electrical tuning to extend their range of audible frequencies and help discriminate different sounds. Frog_sentence_252

This arrangement enables detection of the territorial and breeding calls of their conspecifics. Frog_sentence_253

In some species that inhabit arid regions, the sound of thunder or heavy rain may arouse them from a dormant state. Frog_sentence_254

A frog may be startled by an unexpected noise but it will not usually take any action until it has located the source of the sound by sight. Frog_sentence_255

Call Frog_section_14

See also: Sexual selection in frogs Frog_sentence_256

The call or croak of a frog is unique to its species. Frog_sentence_257

Frogs create this sound by passing air through the larynx in the throat. Frog_sentence_258

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. Frog_sentence_259

Some frog calls are so loud that they can be heard up to a mile away. Frog_sentence_260

Additionally, some species have been found to use man-made structures such as drain pipes for artificial amplification of their call. Frog_sentence_261

Frogs in the genera Heleioporus and Neobatrachus lack vocal sacs but can still produce a loud call. Frog_sentence_262

Their buccal cavity is enlarged and dome-shaped, acting as a resonance chamber that amplifies the sound. Frog_sentence_263

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. Frog_sentence_264

They need to use an alternative means to communicate. Frog_sentence_265

The coastal tailed frog (Ascaphus truei) lives in mountain streams in North America and does not vocalize. Frog_sentence_266

The main reason for calling is to allow male frogs to attract a mate. Frog_sentence_267

Males may call individually or there may be a chorus of sound where numerous males have converged on breeding sites. Frog_sentence_268

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. Frog_sentence_269

Female frogs prefer males that produce sounds of greater intensity and lower frequency, attributes that stand out in a crowd. Frog_sentence_270

The rationale for this is thought to be that by demonstrating his prowess, the male shows his fitness to produce superior offspring. Frog_sentence_271

A different call is emitted by a male frog or unreceptive female when mounted by another male. Frog_sentence_272

This is a distinct chirruping sound and is accompanied by a vibration of the body. Frog_sentence_273

Tree frogs and some non-aquatic species have a rain call that they make on the basis of humidity cues prior to a shower. Frog_sentence_274

Many species also have a territorial call that is used to drive away other males. Frog_sentence_275

All of these calls are emitted with the mouth of the frog closed. Frog_sentence_276

A distress call, emitted by some frogs when they are in danger, is produced with the mouth open resulting in a higher-pitched call. Frog_sentence_277

It is typically used when the frog has been grabbed by a predator and may serve to distract or disorient the attacker so that it releases the frog. Frog_sentence_278

Many species of frog have deep calls. Frog_sentence_279

The croak of the American bullfrog (Rana catesbiana) is sometimes written as "jug o' rum". Frog_sentence_280

The Pacific tree frog (Pseudacris regilla) produces the onomatopoeic "ribbit" often heard in films. Frog_sentence_281

Other renderings of frog calls into speech include "brekekekex koax koax", the call of the marsh frog (Pelophylax ridibundus) in The Frogs, an Ancient Greek comic drama by Aristophanes. Frog_sentence_282

The calls of the Concave-eared torrent frog (Amolops tormotus) are unusual in many aspects. Frog_sentence_283

The males are notable for their varieties of calls where upward and downward frequency modulations take place. Frog_sentence_284

When they communicate, they produce calls that fall in the ultrasound frequency range. Frog_sentence_285

The last aspect that makes this species of frog's calls unusual is that nonlinear acoustic phenomena are important components in their acoustic signals. Frog_sentence_286

Torpor Frog_section_15

During extreme conditions, some frogs enter a state of torpor and remain inactive for months. Frog_sentence_287

In colder regions, many species of frog hibernate in winter. Frog_sentence_288

Those that live on land such as the American toad (Bufo americanus) dig a burrow and make a hibernaculum in which to lie dormant. Frog_sentence_289

Others, less proficient at digging, find a crevice or bury themselves in dead leaves. Frog_sentence_290

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. Frog_sentence_291

Their metabolism slows down and they live on their energy reserves. Frog_sentence_292

Some frogs such as the wood frog or spring peeper can even survive being frozen. Frog_sentence_293

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. Frog_sentence_294

An apparently lifeless, frozen frog can resume respiration and its heartbeat can restart when conditions warm up. Frog_sentence_295

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. Frog_sentence_296

It burrows underground and curls up inside a protective cocoon formed by its shed skin. Frog_sentence_297

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. Frog_sentence_298

This means that the limited amount of energy available to the comatose frog is used in a more efficient manner. Frog_sentence_299

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. Frog_sentence_300

Other research showed that, to provide these energy requirements, muscles atrophy, but hind limb muscles are preferentially unaffected. Frog_sentence_301

Frogs have been found to have upper critical temperatures of around 41 degrees Celsius. Frog_sentence_302

Locomotion Frog_section_16

Different species of frog use a number of methods of moving around including jumping, running, walking, swimming, burrowing, climbing and gliding. Frog_sentence_303

Frog_description_list_1

Frogs are generally recognized as exceptional jumpers and, relative to their size, the best jumpers of all vertebrates. Frog_sentence_304

The striped rocket frog, Litoria nasuta, can leap over 2 metres (6 ft 7 in), a distance that is more than fifty times its body length of 5.5 centimetres (2.2 in). Frog_sentence_305

There are tremendous differences between species in jumping capability. Frog_sentence_306

Within a species, jump distance increases with increasing size, but relative jumping distance (body-lengths jumped) decreases. Frog_sentence_307

The Indian skipper frog (Euphlyctis cyanophlyctis) has the ability to leap out of the water from a position floating on the surface. Frog_sentence_308

The tiny northern cricket frog (Acris crepitans) can "skitter" across the surface of a pond with a series of short rapid jumps. Frog_sentence_309

Slow-motion photography shows that the muscles have passive flexibility. Frog_sentence_310

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. Frog_sentence_311

The fore legs are folded against the chest and the hind legs remain in the extended, streamlined position for the duration of the jump. Frog_sentence_312

In some extremely capable jumpers, such as the Cuban tree frog (Osteopilus septentrionalis) and the northern leopard frog (Rana pipiens), the peak power exerted during a jump can exceed that which the muscle is theoretically capable of producing. Frog_sentence_313

When the muscles contract, the energy is first transferred into the stretched tendon which is wrapped around the ankle bone. Frog_sentence_314

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. Frog_sentence_315

A similar mechanism has been documented in locusts and grasshoppers. Frog_sentence_316

Early hatching of froglets can have negative effects on frog jumping performance and overall locomotion. Frog_sentence_317

The hindlimbs are unable to completely form, which results in them being shorter and much weaker relative to a normal hatching froglet. Frog_sentence_318

Early hatching froglets may tend to depend on other forms of locomotion more often, such as swimming and walking. Frog_sentence_319

Frog_description_list_2

Frogs in the families Bufonidae, Rhinophrynidae, and Microhylidae have short back legs and tend to walk rather than jump. Frog_sentence_320

When they try to move rapidly, they speed up the rate of movement of their limbs or resort to an ungainly hopping gait. Frog_sentence_321

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". Frog_sentence_322

In an experiment, Fowler's toad (Bufo fowleri) was placed on a treadmill which was turned at varying speeds. Frog_sentence_323

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. Frog_sentence_324

The red-legged running frog (Kassina maculata) has short, slim hind limbs unsuited to jumping. Frog_sentence_325

It can move fast by using a running gait in which the two hind legs are used alternately. Frog_sentence_326

Slow-motion photography shows, unlike a horse that can trot or gallop, the frog's gait remained similar at slow, medium, and fast speeds. Frog_sentence_327

This species can also climb trees and shrubs, and does so at night to catch insects. Frog_sentence_328

The Indian skipper frog (Euphlyctis cyanophlyctis) has broad feet and can run across the surface of the water for several metres (yards). Frog_sentence_329

Frog_description_list_3

Frogs that live in or visit water have adaptations that improve their swimming abilities. Frog_sentence_330

The hind limbs are heavily muscled and strong. Frog_sentence_331

The webbing between the toes of the hind feet increases the area of the foot and helps propel the frog powerfully through the water. Frog_sentence_332

Members of the family Pipidae are wholly aquatic and show the most marked specialization. Frog_sentence_333

They have inflexible vertebral columns, flattened, streamlined bodies, lateral line systems, and powerful hind limbs with large webbed feet. Frog_sentence_334

Tadpoles mostly have large tail fins which provide thrust when the tail is moved from side to side. Frog_sentence_335

Frog_description_list_4

Some frogs have become adapted for burrowing and a life underground. Frog_sentence_336

They tend to have rounded bodies, short limbs, small heads with bulging eyes, and hind feet adapted for excavation. Frog_sentence_337

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. Frog_sentence_338

It emerges briefly during the monsoon to mate and breed in temporary pools. Frog_sentence_339

It has a tiny head with a pointed snout and a plump, rounded body. Frog_sentence_340

Because of this fossorial existence, it was first described in 2003, being new to the scientific community at that time, although previously known to local people. Frog_sentence_341

The spadefoot toads of North America are also adapted to underground life. Frog_sentence_342

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. Frog_sentence_343

As it digs, the toad wriggles its hips from side to side to sink into the loose soil. Frog_sentence_344

It has a shallow burrow in the summer from which it emerges at night to forage. Frog_sentence_345

In winter, it digs much deeper and has been recorded at a depth of 4.5 m (15 ft). Frog_sentence_346

The tunnel is filled with soil and the toad hibernates in a small chamber at the end. Frog_sentence_347

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. Frog_sentence_348

Spadefoot toads are "explosive breeders", all emerging from their burrows at the same time and converging on temporary pools, attracted to one of these by the calling of the first male to find a suitable breeding location. Frog_sentence_349

The burrowing frogs of Australia have a rather different lifestyle. Frog_sentence_350

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. Frog_sentence_351

Mating takes place and eggs are laid in a foam nest inside the burrow. Frog_sentence_352

The eggs partially develop there, but do not hatch until they are submerged following heavy rainfall. Frog_sentence_353

The tadpoles then swim out into the open water and rapidly complete their development. Frog_sentence_354

Madagascan burrowing frogs are less fossorial and mostly bury themselves in leaf litter. Frog_sentence_355

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. Frog_sentence_356

It also has greatly enlarged terminal discs on its fore feet that help it to clamber around in bushes. Frog_sentence_357

It breeds in temporary pools that form after rains. Frog_sentence_358

Frog_description_list_5

Tree frogs live high in the canopy, where they scramble around on the branches, twigs, and leaves, sometimes never coming down to earth. Frog_sentence_359

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. Frog_sentence_360

These include the glass frogs (Centrolenidae), the bush frogs (Hyperoliidae), some of the narrow-mouthed frogs (Microhylidae), and the shrub frogs (Rhacophoridae). Frog_sentence_361

Most tree frogs are under 10 cm (4 in) in length, with long legs and long toes with adhesive pads on the tips. Frog_sentence_362

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. Frog_sentence_363

These toe pads, moistened by the mucus, provide the grip on any wet or dry surface, including glass. Frog_sentence_364

The forces involved include boundary friction of the toe pad epidermis on the surface and also surface tension and viscosity. Frog_sentence_365

Tree frogs are very acrobatic and can catch insects while hanging by one toe from a twig or clutching onto the blade of a windswept reed. Frog_sentence_366

Some members of the subfamily Phyllomedusinae have opposable toes on their feet. Frog_sentence_367

The reticulated leaf frog (Phyllomedusa ayeaye) has a single opposed digit on each fore foot and two opposed digits on its hind feet. Frog_sentence_368

This allows it to grasp the stems of bushes as it clambers around in its riverside habitat. Frog_sentence_369

Frog_description_list_6

During the evolutionary history of frogs, several different groups have independently taken to the air. Frog_sentence_370

Some frogs in the tropical rainforest are specially adapted for gliding from tree to tree or parachuting to the forest floor. Frog_sentence_371

Typical of them is Wallace's flying frog (Rhacophorus nigropalmatus) from Malaysia and Borneo. Frog_sentence_372

It has large feet with the fingertips expanded into flat adhesive discs and the digits fully webbed. Frog_sentence_373

Flaps of skin occur on the lateral margins of the limbs and across the tail region. Frog_sentence_374

With the digits splayed, the limbs outstretched, and these flaps spread, it can glide considerable distances, but is unable to undertake powered flight. Frog_sentence_375

It can alter its direction of travel and navigate distances of up to 15 m (49 ft) between trees. Frog_sentence_376

Life history Frog_section_17

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. Frog_sentence_377

After further growth, during which it develops limbs and lungs, the tadpole undergoes metamorphosis in which its appearance and internal organs are rearranged. Frog_sentence_378

After this it is able to leave the water as a miniature, air-breathing frog. Frog_sentence_379

Direct development, where eggs hatch into juveniles like small adults, is also known in many frogs, for example, Ischnocnema henselii, Eleutherodactylus coqui, and Raorchestes ochlandrae and Raorchestes chalazodes. Frog_sentence_380

Reproduction Frog_section_18

Two main types of reproduction occur in frogs, prolonged breeding and explosive breeding. Frog_sentence_381

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. Frog_sentence_382

Many frogs return to the bodies of water in which they developed as larvae. Frog_sentence_383

This often results in annual migrations involving thousands of individuals. Frog_sentence_384

In explosive breeders, mature adult frogs arrive at breeding sites in response to certain trigger factors such as rainfall occurring in an arid area. Frog_sentence_385

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. Frog_sentence_386

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. Frog_sentence_387

This means that males outnumber females at the water's edge and defend territories from which they expel other males. Frog_sentence_388

They advertise their presence by calling, often alternating their croaks with neighbouring frogs. Frog_sentence_389

Larger, stronger males tend to have deeper calls and maintain higher quality territories. Frog_sentence_390

Females select their mates at least partly on the basis of the depth of their voice. Frog_sentence_391

In some species there are satellite males who have no territory and do not call. Frog_sentence_392

They may intercept females that are approaching a calling male or take over a vacated territory. Frog_sentence_393

Calling is an energy-sapping activity. Frog_sentence_394

Sometimes the two roles are reversed and a calling male gives up its territory and becomes a satellite. Frog_sentence_395

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. Frog_sentence_396

Explosive breeders tend to call in unison creating a chorus that can be heard from far away. Frog_sentence_397

The spadefoot toads (Scaphiopus spp.) of North America fall into this category. Frog_sentence_398

Mate selection and courtship is not as important as speed in reproduction. Frog_sentence_399

In some years, suitable conditions may not occur and the frogs may go for two or more years without breeding. Frog_sentence_400

Some female New Mexico spadefoot toads (Spea multiplicata) only spawn half of the available eggs at a time, perhaps retaining some in case a better reproductive opportunity arises later. Frog_sentence_401

At the breeding site, the male mounts the female and grips her tightly round the body. Frog_sentence_402

Typically, amplexus takes place in the water, the female releases her eggs and the male covers them with sperm; fertilization is external. Frog_sentence_403

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. Frog_sentence_404

Members of the West African genus Nimbaphrynoides are unique among frogs in that they are viviparous; Limnonectes larvaepartus, Eleutherodactylus jasperi and members of the Tanzanian genus Nectophrynoides are the only frogs known to be ovoviviparous. Frog_sentence_405

In these species, fertilization is internal and females give birth to fully developed juvenile frogs, except L. larvaepartus, which give birth to tadpoles. Frog_sentence_406

Life cycle Frog_section_19

Eggs / frogspawn Frog_section_20

Frogs' embryos are typically surrounded by several layers of gelatinous material. Frog_sentence_407

When several eggs are clumped together, they are collectively known as . Frog_sentence_408

The jelly provides support and protection while allowing the passage of oxygen, carbon dioxide and ammonia. Frog_sentence_409

It absorbs moisture and swells on contact with water. Frog_sentence_410

After fertilization, the innermost portion liquifies to allow free movement of the developing embryo. Frog_sentence_411

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. Frog_sentence_412

It is thought that these may benefit the developing larvae by providing them with extra oxygen through photosynthesis. Frog_sentence_413

Most eggs are black or dark brown and this has the advantage of absorbing warmth from the sun which the insulating capsule retains. Frog_sentence_414

The interior of globular egg clusters of the wood frog (Rana sylvatica) has been found to be up to 6 °C (11 °F) warmer than the surrounding water and this speeds up the development of the larvae. Frog_sentence_415

The shape and size of the egg mass is characteristic of the species. Frog_sentence_416

Ranids tend to produce globular clusters containing large numbers of eggs whereas bufonids produce long, cylindrical strings. Frog_sentence_417

The tiny yellow-striped pygmy eleuth (Eleutherodactylus limbatus) lays eggs singly, burying them in moist soil. Frog_sentence_418

The smoky jungle frog (Leptodactylus pentadactylus) makes a nest of foam in a hollow. Frog_sentence_419

The eggs hatch when the nest is flooded, or the tadpoles may complete their development in the foam if flooding does not occur. Frog_sentence_420

The red-eyed treefrog (Agalychnis callidryas) deposits its eggs on a leaf above a pool and when they hatch, the larvae fall into the water below. Frog_sentence_421

The larvae developing in the eggs can detect vibrations caused by nearby predatory wasps or snakes, and will hatch early to avoid being eaten. Frog_sentence_422

In general, the length of the egg stage depends on the species and the environmental conditions. Frog_sentence_423

Aquatic eggs normally hatch within one week when the capsule splits as a result of enzymes released by the developing larvae. Frog_sentence_424

Tadpoles Frog_section_21

The larvae that emerge from the eggs, known as tadpoles (or occasionally polliwogs), typically have oval bodies and long, vertically flattened tails. Frog_sentence_425

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. Frog_sentence_426

Tadpoles lack eyelids and have cartilaginous skeletons, lateral line systems, gills for respiration (external gills at first, internal gills later), and vertically flattened tails they use for swimming. Frog_sentence_427

From early in its development, a gill pouch covers the tadpole's gills and front legs. Frog_sentence_428

The lungs soon start to develop and are used as an accessory breathing organ. Frog_sentence_429

Some species go through metamorphosis while still inside the egg and hatch directly into small frogs. Frog_sentence_430

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. Frog_sentence_431

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. Frog_sentence_432

In the Pipidae, with the exception of Hymenochirus, the tadpoles have paired anterior barbels, which make them resemble small catfish. Frog_sentence_433

Their tails are stiffened by a notochord, but does not contain any bony or cartilaginous elements except for a few vertebrae at the base which forms the urostyle during metamorphosis. Frog_sentence_434

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. Frog_sentence_435

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. Frog_sentence_436

Tadpoles are typically herbivorous, feeding mostly on algae, including diatoms filtered from the water through the gills. Frog_sentence_437

Some species are carnivorous at the tadpole stage, eating insects, smaller tadpoles, and fish. Frog_sentence_438

The Cuban tree frog (Osteopilus septentrionalis) is one of a number of species in which the tadpoles can be cannibalistic. Frog_sentence_439

Tadpoles that develop legs early may be eaten by the others, so late developers may have better long-term survival prospects. Frog_sentence_440

Tadpoles are highly vulnerable to being eaten by fish, newts, predatory diving beetles, and birds, such as kingfishers. Frog_sentence_441

Some tadpoles, including those of the cane toad (Bufo marinus), are poisonous. Frog_sentence_442

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. Frog_sentence_443

Metamorphosis Frog_section_22

At the end of the tadpole stage, a frog undergoes metamorphosis in which its body makes a sudden transition into the adult form. Frog_sentence_444

This metamorphosis typically lasts only 24 hours, and is initiated by production of the hormone thyroxine. Frog_sentence_445

This causes different tissues to develop in different ways. Frog_sentence_446

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. Frog_sentence_447

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. Frog_sentence_448

The nervous system becomes adapted for hearing and stereoscopic vision, and for new methods of locomotion and feeding. Frog_sentence_449

The eyes are repositioned higher up on the head and the eyelids and associated glands are formed. Frog_sentence_450

The eardrum, middle ear, and inner ear are developed. Frog_sentence_451

The skin becomes thicker and tougher, the lateral line system is lost, and skin glands are developed. Frog_sentence_452

The final stage is the disappearance of the tail, but this takes place rather later, the tissue being used to produce a spurt of growth in the limbs. Frog_sentence_453

Frogs are at their most vulnerable to predators when they are undergoing metamorphosis. Frog_sentence_454

At this time, the tail is being lost and locomotion by means of limbs is only just becoming established. Frog_sentence_455

Adults Frog_section_23

After metamorphosis, young adults may disperse into terrestrial habitats or continue to live in water. Frog_sentence_456

Almost all frog species are carnivorous as adults, preying on invertebrates, including arthropods, worms, snails, and slugs. Frog_sentence_457

A few of the larger ones may eat other frogs, small mammals, and fish. Frog_sentence_458

Some frogs use their sticky tongues to catch fast-moving prey, while others push food into their mouths with their hands. Frog_sentence_459

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 79.5% of its diet by volume. Frog_sentence_460

Adult frogs are themselves attacked by many predators. Frog_sentence_461

The northern leopard frog (Rana pipiens) is eaten by herons, hawks, fish, large salamanders, snakes, raccoons, skunks, mink, bullfrogs, and other animals. Frog_sentence_462

Frogs are primary predators and an important part of the food web. Frog_sentence_463

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. Frog_sentence_464

They are themselves eaten by secondary predators and are the primary terrestrial consumers of invertebrates, most of which feed on plants. Frog_sentence_465

By reducing herbivory, they play a part in increasing the growth of plants and are thus part of a delicately balanced ecosystem. Frog_sentence_466

Little is known about the longevity of frogs and toads in the wild, but some can live for many years. Frog_sentence_467

Skeletochronology is a method of examining bones to determine age. Frog_sentence_468

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. Frog_sentence_469

The oldest frogs had ten bands, so their age was believed to be 14 years, including the four-year tadpole stage. Frog_sentence_470

Captive frogs and toads have been recorded as living for up to 40 years, an age achieved by a European common toad (Bufo bufo). Frog_sentence_471

The cane toad (Bufo marinus) has been known to survive 24 years in captivity, and the American bullfrog (Rana catesbeiana) 14 years. Frog_sentence_472

Frogs from temperate climates hibernate during the winter, and four species are known to be able to withstand freezing during this time, including the wood frog (Rana sylvatica). Frog_sentence_473

Parental care Frog_section_24

Although care of offspring is poorly understood in frogs, up to an estimated 20% of amphibian species may care for their young in some way. Frog_sentence_474

The evolution of parental care in frogs is driven primarily by the size of the water body in which they breed. Frog_sentence_475

Those that breed in smaller water bodies tend to have greater and more complex parental care behaviour. Frog_sentence_476

Because predation of eggs and larvae is high in large water bodies, some frog species started to lay their eggs on land. Frog_sentence_477

Once this happened, the desiccating terrestrial environment demands that one or both parents keep them moist to ensure their survival. Frog_sentence_478

The subsequent need to transport hatched tadpoles to a water body required an even more intense form of parental care. Frog_sentence_479

In small pools, predators are mostly absent and competition between tadpoles becomes the variable that constrains their survival. Frog_sentence_480

Certain frog species avoid this competition by making use of smaller phytotelmata (water-filled leaf or small woody cavities) as sites for depositing a few tadpoles. Frog_sentence_481

While these smaller rearing sites are free from competition, they also lack sufficient nutrients to support a tadpole without parental assistance. Frog_sentence_482

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. Frog_sentence_483

The female strawberry poison-dart frog (Oophaga pumilio) lays her eggs on the forest floor. Frog_sentence_484

The male frog guards them from predation and carries water in his cloaca to keep them moist. Frog_sentence_485

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. Frog_sentence_486

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. Frog_sentence_487

The granular poison frog (Oophaga granulifera) looks after its tadpoles in a similar way. Frog_sentence_488

Many other diverse forms of parental care are seen in frogs. Frog_sentence_489

The tiny male Colostethus subpunctatus stands guard over his egg cluster, laid under a stone or log. Frog_sentence_490

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. Frog_sentence_491

He then moves on to another pool. Frog_sentence_492

The male common midwife toad (Alytes obstetricans) carries the eggs around with him attached to his hind legs. Frog_sentence_493

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. Frog_sentence_494

After three to six weeks, he travels to a pond and the eggs hatch into tadpoles. Frog_sentence_495

The tungara frog (Physalaemus pustulosus) builds a floating nest from foam to protect its eggs from predation. Frog_sentence_496

The foam is made from proteins and lectins, and seems to have antimicrobial properties. Frog_sentence_497

Several pairs of frogs may form a colonial nest on a previously built raft. Frog_sentence_498

The eggs are laid in the centre, followed by alternate layers of foam and eggs, finishing with a foam capping. Frog_sentence_499

Some frogs protect their offspring inside their own bodies. Frog_sentence_500

Both male and female pouched frogs (Assa darlingtoni) guard their eggs, which are laid on the ground. Frog_sentence_501

When the eggs hatch, the male lubricates his body with the jelly surrounding them and immerses himself in the egg mass. Frog_sentence_502

The tadpoles wriggle into skin pouches on his side, where they develop until they metamorphose into juvenile frogs. Frog_sentence_503

The female gastric-brooding frog (Rheobatrachus sp.) from Australia, now probably extinct, swallows her fertilized eggs, which then develop inside her stomach. Frog_sentence_504

She ceases to feed and stops secreting stomach acid. Frog_sentence_505

The tadpoles rely on the yolks of the eggs for nourishment. Frog_sentence_506

After six or seven weeks, they are ready for metamorphosis. Frog_sentence_507

The mother regurgitates the tiny frogs, which hop away from her mouth. Frog_sentence_508

The female Darwin's frog (Rhinoderma darwinii) from Chile lays up to 40 eggs on the ground, where they are guarded by the male. Frog_sentence_509

When the tadpoles are about to hatch, they are engulfed by the male, which carries them around inside his much-enlarged vocal sac. Frog_sentence_510

Here they are immersed in a frothy, viscous liquid that contains some nourishment to supplement what they obtain from the yolks of the eggs. Frog_sentence_511

They remain in the sac for seven to ten weeks before undergoing metamorphosis, after which they move into the male's mouth and emerge. Frog_sentence_512

Defence Frog_section_25

At first sight, frogs seem rather defenceless because of their small size, slow movement, thin skin, and lack of defensive structures, such as spines, claws or teeth. Frog_sentence_513

Many use camouflage to avoid detection, the skin often being spotted or streaked in neutral colours that allow a stationary frog to merge into its surroundings. Frog_sentence_514

Some can make prodigious leaps, often into water, that help them to evade potential attackers, while many have other defensive adaptations and strategies. Frog_sentence_515

The skin of many frogs contains mild toxic substances called bufotoxins to make them unpalatable to potential predators. Frog_sentence_516

Most toads and some frogs have large poison glands, the parotoid glands, located on the sides of their heads behind the eyes and other glands elsewhere on their bodies. Frog_sentence_517

These glands secrete mucus and a range of toxins that make frogs slippery to hold and distasteful or poisonous. Frog_sentence_518

If the noxious effect is immediate, the predator may cease its action and the frog may escape. Frog_sentence_519

If the effect develops more slowly, the predator may learn to avoid that species in future. Frog_sentence_520

Poisonous frogs tend to advertise their toxicity with bright colours, an adaptive strategy known as aposematism. Frog_sentence_521

The poison dart frogs in the family Dendrobatidae do this. Frog_sentence_522

They are typically red, orange, or yellow, often with contrasting black markings on their bodies. Frog_sentence_523

Allobates zaparo is not poisonous, but mimics the appearance of two different toxic species with which it shares a common range in an effort to deceive predators. Frog_sentence_524

Other species, such as the European fire-bellied toad (Bombina bombina), have their warning colour underneath. Frog_sentence_525

They "flash" this when attacked, adopting a pose that exposes the vivid colouring on their bellies. Frog_sentence_526

Some frogs, such as the poison dart frogs, are especially toxic. Frog_sentence_527

The native peoples of South America extract poison from these frogs to apply to their weapons for hunting, although few species are toxic enough to be used for this purpose. Frog_sentence_528

At least two non-poisonous frog species in tropical America (Eleutherodactylus gaigei and Lithodytes lineatus) mimic the colouration of dart poison frogs for self-protection. Frog_sentence_529

Some frogs obtain poisons from the ants and other arthropods they eat. Frog_sentence_530

Others, such as the Australian corroboree frogs (Pseudophryne corroboree and Pseudophryne pengilleyi), can synthesize the alkaloids themselves. Frog_sentence_531

The chemicals involved may be irritants, hallucinogens, convulsants, nerve poisons or vasoconstrictors. Frog_sentence_532

Many predators of frogs have become adapted to tolerate high levels of these poisons, but other creatures, including humans who handle the frogs, may be severely affected. Frog_sentence_533

Some frogs use bluff or deception. Frog_sentence_534

The European common toad (Bufo bufo) adopts a characteristic stance when attacked, inflating its body and standing with its hindquarters raised and its head lowered. Frog_sentence_535

The bullfrog (Rana catesbeiana) crouches down with eyes closed and head tipped forward when threatened. Frog_sentence_536

This places the parotoid glands in the most effective position, the other glands on its back begin to ooze noxious secretions and the most vulnerable parts of its body are protected. Frog_sentence_537

Another tactic used by some frogs is to "scream", the sudden loud noise tending to startle the predator. Frog_sentence_538

The gray tree frog (Hyla versicolor) makes an explosive sound that sometimes repels the shrew Blarina brevicauda. Frog_sentence_539

Although toads are avoided by many predators, the common garter snake (Thamnophis sirtalis) regularly feeds on them. Frog_sentence_540

The strategy employed by juvenile American toads (Bufo americanus) on being approached by a snake is to crouch down and remain immobile. Frog_sentence_541

This is usually successful, with the snake passing by and the toad remaining undetected. Frog_sentence_542

If it is encountered by the snake's head, however, the toad hops away before crouching defensively. Frog_sentence_543

Distribution Frog_section_26

Frogs live on all the continents except Antarctica, but they are not present on certain islands, especially those far away from continental land masses. Frog_sentence_544

Many species are isolated in restricted ranges by changes of climate or inhospitable territory, such as stretches of sea, mountain ridges, deserts, forest clearance, road construction, or other man-made barriers. Frog_sentence_545

Usually, a greater diversity of frogs occurs in tropical areas than in temperate regions, such as Europe. Frog_sentence_546

Some frogs inhabit arid areas, such as deserts, and rely on specific adaptations to survive. Frog_sentence_547

Members of the Australian genus Cyclorana bury themselves underground where they create a water-impervious cocoon in which to aestivate during dry periods. Frog_sentence_548

Once it rains, they emerge, find a temporary pool, and breed. Frog_sentence_549

Egg and tadpole development is very fast in comparison to those of most other frogs, so breeding can be completed before the pond dries up. Frog_sentence_550

Some frog species are adapted to a cold environment. Frog_sentence_551

The wood frog (Rana sylvatica), whose habitat extends into the Arctic Circle, buries itself in the ground during winter. Frog_sentence_552

Although much of its body freezes during this time, it maintains a high concentration of glucose in its vital organs, which protects them from damage. Frog_sentence_553

Conservation Frog_section_27

See also: Decline in amphibian populations Frog_sentence_554

In 2006, of 4,035 species of amphibians that depend on water during some lifecycle stage, 1,356 (33.6%) were considered to be threatened. Frog_sentence_555

This is likely to be an underestimate because it excludes 1,427 species for which evidence was insufficient to assess their status. Frog_sentence_556

Frog populations have declined dramatically since the 1950s. Frog_sentence_557

More than one-third of frog species are considered to be threatened with extinction, and more than 120 species are believed to have become extinct since the 1980s. Frog_sentence_558

Among these species are the gastric-brooding frogs of Australia and the golden toad of Costa Rica. Frog_sentence_559

The latter is of particular concern to scientists because it inhabited the pristine Monteverde Cloud Forest Reserve and its population crashed in 1987, along with about 20 other frog species in the area. Frog_sentence_560

This could not be linked directly to human activities, such as deforestation, and was outside the range of normal fluctuations in population size. Frog_sentence_561

Elsewhere, habitat loss is a significant cause of frog population decline, as are pollutants, climate change, increased UVB radiation, and the introduction of non-native predators and competitors. Frog_sentence_562

A Canadian study conducted in 2006 suggested heavy traffic in their environment was a larger threat to frog populations than was habitat loss. Frog_sentence_563

Emerging infectious diseases, including chytridiomycosis and ranavirus, are also devastating populations. Frog_sentence_564

Many environmental scientists believe amphibians, including frogs, are good biological indicators of broader ecosystem health because of their intermediate positions in food chains, their permeable skins, and typically biphasic lives (aquatic larvae and terrestrial adults). Frog_sentence_565

It appears that species with both aquatic eggs and larvae are most affected by the decline, while those with direct development are the most resistant. Frog_sentence_566

Frog mutations and genetic defects have increased since the 1990s. Frog_sentence_567

These often include missing legs or extra legs. Frog_sentence_568

Various causes have been identified or hypothesized, including an increase in ultraviolet radiation affecting the spawn on the surface of ponds, chemical contamination from pesticides and fertilizers, and parasites such as the trematode Ribeiroia ondatrae. Frog_sentence_569

Probably all these are involved in a complex way as stressors, environmental factors contributing to rates of disease, and vulnerability to attack by parasites. Frog_sentence_570

Malformations impair mobility and the individuals may not survive to adulthood. Frog_sentence_571

An increase in the number of frogs eaten by birds may actually increase the likelihood of parasitism of other frogs, because the trematode's complex lifecycle includes the ramshorn snail and several intermediate hosts such as birds. Frog_sentence_572

In a few cases, captive breeding programs have been established and have largely been successful. Frog_sentence_573

The World Association of Zoos and Aquariums named 2008 as the "Year of the Frog" in order to draw attention to the conservation issues faced by them. Frog_sentence_574

The cane toad (Bufo marinus) is a very adaptable species native to South and Central America. Frog_sentence_575

In the 1930s, it was introduced into Puerto Rico, and later various other islands in the Pacific and Caribbean region, as a biological pest control agent. Frog_sentence_576

In 1935, 3000 toads were liberated in the sugar cane fields of Queensland, Australia, in an attempt to control cane beetles such as Dermolepida albohirtum, the larvae of which damage and kill the canes. Frog_sentence_577

Initial results in many of these countries were positive, but it later became apparent that the toads upset the ecological balance in their new environments. Frog_sentence_578

They bred freely, competed with native frog species, ate bees and other harmless native invertebrates, had few predators in their adopted habitats, and poisoned pets, carnivorous birds, and mammals. Frog_sentence_579

In many of these countries, they are now regarded both as pests and invasive species, and scientists are looking for a biological method to control them. Frog_sentence_580

Uses Frog_section_28

Culinary Frog_section_29

Main article: Frog legs Frog_sentence_581

Frog legs are eaten by humans in many parts of the world. Frog_sentence_582

French cuisses de grenouille or frog legs dish is a traditional dish particularly served in the region of the Dombes (département of Ain). Frog_sentence_583

The dish is also common in French-speaking parts of Louisiana, particularly the Cajun areas of Southern Louisiana as well as New Orleans, United States. Frog_sentence_584

In Asia, frog legs are consumed in China, Vietnam, Thailand and Indonesia. Frog_sentence_585

Chinese edible frog and pig frogs are farmed and consumed on a large scale in some areas of China. Frog_sentence_586

Frog legs are part of Chinese Sichuan and Cantonese cuisine. Frog_sentence_587

In Indonesia, frog-leg soup is known as swikee or swike. Frog_sentence_588

Indonesia is the world's largest exporter of frog meat, exporting more than 5,000 tonnes of frog meat each year, mostly to France, Belgium and Luxembourg. Frog_sentence_589

Originally, they were supplied from local wild populations, but overexploitation led to a diminution in the supply. Frog_sentence_590

This resulted in the development of frog farming and a global trade in frogs. Frog_sentence_591

The main importing countries are France, Belgium, Luxembourg, and the United States, while the chief exporting nations are Indonesia and China. Frog_sentence_592

The annual global trade in the American bullfrog (Rana catesbeiana), mostly farmed in China, varies between 1200 and 2400 tonnes. Frog_sentence_593

The mountain chicken frog, so-called as it tastes of chicken, is now endangered, in part due to human consumption, and was a major food choice of the Dominicans. Frog_sentence_594

Coon, possum, partridges, prairie hen, and frogs were among the fare Mark Twain recorded as part of American cuisine. Frog_sentence_595

Scientific research Frog_section_30

See also: Animal testing on frogs Frog_sentence_596

Frogs are used for dissections in high school and university anatomy classes, often first being injected with coloured substances to enhance contrasts among the biological systems. Frog_sentence_597

This practice is declining due to animal welfare concerns, and "digital frogs" are now available for virtual dissection. Frog_sentence_598

Frogs have served as experimental animals throughout the history of science. Frog_sentence_599

Eighteenth-century biologist Luigi Galvani discovered the link between electricity and the nervous system by studying frogs. Frog_sentence_600

In 1852, H. F. Stannius used a frog's heart in a procedure called a Stannius ligature to demonstrate the ventricle and atria beat independently of each other and at different rates. Frog_sentence_601

The African clawed frog or platanna (Xenopus laevis) was first widely used in laboratories in pregnancy tests in the first half of the 20th century. Frog_sentence_602

A sample of urine from a pregnant woman injected into a female frog induces it to lay eggs, a discovery made by English zoologist Lancelot Hogben. Frog_sentence_603

This is because a hormone, human chorionic gonadotropin, is present in substantial quantities in the urine of women during pregnancy. Frog_sentence_604

In 1952, Robert Briggs and Thomas J. King cloned a frog by somatic cell nuclear transfer. Frog_sentence_605

This same technique was later used to create Dolly the sheep, and their experiment was the first time a successful nuclear transplantation had been accomplished in higher animals. Frog_sentence_606

Frogs are used in cloning research and other branches of embryology. Frog_sentence_607

Although alternative pregnancy tests have been developed, biologists continue to use Xenopus as a model organism in developmental biology because their embryos are large and easy to manipulate, they are readily obtainable, and can easily be kept in the laboratory. Frog_sentence_608

Xenopus laevis is increasingly being displaced by its smaller relative, Xenopus tropicalis, which reaches its reproductive age in five months rather than the one to two years for X. laevis, thus facilitating faster studies across generations. Frog_sentence_609

Genomes of Xenopus laevis, X. tropicalis, Rana catesbeiana, Rhinella marina, and Nanorana parkeri have been sequenced and deposited in the NCBI Genome database. Frog_sentence_610

As pets Frog_section_31

See also: Frogs in captivity Frog_sentence_611

Due to being inexpensive and relatively easy to care for, many species of frog and toad have become popular as exotic pets, they are undemanding and require low maintenance. Frog_sentence_612

Pharmaceutical Frog_section_32

Because frog toxins are extraordinarily diverse, they have raised the interest of biochemists as a "natural pharmacy". Frog_sentence_613

The alkaloid epibatidine, a painkiller 200 times more potent than morphine, is made by some species of poison dart frogs. Frog_sentence_614

Other chemicals isolated from the skins of frogs may offer resistance to HIV infection. Frog_sentence_615

Dart poisons are under active investigation for their potential as therapeutic drugs. Frog_sentence_616

It has long been suspected that pre-Columbian Mesoamericans used a toxic secretion produced by the cane toad as a hallucinogen, but more likely they used substances secreted by the Colorado River toad (Bufo alvarius). Frog_sentence_617

These contain bufotenin (5-MeO-DMT), a psychoactive compound that has been used in modern times as a recreational drug. Frog_sentence_618

Typically, the skin secretions are dried and then smoked. Frog_sentence_619

Illicit drug use by licking the skin of a toad has been reported in the media, but this may be an urban myth. Frog_sentence_620

Exudations from the skin of the golden poison frog (Phyllobates terribilis) are traditionally used by native Colombians to poison the darts they use for hunting. Frog_sentence_621

The tip of the projectile is rubbed over the back of the frog and the dart is launched from a blowgun. Frog_sentence_622

The combination of the two alkaloid toxins batrachotoxin and homobatrachotoxin is so powerful, one frog contains enough poison to kill an estimated 22,000 mice. Frog_sentence_623

Two other species, the Kokoe poison dart frog (Phyllobates aurotaenia) and the black-legged dart frog (Phyllobates bicolor) are also used for this purpose. Frog_sentence_624

These are less toxic and less abundant than the golden poison frog. Frog_sentence_625

They are impaled on pointed sticks and may be heated over a fire to maximise the quantity of poison that can be transferred to the dart. Frog_sentence_626

Cultural beliefs Frog_section_33

Main article: Frogs in culture Frog_sentence_627

Frogs feature prominently in folklore, fairy tales, and popular culture. Frog_sentence_628

They tend to be portrayed as benign, ugly, and clumsy, but with hidden talents. Frog_sentence_629

Examples include Michigan J. Frog, "The Frog Prince", and Kermit the Frog. Frog_sentence_630

The Warner Brothers cartoon One Froggy Evening features Michigan J. Frog, that will only dance and sing for the demolition worker who opens his time capsule, but will not perform in public. Frog_sentence_631

"The Frog Prince" is a fairy tale about a frog that turns into a handsome prince after he has rescued a princess's golden ball and she has taken him into her palace. Frog_sentence_632

Kermit the Frog is a conscientious and disciplined character from The Muppet Show and Sesame Street; while openly friendly and greatly talented, he is often portrayed as cringing at the fanciful behavior of more flamboyant characters. Frog_sentence_633

The Moche people of ancient Peru worshipped animals, and often depicted frogs in their art. Frog_sentence_634

In Panama, local legend held that good fortune would come to anyone who spotted a Panamanian golden frog. Frog_sentence_635

Some believed when one of these frogs died, it would turn into a golden talisman known as a huaca. Frog_sentence_636

Today, despite being extinct in the wild, Panamanian golden frogs remain an important cultural symbol and are illustrated on decorative cloth molas made by the Kuna people. Frog_sentence_637

They also appear as part of the inlaid design on a new overpass in Panama City, on T-shirts, and even on lottery tickets. Frog_sentence_638

See also Frog_section_34

Frog_unordered_list_7


Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Frog.