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For other uses, see Amphibian (disambiguation). Amphibian_sentence_0

"Amphibia" redirects here. Amphibian_sentence_1

For the TV series, see Amphibia (TV series). Amphibian_sentence_2



Temporal range: Late Devonianpresent, 370–0 Ma PreꞒ O S D C P T J K Pg NAmphibian_header_cell_0_0_0

Scientific classification AmphibiaAmphibian_header_cell_0_1_0
Kingdom:Amphibian_cell_0_2_0 AnimaliaAmphibian_cell_0_2_1
Phylum:Amphibian_cell_0_3_0 ChordataAmphibian_cell_0_3_1
Clade:Amphibian_cell_0_4_0 BatrachomorphaAmphibian_cell_0_4_1
Class:Amphibian_cell_0_5_0 Amphibia

Gray 1825Amphibian_cell_0_5_1


Amphibians are ectothermic, tetrapod vertebrates of the class Amphibia. Amphibian_sentence_3

All living amphibians belong to the group Lissamphibia. Amphibian_sentence_4

They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arboreal or freshwater aquatic ecosystems. Amphibian_sentence_5

Thus amphibians typically start out as larvae living in water, but some species have developed behavioural adaptations to bypass this. Amphibian_sentence_6

The young generally undergo metamorphosis from larva with gills to an adult air-breathing form with lungs. Amphibian_sentence_7

Amphibians use their skin as a secondary respiratory surface and some small terrestrial salamanders and frogs lack lungs and rely entirely on their skin. Amphibian_sentence_8

They are superficially similar to lizards but, along with mammals and birds, reptiles are amniotes and do not require water bodies in which to breed. Amphibian_sentence_9

With their complex reproductive needs and permeable skins, amphibians are often ecological indicators; in recent decades there has been a dramatic decline in amphibian populations for many species around the globe. Amphibian_sentence_10

The earliest amphibians evolved in the Devonian period from sarcopterygian fish with lungs and bony-limbed fins, features that were helpful in adapting to dry land. Amphibian_sentence_11

They diversified and became dominant during the Carboniferous and Permian periods, but were later displaced by reptiles and other vertebrates. Amphibian_sentence_12

Over time, amphibians shrank in size and decreased in diversity, leaving only the modern subclass Lissamphibia. Amphibian_sentence_13

The three modern orders of amphibians are Anura (the frogs and toads), Urodela (the salamanders), and Apoda (the caecilians). Amphibian_sentence_14

The number of known amphibian species is approximately 8,000, of which nearly 90% are frogs. Amphibian_sentence_15

The smallest amphibian (and vertebrate) in the world is a frog from New Guinea (Paedophryne amauensis) with a length of just 7.7 mm (0.30 in). Amphibian_sentence_16

The largest living amphibian is the 1.8 m (5 ft 11 in) South China giant salamander (Andrias sligoi), but this is dwarfed by the extinct 9 m (30 ft) Prionosuchus from the middle Permian of Brazil. Amphibian_sentence_17

The study of amphibians is called batrachology, while the study of both reptiles and amphibians is called herpetology. Amphibian_sentence_18

Classification Amphibian_section_0

See also: List of amphibians Amphibian_sentence_19

The word "amphibian" is derived from the Ancient Greek term ἀμφίβιος (amphíbios), which means "both kinds of life", ἀμφί meaning "of both kinds" and βιος meaning "life". Amphibian_sentence_20

The term was initially used as a general adjective for animals that could live on land or in water, including seals and otters. Amphibian_sentence_21

Traditionally, the class Amphibia includes all tetrapod vertebrates that are not amniotes. Amphibian_sentence_22

Amphibia in its widest sense (sensu lato) was divided into three subclasses, two of which are extinct: Amphibian_sentence_23


  • Subclass Lepospondyli† (small Paleozoic group, which are more closely related to amniotes than Lissamphibia)Amphibian_item_0_0
  • Subclass Temnospondyli† (diverse Paleozoic and early Mesozoic grade)Amphibian_item_0_1
  • Subclass Lissamphibia (all modern amphibians, including frogs, toads, salamanders, newts and caecilians)Amphibian_item_0_2
    • Salientia (frogs, toads and relatives): Jurassic to present—6,200 current species in 53 familiesAmphibian_item_0_3
    • Caudata (salamanders, newts and relatives): Jurassic to present—652 current species in 9 familiesAmphibian_item_0_4
    • Gymnophiona (caecilians and relatives): Jurassic to present—192 current species in 10 familiesAmphibian_item_0_5
    • Allocaudata† (Albanerpetontidae) Middle Jurassic - Early PleistoceneAmphibian_item_0_6

The actual number of species in each group depends on the taxonomic classification followed. Amphibian_sentence_24

The two most common systems are the classification adopted by the website AmphibiaWeb, University of California, Berkeley and the classification by herpetologist Darrel Frost and the American Museum of Natural History, available as the online reference database "Amphibian Species of the World". Amphibian_sentence_25

The numbers of species cited above follows Frost and the total number of known amphibian species as of March 31, 2019 is exactly 8,000, of which nearly 90% are frogs. Amphibian_sentence_26

With the phylogenetic classification, the taxon Labyrinthodontia has been discarded as it is a polyparaphyletic group without unique defining features apart from shared primitive characteristics. Amphibian_sentence_27

Classification varies according to the preferred phylogeny of the author and whether they use a stem-based or a node-based classification. Amphibian_sentence_28

Traditionally, amphibians as a class are defined as all tetrapods with a larval stage, while the group that includes the common ancestors of all living amphibians (frogs, salamanders and caecilians) and all their descendants is called Lissamphibia. Amphibian_sentence_29

The phylogeny of Paleozoic amphibians is uncertain, and Lissamphibia may possibly fall within extinct groups, like the Temnospondyli (traditionally placed in the subclass Labyrinthodontia) or the Lepospondyli, and in some analyses even in the amniotes. Amphibian_sentence_30

This means that advocates of phylogenetic nomenclature have removed a large number of basal Devonian and Carboniferous amphibian-type tetrapod groups that were formerly placed in Amphibia in Linnaean taxonomy, and included them elsewhere under cladistic taxonomy. Amphibian_sentence_31

If the common ancestor of amphibians and amniotes is included in Amphibia, it becomes a paraphyletic group. Amphibian_sentence_32

All modern amphibians are included in the subclass Lissamphibia, which is usually considered a clade, a group of species that have evolved from a common ancestor. Amphibian_sentence_33

The three modern orders are Anura (the frogs and toads), Caudata (or Urodela, the salamanders), and Gymnophiona (or Apoda, the caecilians). Amphibian_sentence_34

It has been suggested that salamanders arose separately from a Temnospondyl-like ancestor, and even that caecilians are the sister group of the advanced reptiliomorph amphibians, and thus of amniotes. Amphibian_sentence_35

Although the fossils of several older proto-frogs with primitive characteristics are known, the oldest "true frog" is Prosalirus bitis, from the Early Jurassic Kayenta Formation of Arizona. Amphibian_sentence_36

It is anatomically very similar to modern frogs. Amphibian_sentence_37

The oldest known caecilian is another Early Jurassic species, Eocaecilia micropodia, also from Arizona. Amphibian_sentence_38

The earliest salamander is Beiyanerpeton jianpingensis from the Late Jurassic of northeastern China. Amphibian_sentence_39

Authorities disagree as to whether Salientia is a superorder that includes the order Anura, or whether Anura is a sub-order of the order Salientia. Amphibian_sentence_40

The Lissamphibia are traditionally divided into three orders, but an extinct salamander-like family, the Albanerpetontidae, is now considered part of Lissamphibia alongside the superorder Salientia. Amphibian_sentence_41

Furthermore, Salientia includes all three recent orders plus the Triassic proto-frog, Triadobatrachus. Amphibian_sentence_42

Evolutionary history Amphibian_section_1

Main article: Evolution of tetrapods Amphibian_sentence_43

See also: List of prehistoric amphibians Amphibian_sentence_44

The first major groups of amphibians developed in the Devonian period, around 370 million years ago, from lobe-finned fish which were similar to the modern coelacanth and lungfish. Amphibian_sentence_45

These ancient lobe-finned fish had evolved multi-jointed leg-like fins with digits that enabled them to crawl along the sea bottom. Amphibian_sentence_46

Some fish had developed primitive lungs that help them breathe air when the stagnant pools of the Devonian swamps were low in oxygen. Amphibian_sentence_47

They could also use their strong fins to hoist themselves out of the water and onto dry land if circumstances so required. Amphibian_sentence_48

Eventually, their bony fins would evolve into limbs and they would become the ancestors to all tetrapods, including modern amphibians, reptiles, birds, and mammals. Amphibian_sentence_49

Despite being able to crawl on land, many of these prehistoric tetrapodomorph fish still spent most of their time in the water. Amphibian_sentence_50

They had started to develop lungs, but still breathed predominantly with gills. Amphibian_sentence_51

Many examples of species showing transitional features have been discovered. Amphibian_sentence_52

Ichthyostega was one of the first primitive amphibians, with nostrils and more efficient lungs. Amphibian_sentence_53

It had four sturdy limbs, a neck, a tail with fins and a skull very similar to that of the lobe-finned fish, Eusthenopteron. Amphibian_sentence_54

Amphibians evolved adaptations that allowed them to stay out of the water for longer periods. Amphibian_sentence_55

Their lungs improved and their skeletons became heavier and stronger, better able to support the weight of their bodies on land. Amphibian_sentence_56

They developed "hands" and "feet" with five or more digits; the skin became more capable of retaining body fluids and resisting desiccation. Amphibian_sentence_57

The fish's hyomandibula bone in the hyoid region behind the gills diminished in size and became the stapes of the amphibian ear, an adaptation necessary for hearing on dry land. Amphibian_sentence_58

An affinity between the amphibians and the teleost fish is the multi-folded structure of the teeth and the paired supra-occipital bones at the back of the head, neither of these features being found elsewhere in the animal kingdom. Amphibian_sentence_59

At the end of the Devonian period (360 million years ago), the seas, rivers and lakes were teeming with life while the land was the realm of early plants and devoid of vertebrates, though some, such as Ichthyostega, may have sometimes hauled themselves out of the water. Amphibian_sentence_60

It is thought they may have propelled themselves with their forelimbs, dragging their hindquarters in a similar manner to that used by the elephant seal. Amphibian_sentence_61

In the early Carboniferous (360 to 345 million years ago), the climate became wet and warm. Amphibian_sentence_62

Extensive swamps developed with mosses, ferns, horsetails and calamites. Amphibian_sentence_63

Air-breathing arthropods evolved and invaded the land where they provided food for the carnivorous amphibians that began to adapt to the terrestrial environment. Amphibian_sentence_64

There were no other tetrapods on the land and the amphibians were at the top of the food chain, occupying the ecological position currently held by the crocodile. Amphibian_sentence_65

Though equipped with limbs and the ability to breathe air, most still had a long tapering body and strong tail. Amphibian_sentence_66

They were the top land predators, sometimes reaching several metres in length, preying on the large insects of the period and the many types of fish in the water. Amphibian_sentence_67

They still needed to return to water to lay their shell-less eggs, and even most modern amphibians have a fully aquatic larval stage with gills like their fish ancestors. Amphibian_sentence_68

It was the development of the amniotic egg, which prevents the developing embryo from drying out, that enabled the reptiles to reproduce on land and which led to their dominance in the period that followed. Amphibian_sentence_69

After the Carboniferous rainforest collapse amphibian dominance gave way to reptiles, and amphibians were further devastated by the Permian–Triassic extinction event. Amphibian_sentence_70

During the Triassic Period (250 to 200 million years ago), the reptiles continued to out-compete the amphibians, leading to a reduction in both the amphibians' size and their importance in the biosphere. Amphibian_sentence_71

According to the fossil record, Lissamphibia, which includes all modern amphibians and is the only surviving lineage, may have branched off from the extinct groups Temnospondyli and Lepospondyli at some period between the Late Carboniferous and the Early Triassic. Amphibian_sentence_72

The relative scarcity of fossil evidence precludes precise dating, but the most recent molecular study, based on multilocus sequence typing, suggests a Late Carboniferous/Early Permian origin for extant amphibians. Amphibian_sentence_73

The origins and evolutionary relationships between the three main groups of amphibians is a matter of debate. Amphibian_sentence_74

A 2005 molecular phylogeny, based on rDNA analysis, suggests that salamanders and caecilians are more closely related to each other than they are to frogs. Amphibian_sentence_75

It also appears that the divergence of the three groups took place in the Paleozoic or early Mesozoic (around 250 million years ago), before the breakup of the supercontinent Pangaea and soon after their divergence from the lobe-finned fish. Amphibian_sentence_76

The briefness of this period, and the swiftness with which radiation took place, would help account for the relative scarcity of primitive amphibian fossils. Amphibian_sentence_77

There are large gaps in the fossil record, but the discovery of a Gerobatrachus hottoni from the Early Permian in Texas in 2008 provided a missing link with many of the characteristics of modern frogs. Amphibian_sentence_78

Molecular analysis suggests that the frog–salamander divergence took place considerably earlier than the palaeontological evidence indicates. Amphibian_sentence_79

Newer research indicates that the common ancestor of all Lissamphibians lived about 315 million years ago, and that stereospondyls are the closest relatives to the caecilians. Amphibian_sentence_80

As they evolved from lunged fish, amphibians had to make certain adaptations for living on land, including the need to develop new means of locomotion. Amphibian_sentence_81

In the water, the sideways thrusts of their tails had propelled them forward, but on land, quite different mechanisms were required. Amphibian_sentence_82

Their vertebral columns, limbs, limb girdles and musculature needed to be strong enough to raise them off the ground for locomotion and feeding. Amphibian_sentence_83

Terrestrial adults discarded their lateral line systems and adapted their sensory systems to receive stimuli via the medium of the air. Amphibian_sentence_84

They needed to develop new methods to regulate their body heat to cope with fluctuations in ambient temperature. Amphibian_sentence_85

They developed behaviours suitable for reproduction in a terrestrial environment. Amphibian_sentence_86

Their skins were exposed to harmful ultraviolet rays that had previously been absorbed by the water. Amphibian_sentence_87

The skin changed to become more protective and prevent excessive water loss. Amphibian_sentence_88

Characteristics Amphibian_section_2

The superclass Tetrapoda is divided into four classes of vertebrate animals with four limbs. Amphibian_sentence_89

Reptiles, birds and mammals are amniotes, the eggs of which are either laid or carried by the female and are surrounded by several membranes, some of which are impervious. Amphibian_sentence_90

Lacking these membranes, amphibians require water bodies for reproduction, although some species have developed various strategies for protecting or bypassing the vulnerable aquatic larval stage. Amphibian_sentence_91

They are not found in the sea with the exception of one or two frogs that live in brackish water in mangrove swamps; the Anderson's salamander meanwhile occurs in brackish or salt water lakes. Amphibian_sentence_92

On land, amphibians are restricted to moist habitats because of the need to keep their skin damp. Amphibian_sentence_93

Modern amphibians have a simplified anatomy compared to their ancestors due to paedomorphosis, caused by two evolutionary trends: miniaturization and an unusually large genome, which result in a slower growth and development rate compared to other vertebrates. Amphibian_sentence_94

Another reason for their size is associated with their rapid metamorphosis, which seems to have evolved only in the ancestors of lissamphibia; in all other known lines the development was much more gradual. Amphibian_sentence_95

Because a remodeling of the feeding apparatus means they don't eat during the metamorphosis, the metamorphosis has to go faster the smaller the individual is, so it happens at an early stage when the larvae are still small. Amphibian_sentence_96

(The largest species of salamanders don't go through a metamorphosis.) Amphibian_sentence_97

Amphibians that lay eggs on land often go through the whole metamorphosis inside the egg. Amphibian_sentence_98

An anamniotic terrestrial egg is less than 1 cm in diameter due to diffusion problems, a size which puts a limit on the amount of posthatching growth. Amphibian_sentence_99

The smallest amphibian (and vertebrate) in the world is a microhylid frog from New Guinea (Paedophryne amauensis) first discovered in 2012. Amphibian_sentence_100

It has an average length of 7.7 mm (0.30 in) and is part of a genus that contains four of the world's ten smallest frog species. Amphibian_sentence_101

The largest living amphibian is the 1.8 m (5 ft 11 in) Chinese giant salamander (Andrias davidianus) but this is a great deal smaller than the largest amphibian that ever existed—the extinct 9 m (30 ft) Prionosuchus, a crocodile-like temnospondyl dating to 270 million years ago from the middle Permian of Brazil. Amphibian_sentence_102

The largest frog is the African Goliath frog (Conraua goliath), which can reach 32 cm (13 in) and weigh 3 kg (6.6 lb). Amphibian_sentence_103

Amphibians are ectothermic (cold-blooded) vertebrates that do not maintain their body temperature through internal physiological processes. Amphibian_sentence_104

Their metabolic rate is low and as a result, their food and energy requirements are limited. Amphibian_sentence_105

In the adult state, they have tear ducts and movable eyelids, and most species have ears that can detect airborne or ground vibrations. Amphibian_sentence_106

They have muscular tongues, which in many species can be protruded. Amphibian_sentence_107

Modern amphibians have fully ossified vertebrae with articular processes. Amphibian_sentence_108

Their ribs are usually short and may be fused to the vertebrae. Amphibian_sentence_109

Their skulls are mostly broad and short, and are often incompletely ossified. Amphibian_sentence_110

Their skin contains little keratin and lacks scales, apart from a few fish-like scales in certain caecilians. Amphibian_sentence_111

The skin contains many mucous glands and in some species, poison glands (a type of granular gland). Amphibian_sentence_112

The hearts of amphibians have three chambers, two atria and one ventricle. Amphibian_sentence_113

They have a urinary bladder and nitrogenous waste products are excreted primarily as urea. Amphibian_sentence_114

Most amphibians lay their eggs in water and have aquatic larvae that undergo metamorphosis to become terrestrial adults. Amphibian_sentence_115

Amphibians breathe by means of a pump action in which air is first drawn into the buccopharyngeal region through the nostrils. Amphibian_sentence_116

These are then closed and the air is forced into the lungs by contraction of the throat. Amphibian_sentence_117

They supplement this with gas exchange through the skin. Amphibian_sentence_118

Anura Amphibian_section_3

The order Anura (from the Ancient Greek a(n)- meaning "without" and oura meaning "tail") comprises the frogs and toads. Amphibian_sentence_119

They usually have long hind limbs that fold underneath them, shorter forelimbs, webbed toes with no claws, no tails, large eyes and glandular moist skin. Amphibian_sentence_120

Members of this order with smooth skins are commonly referred to as frogs, while those with skins are known as toads. Amphibian_sentence_121

The difference is not a formal one taxonomically and there are numerous exceptions to this rule. Amphibian_sentence_122

Members of the family Bufonidae are known as the "true toads". Amphibian_sentence_123

Frogs range in size from the 30-centimetre (12 in) Goliath frog (Conraua goliath) of West Africa to the 7.7-millimetre (0.30 in) Paedophryne amauensis, first described in Papua New Guinea in 2012, which is also the smallest known vertebrate. Amphibian_sentence_124

Although most species are associated with water and damp habitats, some are specialised to live in trees or in deserts. Amphibian_sentence_125

They are found worldwide except for polar areas. Amphibian_sentence_126

Anura is divided into three suborders that are broadly accepted by the scientific community, but the relationships between some families remain unclear. Amphibian_sentence_127

Future molecular studies should provide further insights into their evolutionary relationships. Amphibian_sentence_128

The suborder Archaeobatrachia contains four families of primitive frogs. Amphibian_sentence_129

These are Ascaphidae, Bombinatoridae, Discoglossidae and Leiopelmatidae which have few derived features and are probably paraphyletic with regard to other frog lineages. Amphibian_sentence_130

The six families in the more evolutionarily advanced suborder Mesobatrachia are the fossorial Megophryidae, Pelobatidae, Pelodytidae, Scaphiopodidae and Rhinophrynidae and the obligatorily aquatic Pipidae. Amphibian_sentence_131

These have certain characteristics that are intermediate between the two other suborders. Amphibian_sentence_132

Neobatrachia is by far the largest suborder and includes the remaining families of modern frogs, including most common species. Amphibian_sentence_133

Ninety-six percent of the over 5,000 extant species of frog are neobatrachians. Amphibian_sentence_134

Caudata Amphibian_section_4

The order Caudata (from the Latin cauda meaning "tail") consists of the salamanders—elongated, low-slung animals that mostly resemble lizards in form. Amphibian_sentence_135

This is a symplesiomorphic trait and they are no more closely related to lizards than they are to mammals. Amphibian_sentence_136

Salamanders lack claws, have scale-free skins, either smooth or covered with tubercles, and tails that are usually flattened from side to side and often finned. Amphibian_sentence_137

They range in size from the Chinese giant salamander (Andrias davidianus), which has been reported to grow to a length of 1.8 metres (5 ft 11 in), to the diminutive Thorius pennatulus from Mexico which seldom exceeds 20 mm (0.8 in) in length. Amphibian_sentence_138

Salamanders have a mostly Laurasian distribution, being present in much of the Holarctic region of the northern hemisphere. Amphibian_sentence_139

The family Plethodontidae is also found in Central America and South America north of the Amazon basin; South America was apparently invaded from Central America by about the start of the Miocene, 23 million years ago. Amphibian_sentence_140

Urodela is a name sometimes used for all the extant species of salamanders. Amphibian_sentence_141

Members of several salamander families have become paedomorphic and either fail to complete their metamorphosis or retain some larval characteristics as adults. Amphibian_sentence_142

Most salamanders are under 15 cm (6 in) long. Amphibian_sentence_143

They may be terrestrial or aquatic and many spend part of the year in each habitat. Amphibian_sentence_144

When on land, they mostly spend the day hidden under stones or logs or in dense vegetation, emerging in the evening and night to forage for worms, insects and other invertebrates. Amphibian_sentence_145

The suborder Cryptobranchoidea contains the primitive salamanders. Amphibian_sentence_146

A number of fossil cryptobranchids have been found, but there are only three living species, the Chinese giant salamander (Andrias davidianus), the Japanese giant salamander (Andrias japonicus) and the hellbender (Cryptobranchus alleganiensis) from North America. Amphibian_sentence_147

These large amphibians retain several larval characteristics in their adult state; gills slits are present and the eyes are unlidded. Amphibian_sentence_148

A unique feature is their ability to feed by suction, depressing either the left side of their lower jaw or the right. Amphibian_sentence_149

The males excavate nests, persuade females to lay their egg strings inside them, and guard them. Amphibian_sentence_150

As well as breathing with lungs, they respire through the many folds in their thin skin, which has capillaries close to the surface. Amphibian_sentence_151

The suborder Salamandroidea contains the advanced salamanders. Amphibian_sentence_152

They differ from the cryptobranchids by having fused prearticular bones in the lower jaw, and by using internal fertilisation. Amphibian_sentence_153

In salamandrids, the male deposits a bundle of sperm, the spermatophore, and the female picks it up and inserts it into her cloaca where the sperm is stored until the eggs are laid. Amphibian_sentence_154

The largest family in this group is Plethodontidae, the lungless salamanders, which includes 60% of all salamander species. Amphibian_sentence_155

The family Salamandridae includes the true salamanders and the name "newt" is given to members of its subfamily Pleurodelinae. Amphibian_sentence_156

The third suborder, Sirenoidea, contains the four species of sirens, which are in a single family, Sirenidae. Amphibian_sentence_157

Members of this order are eel-like aquatic salamanders with much reduced forelimbs and no hind limbs. Amphibian_sentence_158

Some of their features are primitive while others are derived. Amphibian_sentence_159

Fertilisation is likely to be external as sirenids lack the cloacal glands used by male salamandrids to produce spermatophores and the females lack spermathecae for sperm storage. Amphibian_sentence_160

Despite this, the eggs are laid singly, a behaviour not conducive for external fertilisation. Amphibian_sentence_161

Gymnophiona Amphibian_section_5

The order Gymnophiona (from the Greek gymnos meaning "naked" and ophis meaning "serpent") or Apoda comprises the caecilians. Amphibian_sentence_162

These are long, cylindrical, limbless animals with a snake- or worm-like form. Amphibian_sentence_163

The adults vary in length from 8 to 75 centimetres (3 to 30 inches) with the exception of Thomson's caecilian (Caecilia thompsoni), which can reach 150 centimetres (4.9 feet). Amphibian_sentence_164

A caecilian's skin has a large number of transverse folds and in some species contains tiny embedded dermal scales. Amphibian_sentence_165

It has rudimentary eyes covered in skin, which are probably limited to discerning differences in light intensity. Amphibian_sentence_166

It also has a pair of short tentacles near the eye that can be extended and which have tactile and olfactory functions. Amphibian_sentence_167

Most caecilians live underground in burrows in damp soil, in rotten wood and under plant debris, but some are aquatic. Amphibian_sentence_168

Most species lay their eggs underground and when the larvae hatch, they make their way to adjacent bodies of water. Amphibian_sentence_169

Others brood their eggs and the larvae undergo metamorphosis before the eggs hatch. Amphibian_sentence_170

A few species give birth to live young, nourishing them with glandular secretions while they are in the oviduct. Amphibian_sentence_171

Caecilians have a mostly Gondwanan distribution, being found in tropical regions of Africa, Asia and Central and South America. Amphibian_sentence_172

Anatomy and physiology Amphibian_section_6

Skin Amphibian_section_7

The structure contains some typical characteristics common to terrestrial vertebrates, such as the presence of highly cornified outer layers, renewed periodically through a moulting process controlled by the pituitary and thyroid glands. Amphibian_sentence_173

Local thickenings (often called warts) are common, such as those found on toads. Amphibian_sentence_174

The outside of the skin is shed periodically mostly in one piece, in contrast to mammals and birds where it is shed in flakes. Amphibian_sentence_175

Amphibians often eat the sloughed skin. Amphibian_sentence_176

Caecilians are unique among amphibians in having mineralized dermal scales embedded in the dermis between the furrows in the skin. Amphibian_sentence_177

The similarity of these to the scales of bony fish is largely superficial. Amphibian_sentence_178

Lizards and some frogs have somewhat similar osteoderms forming bony deposits in the dermis, but this is an example of convergent evolution with similar structures having arisen independently in diverse vertebrate lineages. Amphibian_sentence_179

Amphibian skin is permeable to water. Amphibian_sentence_180

Gas exchange can take place through the skin (cutaneous respiration) and this allows adult amphibians to respire without rising to the surface of water and to hibernate at the bottom of ponds. Amphibian_sentence_181

To compensate for their thin and delicate skin, amphibians have evolved mucous glands, principally on their heads, backs and tails. Amphibian_sentence_182

The secretions produced by these help keep the skin moist. Amphibian_sentence_183

In addition, most species of amphibian have granular glands that secrete distasteful or poisonous substances. Amphibian_sentence_184

Some amphibian toxins can be lethal to humans while others have little effect. Amphibian_sentence_185

The main poison-producing glands, the parotoids, produce the neurotoxin bufotoxin and are located behind the ears of toads, along the backs of frogs, behind the eyes of salamanders and on the upper surface of caecilians. Amphibian_sentence_186

The skin colour of amphibians is produced by three layers of pigment cells called chromatophores. Amphibian_sentence_187

These three cell layers consist of the melanophores (occupying the deepest layer), the guanophores (forming an intermediate layer and containing many granules, producing a blue-green colour) and the lipophores (yellow, the most superficial layer). Amphibian_sentence_188

The colour change displayed by many species is initiated by hormones secreted by the pituitary gland. Amphibian_sentence_189

Unlike bony fish, there is no direct control of the pigment cells by the nervous system, and this results in the colour change taking place more slowly than happens in fish. Amphibian_sentence_190

A vividly coloured skin usually indicates that the species is toxic and is a warning sign to predators. Amphibian_sentence_191

Skeletal system and locomotion Amphibian_section_8

Amphibians have a skeletal system that is structurally homologous to other tetrapods, though with a number of variations. Amphibian_sentence_192

They all have four limbs except for the legless caecilians and a few species of salamander with reduced or no limbs. Amphibian_sentence_193

The bones are hollow and lightweight. Amphibian_sentence_194

The musculoskeletal system is strong to enable it to support the head and body. Amphibian_sentence_195

The bones are fully ossified and the vertebrae interlock with each other by means of overlapping processes. Amphibian_sentence_196

The pectoral girdle is supported by muscle, and the well-developed pelvic girdle is attached to the backbone by a pair of sacral ribs. Amphibian_sentence_197

The ilium slopes forward and the body is held closer to the ground than is the case in mammals. Amphibian_sentence_198

In most amphibians, there are four digits on the fore foot and five on the hind foot, but no claws on either. Amphibian_sentence_199

Some salamanders have fewer digits and the amphiumas are eel-like in appearance with tiny, stubby legs. Amphibian_sentence_200

The sirens are aquatic salamanders with stumpy forelimbs and no hind limbs. Amphibian_sentence_201

The caecilians are limbless. Amphibian_sentence_202

They burrow in the manner of earthworms with zones of muscle contractions moving along the body. Amphibian_sentence_203

On the surface of the ground or in water they move by undulating their body from side to side. Amphibian_sentence_204

In frogs, the hind legs are larger than the fore legs, especially so in those species that principally move by jumping or swimming. Amphibian_sentence_205

In the walkers and runners the hind limbs are not so large, and the burrowers mostly have short limbs and broad bodies. Amphibian_sentence_206

The feet have adaptations for the way of life, with webbing between the toes for swimming, broad adhesive toe pads for climbing, and keratinised tubercles on the hind feet for digging (frogs usually dig backwards into the soil). Amphibian_sentence_207

In most salamanders, the limbs are short and more or less the same length and project at right angles from the body. Amphibian_sentence_208

Locomotion on land is by walking and the tail often swings from side to side or is used as a prop, particularly when climbing. Amphibian_sentence_209

In their normal gait, only one leg is advanced at a time in the manner adopted by their ancestors, the lobe-finned fish. Amphibian_sentence_210

Some salamanders in the genus Aneides and certain plethodontids climb trees and have long limbs, large toepads and prehensile tails. Amphibian_sentence_211

In aquatic salamanders and in frog tadpoles, the tail has dorsal and ventral fins and is moved from side to side as a means of propulsion. Amphibian_sentence_212

Adult frogs do not have tails and caecilians have only very short ones. Amphibian_sentence_213

Salamanders use their tails in defence and some are prepared to jettison them to save their lives in a process known as autotomy. Amphibian_sentence_214

Certain species in the Plethodontidae have a weak zone at the base of the tail and use this strategy readily. Amphibian_sentence_215

The tail often continues to twitch after separation which may distract the attacker and allow the salamander to escape. Amphibian_sentence_216

Both tails and limbs can be regenerated. Amphibian_sentence_217

Adult frogs are unable to regrow limbs but tadpoles can do so. Amphibian_sentence_218

Circulatory system Amphibian_section_9

Amphibians have a juvenile stage and an adult stage, and the circulatory systems of the two are distinct. Amphibian_sentence_219

In the juvenile (or tadpole) stage, the circulation is similar to that of a fish; the two-chambered heart pumps the blood through the gills where it is oxygenated, and is spread around the body and back to the heart in a single loop. Amphibian_sentence_220

In the adult stage, amphibians (especially frogs) lose their gills and develop lungs. Amphibian_sentence_221

They have a heart that consists of a single ventricle and two atria. Amphibian_sentence_222

When the ventricle starts contracting, deoxygenated blood is pumped through the pulmonary artery to the lungs. Amphibian_sentence_223

Continued contraction then pumps oxygenated blood around the rest of the body. Amphibian_sentence_224

Mixing of the two bloodstreams is minimized by the anatomy of the chambers. Amphibian_sentence_225

Nervous and sensory systems Amphibian_section_10

The nervous system is basically the same as in other vertebrates, with a central brain, a spinal cord, and nerves throughout the body. Amphibian_sentence_226

The amphibian brain is less well developed than that of reptiles, birds and mammals but is similar in morphology and function to that of a fish. Amphibian_sentence_227

It is believed amphibians are capable of perceiving pain. Amphibian_sentence_228

The brain consists of equal parts, cerebrum, midbrain and cerebellum. Amphibian_sentence_229

Various parts of the cerebrum process sensory input, such as smell in the olfactory lobe and sight in the optic lobe, and it is additionally the centre of behaviour and learning. Amphibian_sentence_230

The cerebellum is the center of muscular coordination and the medulla oblongata controls some organ functions including heartbeat and respiration. Amphibian_sentence_231

The brain sends signals through the spinal cord and nerves to regulate activity in the rest of the body. Amphibian_sentence_232

The pineal body, known to regulate sleep patterns in humans, is thought to produce the hormones involved in hibernation and aestivation in amphibians. Amphibian_sentence_233

Tadpoles retain the lateral line system of their ancestral fishes, but this is lost in terrestrial adult amphibians. Amphibian_sentence_234

Some caecilians possess electroreceptors that allow them to locate objects around them when submerged in water. Amphibian_sentence_235

The ears are well developed in frogs. Amphibian_sentence_236

There is no external ear, but the large circular eardrum lies on the surface of the head just behind the eye. Amphibian_sentence_237

This vibrates and sound is transmitted through a single bone, the stapes, to the inner ear. Amphibian_sentence_238

Only high-frequency sounds like mating calls are heard in this way, but low-frequency noises can be detected through another mechanism. Amphibian_sentence_239

There is a patch of specialized haircells, called papilla amphibiorum, in the inner ear capable of detecting deeper sounds. Amphibian_sentence_240

Another feature, unique to frogs and salamanders, is the columella-operculum complex adjoining the auditory capsule which is involved in the transmission of both airborne and seismic signals. Amphibian_sentence_241

The ears of salamanders and caecilians are less highly developed than those of frogs as they do not normally communicate with each other through the medium of sound. Amphibian_sentence_242

The eyes of tadpoles lack lids, but at metamorphosis, the cornea becomes more dome-shaped, the lens becomes flatter, and eyelids and associated glands and ducts develop. Amphibian_sentence_243

The adult eyes are an improvement on invertebrate eyes and were a first step in the development of more advanced vertebrate eyes. Amphibian_sentence_244

They allow colour vision and depth of focus. Amphibian_sentence_245

In the retinas are green rods, which are receptive to a wide range of wavelengths. Amphibian_sentence_246

Digestive and excretory systems Amphibian_section_11

Many amphibians catch their prey by flicking out an elongated tongue with a sticky tip and drawing it back into the mouth before seizing the item with their jaws. Amphibian_sentence_247

Some use inertial feeding to help them swallow the prey, repeatedly thrusting their head forward sharply causing the food to move backwards in their mouth by inertia. Amphibian_sentence_248

Most amphibians swallow their prey whole without much chewing so they possess voluminous stomachs. Amphibian_sentence_249

The short oesophagus is lined with cilia that help to move the food to the stomach and mucus produced by glands in the mouth and pharynx eases its passage. Amphibian_sentence_250

The enzyme chitinase produced in the stomach helps digest the chitinous cuticle of arthropod prey. Amphibian_sentence_251

Amphibians possess a pancreas, liver and gall bladder. Amphibian_sentence_252

The liver is usually large with two lobes. Amphibian_sentence_253

Its size is determined by its function as a glycogen and fat storage unit, and may change with the seasons as these reserves are built or used up. Amphibian_sentence_254

Adipose tissue is another important means of storing energy and this occurs in the abdomen (in internal structures called fat bodies), under the skin and, in some salamanders, in the tail. Amphibian_sentence_255

There are two kidneys located dorsally, near the roof of the body cavity. Amphibian_sentence_256

Their job is to filter the blood of metabolic waste and transport the urine via ureters to the urinary bladder where it is stored before being passed out periodically through the cloacal vent. Amphibian_sentence_257

Larvae and most aquatic adult amphibians excrete the nitrogen as ammonia in large quantities of dilute urine, while terrestrial species, with a greater need to conserve water, excrete the less toxic product urea. Amphibian_sentence_258

Some tree frogs with limited access to water excrete most of their metabolic waste as uric acid. Amphibian_sentence_259

Respiratory system Amphibian_section_12

The lungs in amphibians are primitive compared to those of amniotes, possessing few internal septa and large alveoli, and consequently having a comparatively slow diffusion rate for oxygen entering the blood. Amphibian_sentence_260

Ventilation is accomplished by buccal pumping. Amphibian_sentence_261

Most amphibians, however, are able to exchange gases with the water or air via their skin. Amphibian_sentence_262

To enable sufficient cutaneous respiration, the surface of their highly vascularised skin must remain moist to allow the oxygen to diffuse at a sufficiently high rate. Amphibian_sentence_263

Because oxygen concentration in the water increases at both low temperatures and high flow rates, aquatic amphibians in these situations can rely primarily on cutaneous respiration, as in the Titicaca water frog and the hellbender salamander. Amphibian_sentence_264

In air, where oxygen is more concentrated, some small species can rely solely on cutaneous gas exchange, most famously the plethodontid salamanders, which have neither lungs nor gills. Amphibian_sentence_265

Many aquatic salamanders and all tadpoles have gills in their larval stage, with some (such as the axolotl) retaining gills as aquatic adults. Amphibian_sentence_266

Reproduction Amphibian_section_13

See also: Sexual selection in amphibians Amphibian_sentence_267

For the purpose of reproduction most amphibians require fresh water although some lay their eggs on land and have developed various means of keeping them moist. Amphibian_sentence_268

A few (e.g. Fejervarya raja) can inhabit brackish water, but there are no true marine amphibians. Amphibian_sentence_269

There are reports, however, of particular amphibian populations unexpectedly invading marine waters. Amphibian_sentence_270

Such was the case with the Black Sea invasion of the natural hybrid Pelophylax esculentus reported in 2010. Amphibian_sentence_271

Several hundred frog species in adaptive radiations (e.g., Eleutherodactylus, the Pacific Platymantis, the Australo-Papuan microhylids, and many other tropical frogs), however, do not need any water for breeding in the wild. Amphibian_sentence_272

They reproduce via direct development, an ecological and evolutionary adaptation that has allowed them to be completely independent from free-standing water. Amphibian_sentence_273

Almost all of these frogs live in wet tropical rainforests and their eggs hatch directly into miniature versions of the adult, passing through the tadpole stage within the egg. Amphibian_sentence_274

Reproductive success of many amphibians is dependent not only on the quantity of rainfall, but the seasonal timing. Amphibian_sentence_275

In the tropics, many amphibians breed continuously or at any time of year. Amphibian_sentence_276

In temperate regions, breeding is mostly seasonal, usually in the spring, and is triggered by increasing day length, rising temperatures or rainfall. Amphibian_sentence_277

Experiments have shown the importance of temperature, but the trigger event, especially in arid regions, is often a storm. Amphibian_sentence_278

In anurans, males usually arrive at the breeding sites before females and the vocal chorus they produce may stimulate ovulation in females and the endocrine activity of males that are not yet reproductively active. Amphibian_sentence_279

In caecilians, fertilisation is internal, the male extruding an intromittent organ, the phallodeum, and inserting it into the female cloaca. Amphibian_sentence_280

The paired Müllerian glands inside the male cloaca secrete a fluid which resembles that produced by mammalian prostate glands and which may transport and nourish the sperm. Amphibian_sentence_281

Fertilisation probably takes place in the oviduct. Amphibian_sentence_282

The majority of salamanders also engage in internal fertilisation. Amphibian_sentence_283

In most of these, the male deposits a spermatophore, a small packet of sperm on top of a gelatinous cone, on the substrate either on land or in the water. Amphibian_sentence_284

The female takes up the sperm packet by grasping it with the lips of the cloaca and pushing it into the vent. Amphibian_sentence_285

The spermatozoa move to the spermatheca in the roof of the cloaca where they remain until ovulation which may be many months later. Amphibian_sentence_286

Courtship rituals and methods of transfer of the spermatophore vary between species. Amphibian_sentence_287

In some, the spermatophore may be placed directly into the female cloaca while in others, the female may be guided to the spermatophore or restrained with an embrace called amplexus. Amphibian_sentence_288

Certain primitive salamanders in the families Sirenidae, Hynobiidae and Cryptobranchidae practice external fertilisation in a similar manner to frogs, with the female laying the eggs in water and the male releasing sperm onto the egg mass. Amphibian_sentence_289

With a few exceptions, frogs use external fertilisation. Amphibian_sentence_290

The male grasps the female tightly with his forelimbs either behind the arms or in front of the back legs, or in the case of Epipedobates tricolor, around the neck. Amphibian_sentence_291

They remain in amplexus with their cloacae positioned close together while the female lays the eggs and the male covers them with sperm. Amphibian_sentence_292

Roughened nuptial pads on the male's hands aid in retaining grip. Amphibian_sentence_293

Often the male collects and retains the egg mass, forming a sort of basket with the hind feet. Amphibian_sentence_294

An exception is the granular poison frog (Oophaga granulifera) where the male and female place their cloacae in close proximity while facing in opposite directions and then release eggs and sperm simultaneously. Amphibian_sentence_295

The tailed frog (Ascaphus truei) exhibits internal fertilisation. Amphibian_sentence_296

The "tail" is only possessed by the male and is an extension of the cloaca and used to inseminate the female. Amphibian_sentence_297

This frog lives in fast-flowing streams and internal fertilisation prevents the sperm from being washed away before fertilisation occurs. Amphibian_sentence_298

The sperm may be retained in storage tubes attached to the oviduct until the following spring. Amphibian_sentence_299

Most frogs can be classified as either prolonged or explosive breeders. Amphibian_sentence_300

Typically, prolonged breeders congregate at a breeding site, the males usually arriving first, calling and setting up territories. Amphibian_sentence_301

Other satellite males remain quietly nearby, waiting for their opportunity to take over a territory. Amphibian_sentence_302

The females arrive sporadically, mate selection takes place and eggs are laid. Amphibian_sentence_303

The females depart and territories may change hands. Amphibian_sentence_304

More females appear and in due course, the breeding season comes to an end. Amphibian_sentence_305

Explosive breeders on the other hand are found where temporary pools appear in dry regions after rainfall. Amphibian_sentence_306

These frogs are typically species that emerge after heavy rains and congregate at a breeding site. Amphibian_sentence_307

They are attracted there by the calling of the first male to find a suitable place, perhaps a pool that forms in the same place each rainy season. Amphibian_sentence_308

The assembled frogs may call in unison and frenzied activity ensues, the males scrambling to mate with the usually smaller number of females. Amphibian_sentence_309

There is a direct competition between males to win the attention of the females in salamanders and newts, with elaborate courtship displays to keep the female's attention long enough to get her interested in choosing him to mate with. Amphibian_sentence_310

Some species store sperm through long breeding seasons, as the extra time may allow for interactions with rival sperm. Amphibian_sentence_311

Life cycle Amphibian_section_14

Most amphibians go through metamorphosis, a process of significant morphological change after birth. Amphibian_sentence_312

In typical amphibian development, eggs are laid in water and larvae are adapted to an aquatic lifestyle. Amphibian_sentence_313

Frogs, toads and salamanders all hatch from the egg as larvae with external gills. Amphibian_sentence_314

Metamorphosis in amphibians is regulated by thyroxine concentration in the blood, which stimulates metamorphosis, and prolactin, which counteracts thyroxine's effect. Amphibian_sentence_315

Specific events are dependent on threshold values for different tissues. Amphibian_sentence_316

Because most embryonic development is outside the parental body, it is subject to many adaptations due to specific environmental circumstances. Amphibian_sentence_317

For this reason tadpoles can have horny ridges instead of teeth, whisker-like skin extensions or fins. Amphibian_sentence_318

They also make use of a sensory lateral line organ similar to that of fish. Amphibian_sentence_319

After metamorphosis, these organs become redundant and will be reabsorbed by controlled cell death, called apoptosis. Amphibian_sentence_320

The variety of adaptations to specific environmental circumstances among amphibians is wide, with many discoveries still being made. Amphibian_sentence_321

Eggs Amphibian_section_15

The egg of an amphibian is typically surrounded by a transparent gelatinous covering secreted by the oviducts and containing mucoproteins and mucopolysaccharides. Amphibian_sentence_322

This capsule is permeable to water and gases, and swells considerably as it absorbs water. Amphibian_sentence_323

The ovum is at first rigidly held, but in fertilised eggs the innermost layer liquefies and allows the embryo to move freely. Amphibian_sentence_324

This also happens in salamander eggs, even when they are unfertilised. Amphibian_sentence_325

Eggs of some salamanders and frogs contain unicellular green algae. Amphibian_sentence_326

These penetrate the jelly envelope after the eggs are laid and may increase the supply of oxygen to the embryo through photosynthesis. Amphibian_sentence_327

They seem to both speed up the development of the larvae and reduce mortality. Amphibian_sentence_328

Most eggs contain the pigment melanin which raises their temperature through the absorption of light and also protects them against ultraviolet radiation. Amphibian_sentence_329

Caecilians, some plethodontid salamanders and certain frogs lay eggs underground that are unpigmented. Amphibian_sentence_330

In the wood frog (Rana sylvatica), the interior of the globular egg cluster has been found to be up to 6 °C (11 °F) warmer than its surroundings, which is an advantage in its cool northern habitat. Amphibian_sentence_331

The eggs may be deposited singly or in small groups, or may take the form of spherical egg masses, rafts or long strings. Amphibian_sentence_332

In terrestrial caecilians, the eggs are laid in grape-like clusters in burrows near streams. Amphibian_sentence_333

The amphibious salamander Ensatina attaches its similar clusters by stalks to underwater stems and roots. Amphibian_sentence_334

The greenhouse frog (Eleutherodactylus planirostris) lays eggs in small groups in the soil where they develop in about two weeks directly into juvenile frogs without an intervening larval stage. Amphibian_sentence_335

The tungara frog (Physalaemus pustulosus) builds a floating nest from foam to protect its eggs. Amphibian_sentence_336

First a raft is built, then eggs are laid in the centre, and finally a foam cap is overlaid. Amphibian_sentence_337

The foam has anti-microbial properties. Amphibian_sentence_338

It contains no detergents but is created by whipping up proteins and lectins secreted by the female. Amphibian_sentence_339

Larvae Amphibian_section_16

The eggs of amphibians are typically laid in water and hatch into free-living larvae that complete their development in water and later transform into either aquatic or terrestrial adults. Amphibian_sentence_340

In many species of frog and in most lungless salamanders (Plethodontidae), direct development takes place, the larvae growing within the eggs and emerging as miniature adults. Amphibian_sentence_341

Many caecilians and some other amphibians lay their eggs on land, and the newly hatched larvae wriggle or are transported to water bodies. Amphibian_sentence_342

Some caecilians, the alpine salamander (Salamandra atra) and some of the African live-bearing toads (Nectophrynoides spp.) are viviparous. Amphibian_sentence_343

Their larvae feed on glandular secretions and develop within the female's oviduct, often for long periods. Amphibian_sentence_344

Other amphibians, but not caecilians, are ovoviviparous. Amphibian_sentence_345

The eggs are retained in or on the parent's body, but the larvae subsist on the yolks of their eggs and receive no nourishment from the adult. Amphibian_sentence_346

The larvae emerge at varying stages of their growth, either before or after metamorphosis, according to their species. Amphibian_sentence_347

The toad genus Nectophrynoides exhibits all of these developmental patterns among its dozen or so members. Amphibian_sentence_348

Frogs Amphibian_section_17

Frog larvae are known as tadpoles and typically have oval bodies and long, vertically flattened tails with fins. Amphibian_sentence_349

The free-living larvae are normally fully aquatic, but the tadpoles of some species (such as Nannophrys ceylonensis) are semi-terrestrial and live among wet rocks. Amphibian_sentence_350

Tadpoles have cartilaginous skeletons, gills for respiration (external gills at first, internal gills later), lateral line systems and large tails that they use for swimming. Amphibian_sentence_351

Newly hatched tadpoles soon develop gill pouches that cover the gills. Amphibian_sentence_352

The lungs develop early and are used as accessory breathing organs, the tadpoles rising to the water surface to gulp air. Amphibian_sentence_353

Some species complete their development inside the egg and hatch directly into small frogs. Amphibian_sentence_354

These larvae do not have gills but instead have specialised areas of skin through which respiration takes place. Amphibian_sentence_355

While tadpoles do not have true teeth, in most species, the jaws have long, parallel rows of small keratinized structures called keradonts surrounded by a horny beak. Amphibian_sentence_356

Front legs are formed under the gill sac and hind legs become visible a few days later. Amphibian_sentence_357

Iodine and T4 (over stimulate the spectacular apoptosis [programmed cell death] of the cells of the larval gills, tail and fins) also stimulate the evolution of nervous systems transforming the aquatic, vegetarian tadpole into the terrestrial, carnivorous frog with better neurological, visuospatial, olfactory and cognitive abilities for hunting. Amphibian_sentence_358

In fact, tadpoles developing in ponds and streams are typically herbivorous. Amphibian_sentence_359

Pond tadpoles tend to have deep bodies, large caudal fins and small mouths; they swim in the quiet waters feeding on growing or loose fragments of vegetation. Amphibian_sentence_360

Stream dwellers mostly have larger mouths, shallow bodies and caudal fins; they attach themselves to plants and stones and feed on the surface films of algae and bacteria. Amphibian_sentence_361

They also feed on diatoms, filtered from the water through the gills, and stir up the sediment at bottom of the pond, ingesting edible fragments. Amphibian_sentence_362

They have a relatively long, spiral-shaped gut to enable them to digest this diet. Amphibian_sentence_363

Some species are carnivorous at the tadpole stage, eating insects, smaller tadpoles and fish. Amphibian_sentence_364

Young of the Cuban tree frog (Osteopilus septentrionalis) can occasionally be cannibalistic, the younger tadpoles attacking a larger, more developed tadpole when it is undergoing metamorphosis. Amphibian_sentence_365

At metamorphosis, rapid changes in the body take place as the lifestyle of the frog changes completely. Amphibian_sentence_366

The spiral‐shaped mouth with horny tooth ridges is reabsorbed together with the spiral gut. Amphibian_sentence_367

The animal develops a large jaw, and its gills disappear along with its gill sac. Amphibian_sentence_368

Eyes and legs grow quickly, and a tongue is formed. Amphibian_sentence_369

There are associated changes in the neural networks such as development of stereoscopic vision and loss of the lateral line system. Amphibian_sentence_370

All this can happen in about a day. Amphibian_sentence_371

A few days later, the tail is reabsorbed, due to the higher thyroxine concentration required for this to take place. Amphibian_sentence_372

Salamanders Amphibian_section_18

At hatching, a typical salamander larva has eyes without lids, teeth in both upper and lower jaws, three pairs of feathery external gills, a somewhat laterally flattened body and a long tail with dorsal and ventral fins. Amphibian_sentence_373

The forelimbs may be partially developed and the hind limbs are rudimentary in pond-living species but may be rather more developed in species that reproduce in moving water. Amphibian_sentence_374

Pond-type larvae often have a pair of balancers, rod-like structures on either side of the head that may prevent the gills from becoming clogged up with sediment. Amphibian_sentence_375

Some members of the genera Ambystoma and Dicamptodon have larvae that never fully develop into the adult form, but this varies with species and with populations. Amphibian_sentence_376

The northwestern salamander (Ambystoma gracile) is one of these and, depending on environmental factors, either remains permanently in the larval state, a condition known as neoteny, or transforms into an adult. Amphibian_sentence_377

Both of these are able to breed. Amphibian_sentence_378

Neoteny occurs when the animal's growth rate is very low and is usually linked to adverse conditions such as low water temperatures that may change the response of the tissues to the hormone thyroxine. Amphibian_sentence_379

Other factors that may inhibit metamorphosis include lack of food, lack of trace elements and competition from conspecifics. Amphibian_sentence_380

The tiger salamander (Ambystoma tigrinum) also sometimes behaves in this way and may grow particularly large in the process. Amphibian_sentence_381

The adult tiger salamander is terrestrial, but the larva is aquatic and able to breed while still in the larval state. Amphibian_sentence_382

When conditions are particularly inhospitable on land, larval breeding may allow continuation of a population that would otherwise die out. Amphibian_sentence_383

There are fifteen species of neotenic salamanders, including species of Necturus, Proteus and Amphiuma, and many examples of ones that adopt this strategy under appropriate environmental circumstances. Amphibian_sentence_384

Lungless salamanders in the family Plethodontidae are terrestrial and lay a small number of unpigmented eggs in a cluster among damp leaf litter. Amphibian_sentence_385

Each egg has a large yolk sac and the larva feeds on this while it develops inside the egg, emerging fully formed as a juvenile salamander. Amphibian_sentence_386

The female salamander often broods the eggs. Amphibian_sentence_387

In the genus Ensatinas, the female has been observed to coil around them and press her throat area against them, effectively massaging them with a mucous secretion. Amphibian_sentence_388

In newts and salamanders, metamorphosis is less dramatic than in frogs. Amphibian_sentence_389

This is because the larvae are already carnivorous and continue to feed as predators when they are adults so few changes are needed to their digestive systems. Amphibian_sentence_390

Their lungs are functional early, but the larvae do not make as much use of them as do tadpoles. Amphibian_sentence_391

Their gills are never covered by gill sacs and are reabsorbed just before the animals leave the water. Amphibian_sentence_392

Other changes include the reduction in size or loss of tail fins, the closure of gill slits, thickening of the skin, the development of eyelids, and certain changes in dentition and tongue structure. Amphibian_sentence_393

Salamanders are at their most vulnerable at metamorphosis as swimming speeds are reduced and transforming tails are encumbrances on land. Amphibian_sentence_394

Adult salamanders often have an aquatic phase in spring and summer, and a land phase in winter. Amphibian_sentence_395

For adaptation to a water phase, prolactin is the required hormone, and for adaptation to the land phase, thyroxine. Amphibian_sentence_396

External gills do not return in subsequent aquatic phases because these are completely absorbed upon leaving the water for the first time. Amphibian_sentence_397

Caecilians Amphibian_section_19

Most terrestrial caecilians that lay eggs do so in burrows or moist places on land near bodies of water. Amphibian_sentence_398

The development of the young of Ichthyophis glutinosus, a species from Sri Lanka, has been much studied. Amphibian_sentence_399

The eel-like larvae hatch out of the eggs and make their way to water. Amphibian_sentence_400

They have three pairs of external red feathery gills, a blunt head with two rudimentary eyes, a lateral line system and a short tail with fins. Amphibian_sentence_401

They swim by undulating their body from side to side. Amphibian_sentence_402

They are mostly active at night, soon lose their gills and make sorties onto land. Amphibian_sentence_403

Metamorphosis is gradual. Amphibian_sentence_404

By the age of about ten months they have developed a pointed head with sensory tentacles near the mouth and lost their eyes, lateral line systems and tails. Amphibian_sentence_405

The skin thickens, embedded scales develop and the body divides into segments. Amphibian_sentence_406

By this time, the caecilian has constructed a burrow and is living on land. Amphibian_sentence_407

In the majority of species of caecilians, the young are produced by viviparity. Amphibian_sentence_408

Typhlonectes compressicauda, a species from South America, is typical of these. Amphibian_sentence_409

Up to nine larvae can develop in the oviduct at any one time. Amphibian_sentence_410

They are elongated and have paired sac-like gills, small eyes and specialised scraping teeth. Amphibian_sentence_411

At first, they feed on the yolks of the eggs, but as this source of nourishment declines they begin to rasp at the ciliated epithelial cells that line the oviduct. Amphibian_sentence_412

This stimulates the secretion of fluids rich in lipids and mucoproteins on which they feed along with scrapings from the oviduct wall. Amphibian_sentence_413

They may increase their length sixfold and be two-fifths as long as their mother before being born. Amphibian_sentence_414

By this time they have undergone metamorphosis, lost their eyes and gills, developed a thicker skin and mouth tentacles, and reabsorbed their teeth. Amphibian_sentence_415

A permanent set of teeth grow through soon after birth. Amphibian_sentence_416

The ringed caecilian (Siphonops annulatus) has developed a unique adaptation for the purposes of reproduction. Amphibian_sentence_417

The progeny feed on a skin layer that is specially developed by the adult in a phenomenon known as maternal dermatophagy. Amphibian_sentence_418

The brood feed as a batch for about seven minutes at intervals of approximately three days which gives the skin an opportunity to regenerate. Amphibian_sentence_419

Meanwhile, they have been observed to ingest fluid exuded from the maternal cloaca. Amphibian_sentence_420

Parental care Amphibian_section_20

The care of offspring among amphibians has been little studied but, in general, the larger the number of eggs in a batch, the less likely it is that any degree of parental care takes place. Amphibian_sentence_421

Nevertheless, it is estimated that in up to 20% of amphibian species, one or both adults play some role in the care of the young. Amphibian_sentence_422

Those species that breed in smaller water bodies or other specialised habitats tend to have complex patterns of behaviour in the care of their young. Amphibian_sentence_423

Many woodland salamanders lay clutches of eggs under dead logs or stones on land. Amphibian_sentence_424

The black mountain salamander (Desmognathus welteri) does this, the mother brooding the eggs and guarding them from predation as the embryos feed on the yolks of their eggs. Amphibian_sentence_425

When fully developed, they break their way out of the egg capsules and disperse as juvenile salamanders. Amphibian_sentence_426

The male hellbender, a primitive salamander, excavates an underwater nest and encourages females to lay there. Amphibian_sentence_427

The male then guards the site for the two or three months before the eggs hatch, using body undulations to fan the eggs and increase their supply of oxygen. Amphibian_sentence_428

The male Colostethus subpunctatus, a tiny frog, protects the egg cluster which is hidden under a stone or log. Amphibian_sentence_429

When the eggs hatch, the male transports the tadpoles on his back, stuck there by a mucous secretion, to a temporary pool where he dips himself into the water and the tadpoles drop off. Amphibian_sentence_430

The male midwife toad (Alytes obstetricans) winds egg strings round his thighs and carries the eggs around for up to eight weeks. Amphibian_sentence_431

He keeps them moist and when they are ready to hatch, he visits a pond or ditch and releases the tadpoles. Amphibian_sentence_432

The female gastric-brooding frog (Rheobatrachus spp.) reared larvae in her stomach after swallowing either the eggs or hatchlings; however, this stage was never observed before the species became extinct. Amphibian_sentence_433

The tadpoles secrete a hormone that inhibits digestion in the mother whilst they develop by consuming their very large yolk supply. Amphibian_sentence_434

The pouched frog (Assa darlingtoni) lays eggs on the ground. Amphibian_sentence_435

When they hatch, the male carries the tadpoles around in brood pouches on his hind legs. Amphibian_sentence_436

The aquatic Surinam toad (Pipa pipa) raises its young in pores on its back where they remain until metamorphosis. Amphibian_sentence_437

The granular poison frog (Oophaga granulifera) is typical of a number of tree frogs in the poison dart frog family Dendrobatidae. Amphibian_sentence_438

Its eggs are laid on the forest floor and when they hatch, the tadpoles are carried one by one on the back of an adult to a suitable water-filled crevice such as the of a leaf or the rosette of a bromeliad. Amphibian_sentence_439

The female visits the nursery sites regularly and deposits unfertilised eggs in the water and these are consumed by the tadpoles. Amphibian_sentence_440

Feeding and diet Amphibian_section_21

With a few exceptions, adult amphibians are predators, feeding on virtually anything that moves that they can swallow. Amphibian_sentence_441

The diet mostly consists of small prey that do not move too fast such as beetles, caterpillars, earthworms and spiders. Amphibian_sentence_442

The sirens (Siren spp.) often ingest aquatic plant material with the invertebrates on which they feed and a Brazilian tree frog (Xenohyla truncata) includes a large quantity of fruit in its diet. Amphibian_sentence_443

The Mexican burrowing toad (Rhinophrynus dorsalis) has a specially adapted tongue for picking up ants and termites. Amphibian_sentence_444

It projects it with the tip foremost whereas other frogs flick out the rear part first, their tongues being hinged at the front. Amphibian_sentence_445

Food is mostly selected by sight, even in conditions of dim light. Amphibian_sentence_446

Movement of the prey triggers a feeding response. Amphibian_sentence_447

Frogs have been caught on fish hooks baited with red flannel and green frogs (Rana clamitans) have been found with stomachs full of elm seeds that they had seen floating past. Amphibian_sentence_448

Toads, salamanders and caecilians also use smell to detect prey. Amphibian_sentence_449

This response is mostly secondary because salamanders have been observed to remain stationary near odoriferous prey but only feed if it moves. Amphibian_sentence_450

Cave-dwelling amphibians normally hunt by smell. Amphibian_sentence_451

Some salamanders seem to have learned to recognize immobile prey when it has no smell, even in complete darkness. Amphibian_sentence_452

Amphibians usually swallow food whole but may chew it lightly first to subdue it. Amphibian_sentence_453

They typically have small hinged pedicellate teeth, a feature unique to amphibians. Amphibian_sentence_454

The base and crown of these are composed of dentine separated by an uncalcified layer and they are replaced at intervals. Amphibian_sentence_455

Salamanders, caecilians and some frogs have one or two rows of teeth in both jaws, but some frogs (Rana spp.) lack teeth in the lower jaw, and toads (Bufo spp.) have no teeth. Amphibian_sentence_456

In many amphibians there are also vomerine teeth attached to a facial bone in the roof of the mouth. Amphibian_sentence_457

The tiger salamander (Ambystoma tigrinum) is typical of the frogs and salamanders that hide under cover ready to ambush unwary invertebrates. Amphibian_sentence_458

Others amphibians, such as the Bufo spp. toads, actively search for prey, while the Argentine horned frog (Ceratophrys ornata) lures inquisitive prey closer by raising its hind feet over its back and vibrating its yellow toes. Amphibian_sentence_459

Among leaf litter frogs in Panama, frogs that actively hunt prey have narrow mouths and are slim, often brightly coloured and toxic, while ambushers have wide mouths and are broad and well-camouflaged. Amphibian_sentence_460

Caecilians do not flick their tongues, but catch their prey by grabbing it with their slightly backward-pointing teeth. Amphibian_sentence_461

The struggles of the prey and further jaw movements work it inwards and the caecilian usually retreats into its burrow. Amphibian_sentence_462

The subdued prey is gulped down whole. Amphibian_sentence_463

When they are newly hatched, frog larvae feed on the yolk of the egg. Amphibian_sentence_464

When this is exhausted some move on to feed on bacteria, algal crusts, detritus and raspings from submerged plants. Amphibian_sentence_465

Water is drawn in through their mouths, which are usually at the bottom of their heads, and passes through branchial food traps between their mouths and their gills where fine particles are trapped in mucus and filtered out. Amphibian_sentence_466

Others have specialised mouthparts consisting of a horny beak edged by several rows of labial teeth. Amphibian_sentence_467

They scrape and bite food of many kinds as well as stirring up the bottom sediment, filtering out larger particles with the papillae around their mouths. Amphibian_sentence_468

Some, such as the spadefoot toads, have strong biting jaws and are carnivorous or even cannibalistic. Amphibian_sentence_469

Vocalization Amphibian_section_22

The calls made by caecilians and salamanders are limited to occasional soft squeaks, grunts or hisses and have not been much studied. Amphibian_sentence_470

A clicking sound sometimes produced by caecilians may be a means of orientation, as in bats, or a form of communication. Amphibian_sentence_471

Most salamanders are considered voiceless, but the California giant salamander (Dicamptodon ensatus) has vocal cords and can produce a rattling or barking sound. Amphibian_sentence_472

Some species of salamander emit a quiet squeak or yelp if attacked. Amphibian_sentence_473

Frogs are much more vocal, especially during the breeding season when they use their voices to attract mates. Amphibian_sentence_474

The presence of a particular species in an area may be more easily discerned by its characteristic call than by a fleeting glimpse of the animal itself. Amphibian_sentence_475

In most species, the sound is produced by expelling air from the lungs over the vocal cords into an air sac or sacs in the throat or at the corner of the mouth. Amphibian_sentence_476

This may distend like a balloon and acts as a resonator, helping to transfer the sound to the atmosphere, or the water at times when the animal is submerged. Amphibian_sentence_477

The main vocalisation is the male's loud advertisement call which seeks to both encourage a female to approach and discourage other males from intruding on its territory. Amphibian_sentence_478

This call is modified to a quieter courtship call on the approach of a female or to a more aggressive version if a male intruder draws near. Amphibian_sentence_479

Calling carries the risk of attracting predators and involves the expenditure of much energy. Amphibian_sentence_480

Other calls include those given by a female in response to the advertisement call and a release call given by a male or female during unwanted attempts at amplexus. Amphibian_sentence_481

When a frog is attacked, a distress or fright call is emitted, often resembling a scream. Amphibian_sentence_482

The usually nocturnal Cuban tree frog (Osteopilus septentrionalis) produces a rain call when there is rainfall during daylight hours. Amphibian_sentence_483

Territorial behaviour Amphibian_section_23

Little is known of the territorial behaviour of caecilians, but some frogs and salamanders defend home ranges. Amphibian_sentence_484

These are usually feeding, breeding or sheltering sites. Amphibian_sentence_485

Males normally exhibit such behaviour though in some species, females and even juveniles are also involved. Amphibian_sentence_486

Although in many frog species, females are larger than males, this is not the case in most species where males are actively involved in territorial defence. Amphibian_sentence_487

Some of these have specific adaptations such as enlarged teeth for biting or spines on the chest, arms or thumbs. Amphibian_sentence_488

In salamanders, defence of a territory involves adopting an aggressive posture and if necessary attacking the intruder. Amphibian_sentence_489

This may involve snapping, chasing and sometimes biting, occasionally causing the loss of a tail. Amphibian_sentence_490

The behaviour of red back salamanders (Plethodon cinereus) has been much studied. Amphibian_sentence_491

91% of marked individuals that were later recaptured were within a metre (yard) of their original daytime retreat under a log or rock. Amphibian_sentence_492

A similar proportion, when moved experimentally a distance of 30 metres (98 ft), found their way back to their home base. Amphibian_sentence_493

The salamanders left odour marks around their territories which averaged 0.16 to 0.33 square metres (1.7 to 3.6 sq ft) in size and were sometimes inhabited by a male and female pair. Amphibian_sentence_494

These deterred the intrusion of others and delineated the boundaries between neighbouring areas. Amphibian_sentence_495

Much of their behaviour seemed stereotyped and did not involve any actual contact between individuals. Amphibian_sentence_496

An aggressive posture involved raising the body off the ground and glaring at the opponent who often turned away submissively. Amphibian_sentence_497

If the intruder persisted, a biting lunge was usually launched at either the tail region or the naso-labial grooves. Amphibian_sentence_498

Damage to either of these areas can reduce the fitness of the rival, either because of the need to regenerate tissue or because it impairs its ability to detect food. Amphibian_sentence_499

In frogs, male territorial behaviour is often observed at breeding locations; calling is both an announcement of ownership of part of this resource and an advertisement call to potential mates. Amphibian_sentence_500

In general, a deeper voice represents a heavier and more powerful individual, and this may be sufficient to prevent intrusion by smaller males. Amphibian_sentence_501

Much energy is used in the vocalization and it takes a toll on the territory holder who may be displaced by a fitter rival if he tires. Amphibian_sentence_502

There is a tendency for males to tolerate the holders of neighbouring territories while vigorously attacking unknown intruders. Amphibian_sentence_503

Holders of territories have a "home advantage" and usually come off better in an encounter between two similar-sized frogs. Amphibian_sentence_504

If threats are insufficient, chest to chest tussles may take place. Amphibian_sentence_505

Fighting methods include pushing and shoving, deflating the opponent's vocal sac, seizing him by the head, jumping on his back, biting, chasing, splashing, and ducking him under the water. Amphibian_sentence_506

Defence mechanisms Amphibian_section_24

Amphibians have soft bodies with thin skins, and lack claws, defensive armour, or spines. Amphibian_sentence_507

Nevertheless, they have evolved various defence mechanisms to keep themselves alive. Amphibian_sentence_508

The first line of defence in salamanders and frogs is the mucous secretion that they produce. Amphibian_sentence_509

This keeps their skin moist and makes them slippery and difficult to grip. Amphibian_sentence_510

The secretion is often sticky and distasteful or toxic. Amphibian_sentence_511

Snakes have been observed yawning and gaping when trying to swallow African clawed frogs (Xenopus laevis), which gives the frogs an opportunity to escape. Amphibian_sentence_512

Caecilians have been little studied in this respect, but the Cayenne caecilian (Typhlonectes compressicauda) produces toxic mucus that has killed predatory fish in a feeding experiment in Brazil. Amphibian_sentence_513

In some salamanders, the skin is poisonous. Amphibian_sentence_514

The rough-skinned newt (Taricha granulosa) from North America and other members of its genus contain the neurotoxin tetrodotoxin (TTX), the most toxic non-protein substance known and almost identical to that produced by pufferfish. Amphibian_sentence_515

Handling the newts does not cause harm, but ingestion of even the most minute amounts of the skin is deadly. Amphibian_sentence_516

In feeding trials, fish, frogs, reptiles, birds and mammals were all found to be susceptible. Amphibian_sentence_517

The only predators with some tolerance to the poison are certain populations of common garter snake (Thamnophis sirtalis). Amphibian_sentence_518

In locations where both snake and salamander co-exist, the snakes have developed immunity through genetic changes and they feed on the amphibians with impunity. Amphibian_sentence_519

Coevolution occurs with the newt increasing its toxic capabilities at the same rate as the snake further develops its immunity. Amphibian_sentence_520

Some frogs and toads are toxic, the main poison glands being at the side of the neck and under the warts on the back. Amphibian_sentence_521

These regions are presented to the attacking animal and their secretions may be foul-tasting or cause various physical or neurological symptoms. Amphibian_sentence_522

Altogether, over 200 toxins have been isolated from the limited number of amphibian species that have been investigated. Amphibian_sentence_523

Poisonous species often use bright colouring to warn potential predators of their toxicity. Amphibian_sentence_524

These warning colours tend to be red or yellow combined with black, with the fire salamander (Salamandra salamandra) being an example. Amphibian_sentence_525

Once a predator has sampled one of these, it is likely to remember the colouration next time it encounters a similar animal. Amphibian_sentence_526

In some species, such as the fire-bellied toad (Bombina spp.), the warning colouration is on the belly and these animals adopt a defensive pose when attacked, exhibiting their bright colours to the predator. Amphibian_sentence_527

The frog Allobates zaparo is not poisonous, but mimics the appearance of other toxic species in its locality, a strategy that may deceive predators. Amphibian_sentence_528

Many amphibians are nocturnal and hide during the day, thereby avoiding diurnal predators that hunt by sight. Amphibian_sentence_529

Other amphibians use camouflage to avoid being detected. Amphibian_sentence_530

They have various colourings such as mottled browns, greys and olives to blend into the background. Amphibian_sentence_531

Some salamanders adopt defensive poses when faced by a potential predator such as the North American northern short-tailed shrew (Blarina brevicauda). Amphibian_sentence_532

Their bodies writhe and they raise and lash their tails which makes it difficult for the predator to avoid contact with their poison-producing granular glands. Amphibian_sentence_533

A few salamanders will autotomise their tails when attacked, sacrificing this part of their anatomy to enable them to escape. Amphibian_sentence_534

The tail may have a constriction at its base to allow it to be easily detached. Amphibian_sentence_535

The tail is regenerated later, but the energy cost to the animal of replacing it is significant. Amphibian_sentence_536

Some frogs and toads inflate themselves to make themselves look large and fierce, and some spadefoot toads (Pelobates spp) scream and leap towards the attacker. Amphibian_sentence_537

Giant salamanders of the genus Andrias, as well as Ceratophrine and Pyxicephalus frogs possess sharp teeth and are capable of drawing blood with a defensive bite. Amphibian_sentence_538

The blackbelly salamander (Desmognathus quadramaculatus) can bite an attacking common garter snake (Thamnophis sirtalis) two or three times its size on the head and often manages to escape. Amphibian_sentence_539

Cognition Amphibian_section_25

In amphibians, there is evidence of habituation, associative learning through both classical and instrumental learning, and discrimination abilities. Amphibian_sentence_540

In one experiment, when offered live fruit flies (Drosophila virilis), salamanders chose the larger of 1 vs 2 and 2 vs 3. Amphibian_sentence_541

Frogs can distinguish between low numbers (1 vs 2, 2 vs 3, but not 3 vs 4) and large numbers (3 vs 6, 4 vs 8, but not 4 vs 6) of prey. Amphibian_sentence_542

This is irrespective of other characteristics, i.e. surface area, volume, weight and movement, although discrimination among large numbers may be based on surface area. Amphibian_sentence_543

Conservation Amphibian_section_26

Main article: Decline in amphibian populations Amphibian_sentence_544

Dramatic declines in amphibian populations, including population crashes and mass localized extinction, have been noted since the late 1980s from locations all over the world, and amphibian declines are thus perceived to be one of the most critical threats to global biodiversity. Amphibian_sentence_545

In 2004, the International Union for Conservation of Nature (IUCN) reported stating that currently birds, mammals, and amphibians extinction rates were at minimum 48 times greater than natural extinction rates—possibly 1,024 times higher. Amphibian_sentence_546

In 2006 there were believed to be 4,035 species of amphibians that depended on water at some stage during their life cycle. Amphibian_sentence_547

Of these, 1,356 (33.6%) were considered to be threatened and this figure is likely to be an underestimate because it excludes 1,427 species for which there was insufficient data to assess their status. Amphibian_sentence_548

A number of causes are believed to be involved, including habitat destruction and modification, over-exploitation, pollution, introduced species, global warming, endocrine-disrupting pollutants, destruction of the ozone layer (ultraviolet radiation has shown to be especially damaging to the skin, eyes, and eggs of amphibians), and diseases like chytridiomycosis. Amphibian_sentence_549

However, many of the causes of amphibian declines are still poorly understood, and are a topic of ongoing discussion. Amphibian_sentence_550

With their complex reproductive needs and permeable skins, amphibians are often considered to be ecological indicators. Amphibian_sentence_551

In many terrestrial ecosystems, they constitute one of the largest parts of the vertebrate biomass. Amphibian_sentence_552

Any decline in amphibian numbers will affect the patterns of predation. Amphibian_sentence_553

The loss of carnivorous species near the top of the food chain will upset the delicate ecosystem balance and may cause dramatic increases in opportunistic species. Amphibian_sentence_554

In the Middle East, a growing appetite for eating frog legs and the consequent gathering of them for food was linked to an increase in mosquitoes. Amphibian_sentence_555

Predators that feed on amphibians are affected by their decline. Amphibian_sentence_556

The western terrestrial garter snake (Thamnophis elegans) in California is largely aquatic and depends heavily on two species of frog that are decreasing in numbers, the Yosemite toad (Bufo canorus) and the mountain yellow-legged frog (Rana muscosa), putting the snake's future at risk. Amphibian_sentence_557

If the snake were to become scarce, this would affect birds of prey and other predators that feed on it. Amphibian_sentence_558

Meanwhile, in the ponds and lakes, fewer frogs means fewer tadpoles. Amphibian_sentence_559

These normally play an important role in controlling the growth of algae and also forage on detritus that accumulates as sediment on the bottom. Amphibian_sentence_560

A reduction in the number of tadpoles may lead to an overgrowth of algae, resulting in depletion of oxygen in the water when the algae later die and decompose. Amphibian_sentence_561

Aquatic invertebrates and fish might then die and there would be unpredictable ecological consequences. Amphibian_sentence_562

A global strategy to stem the crisis was released in 2005 in the form of the Amphibian Conservation Action Plan. Amphibian_sentence_563

Developed by over eighty leading experts in the field, this call to action details what would be required to curtail amphibian declines and extinctions over the following five years and how much this would cost. Amphibian_sentence_564

The Amphibian Specialist Group of the IUCN is spearheading efforts to implement a comprehensive global strategy for amphibian conservation. Amphibian_sentence_565

Amphibian Ark is an organization that was formed to implement the ex-situ conservation recommendations of this plan, and they have been working with zoos and aquaria around the world, encouraging them to create assurance colonies of threatened amphibians. Amphibian_sentence_566

One such project is the Panama Amphibian Rescue and Conservation Project that built on existing conservation efforts in Panama to create a country-wide response to the threat of chytridiomycosis. Amphibian_sentence_567

See also Amphibian_section_27


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