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and limbs can be regenerated. adult frogs are unable to regrow limbs but tadpoles can do so. circulatory system amphibians have a juvenile stage and an adult stage, and the circulatory systems of the two are distinct. 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. in the adult stage, amphibians (especially frogs) lose their gills and develop lungs. they have a heart that consists of a single ventricle and two atria. when the ventricle starts contracting, deoxygenated blood is pumped through the pulmonary artery to the lungs. continued contraction then pumps oxygenated blood around the rest of the body. mixing of the two bloodstreams

is minimized by the anatomy of the chambers. nervous and sensory systems the nervous system is basically the same as in other vertebrates, with a central brain, a spinal cord, and nerves throughout the body. 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. it is believed amphibians are capable of perceiving pain. the brain consists of equal parts, cerebrum, midbrain and cerebellum. 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. the cerebellum is the center of muscular coordination and the medulla oblongata controls some organ functions including heartbeat and respiration. the brain sends

signals through the spinal cord and nerves to regulate activity in the rest of the body. the pineal body, known to regulate sleep patterns in humans, is thought to produce the hormones involved in hibernation and aestivation in amphibians. tadpoles retain the lateral line system of their ancestral fishes, but this is lost in terrestrial adult amphibians. some caecilians possess electroreceptors that allow them to locate objects around them when submerged in water. the ears are well developed in frogs. there is no external ear, but the large circular eardrum lies on the surface of the head just behind the eye. this vibrates and sound is transmitted through a single bone, the stapes, to the inner ear. only high-frequency sounds like mating calls are heard in this way, but low-frequency noises can be detected through

another mechanism. there is a patch of specialized haircells, called papilla amphibiorum, in the inner ear capable of detecting deeper sounds. 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. 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. 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. the adult eyes are an improvement on invertebrate eyes and were a first step in the development of more advanced vertebrate eyes. they allow colour

vision and depth of focus. in the retinas are green rods, which are receptive to a wide range of wavelengths. digestive and excretory systems 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. 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. most amphibians swallow their prey whole without much chewing so they possess voluminous stomachs. 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. the enzyme chitinase produced in the stomach helps digest the chitinous cuticle of arthropod

prey. amphibians possess a pancreas, liver and gall bladder. the liver is usually large with two lobes. 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. 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. there are two kidneys located dorsally, near the roof of the body cavity. 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. 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. some tree frogs with limited access to water excrete most of their metabolic waste as uric acid. respiratory system 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. ventilation is accomplished by buccal pumping. most amphibians, however, are able to exchange gases with the water or air via their skin. 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. 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. 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. many aquatic salamanders and all tadpoles have gills in their larval stage, with some (such as the axolotl) retaining gills as aquatic adults. reproduction 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. a few (e.g. fejervarya raja) can inhabit brackish water, but there are no true marine amphibians. there are reports, however, of particular amphibian populations unexpectedly

invading marine waters. such was the case with the black sea invasion of the natural hybrid pelophylax esculentus reported in 2010. 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. they reproduce via direct development, an ecological and evolutionary adaptation that has allowed them to be completely independent from free-standing water. 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. reproductive success of many amphibians is dependent not only on the quantity of rainfall, but the seasonal timing. in the tropics,

many amphibians breed continuously or at any time of year. in temperate regions, breeding is mostly seasonal, usually in the spring, and is triggered by increasing day length, rising temperatures or rainfall. experiments have shown the importance of temperature, but the trigger event, especially in arid regions, is often a storm. 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. in caecilians, fertilisation is internal, the male extruding an intromittent organ, the , and inserting it into the female cloaca. the paired mullerian glands inside the male cloaca secrete a fluid which resembles that produced by mammalian prostate glands and which may transport

and nourish the sperm. fertilisation probably takes place in the oviduct. the majority of salamanders also engage in internal fertilisation. 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. the female takes up the sperm packet by grasping it with the lips of the cloaca and pushing it into the vent. the spermatozoa move to the spermatheca in the roof of the cloaca where they remain until ovulation which may be many months later. courtship rituals and methods of transfer of the spermatophore vary between species. 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. 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. with a few exceptions, frogs use external fertilisation. 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. they remain in amplexus with their cloacae positioned close together while the female lays the eggs and the male covers them with sperm. roughened nuptial pads on the male's hands aid in retaining grip. often the male collects and retains the egg mass, forming a sort of basket with the hind feet. 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. the tailed frog (ascaphus truei) exhibits internal fertilisation. the "tail" is only possessed by the male and is an extension of the cloaca and used to inseminate the female. this frog lives in fast-flowing streams and internal fertilisation prevents the sperm from being washed away before fertilisation occurs. the sperm may be retained in storage tubes attached to the oviduct until the following spring. most frogs can be classified as either prolonged or explosive breeders. typically, prolonged breeders congregate at a breeding site, the males usually arriving first, calling and setting up territories. other satellite males remain quietly nearby, waiting for their opportunity

to take over a territory. the females arrive sporadically, mate selection takes place and eggs are laid. the females depart and territories may change hands. more females appear and in due course, the breeding season comes to an end. explosive breeders on the other hand are found where temporary pools appear in dry regions after rainfall. these frogs are typically fossorial species that emerge after heavy rains and congregate at a breeding site. 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. the assembled frogs may call in unison and frenzied activity ensues, the males scrambling to mate with the usually smaller number of females. 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. some species store sperm through long breeding seasons, as the extra time may allow for interactions with rival sperm. life cycle most amphibians go through metamorphosis, a process of significant morphological change after birth. in typical amphibian development, eggs are laid in water and larvae are adapted to an aquatic lifestyle. frogs, toads and salamanders all hatch from the egg as larvae with external gills. metamorphosis in amphibians is regulated by thyroxine concentration in the blood, which stimulates metamorphosis, and prolactin, which counteracts thyroxine's effect. specific events are dependent on threshold values for different tissues. because

most embryonic development is outside the parental body, it is subject to many adaptations due to specific environmental circumstances. for this reason tadpoles can have horny ridges instead of teeth, whisker-like skin extensions or fins. they also make use of a sensory lateral line organ similar to that of fish. after metamorphosis, these organs become redundant and will be reabsorbed by controlled cell death, called apoptosis. the variety of adaptations to specific environmental circumstances among amphibians is wide, with many discoveries still being made. eggs the egg of an amphibian is typically surrounded by a transparent gelatinous covering secreted by the oviducts and containing mucoproteins and mucopolysaccharides. this capsule is permeable to water and gases, and swells considerably as it absorbs

water. the ovum is at first rigidly held, but in fertilised eggs the innermost layer liquefies and allows the embryo to move freely. this also happens in salamander eggs, even when they are unfertilised. eggs of some salamanders and frogs contain unicellular green algae. these penetrate the jelly envelope after the eggs are laid and may increase the supply of oxygen to the embryo through photosynthesis. they seem to both speed up the development of the larvae and reduce mortality. most eggs contain the pigment melanin which raises their temperature through the absorption of light and also protects them against ultraviolet radiation. caecilians, some plethodontid salamanders and certain frogs lay eggs underground that are unpigmented. in the wood frog (rana sylvatica), the interior of the globular egg cluster

has been found to be up to warmer than its surroundings, which is an advantage in its cool northern habitat. the eggs may be deposited singly or in small groups, or may take the form of spherical egg masses, rafts or long strings. in terrestrial caecilians, the eggs are laid in grape-like clusters in burrows near streams. the amphibious salamander ensatina attaches its similar clusters by stalks to underwater stems and roots. 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. the tungara frog (physalaemus pustulosus) builds a floating nest from foam to protect its eggs. first a raft is built, then eggs are laid in the centre, and finally a foam cap is overlaid. the foam

has anti-microbial properties. it contains no detergents but is created by whipping up proteins and lectins secreted by the female. larvae 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. 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. many caecilians and some other amphibians lay their eggs on land, and the newly hatched larvae wriggle or are transported to water bodies. some caecilians, the alpine salamander (salamandra atra) and some of the african live-bearing toads (nectophrynoides spp.) are viviparous. their larvae feed on glandular secretions

and develop within the female's oviduct, often for long periods. other amphibians, but not caecilians, are ovoviviparous. 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. the larvae emerge at varying stages of their growth, either before or after metamorphosis, according to their species. the toad genus nectophrynoides exhibits all of these developmental patterns among its dozen or so members. frogs frog larvae are known as tadpoles and typically have oval bodies and long, vertically flattened tails with fins. 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. 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. newly hatched tadpoles soon develop gill pouches that cover the gills. the lungs develop early and are used as accessory breathing organs, the tadpoles rising to the water surface to gulp air. some species complete their development inside the egg and hatch directly into small frogs. these larvae do not have gills but instead have specialised areas of skin through which respiration takes place. 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. front legs are formed under the gill sac and hind legs become visible a few days later. 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. in fact, tadpoles developing in ponds and streams are typically herbivorous. 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. 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. 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. they have a relatively long, spiral-shaped gut to enable them to digest this diet. some species are carnivorous at the tadpole stage, eating insects, smaller tadpoles and fish. 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. at metamorphosis, rapid changes in the body take place as the lifestyle of the frog changes completely. the spiralshaped mouth with horny tooth ridges is reabsorbed together with the spiral gut. the animal develops a large jaw, and its gills disappear along with its gill sac. eyes and legs grow quickly, and a tongue is formed. there are associated changes in the neural networks such as development of stereoscopic

vision and loss of the lateral line system. all this can happen in about a day. a few days later, the tail is reabsorbed, due to the higher thyroxine concentration required for this to take place. salamanders 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. 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. 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. 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. 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. both of these are able to breed. 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. other factors that may inhibit metamorphosis include lack of food, lack of trace elements and competition from conspecifics. the tiger salamander (ambystoma tigrinum) also sometimes behaves in this way and may grow particularly large in the process. the adult tiger

salamander is terrestrial, but the larva is aquatic and able to breed while still in the larval state. when conditions are particularly inhospitable on land, larval breeding may allow continuation of a population that would otherwise die out. there are fifteen species of obligate neotenic salamanders, including species of necturus, proteus and amphiuma, and many examples of facultative ones that adopt this strategy under appropriate environmental circumstances. lungless salamanders in the family plethodontidae are terrestrial and lay a small number of unpigmented eggs in a cluster among damp leaf litter. 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. the female salamander often broods the eggs. 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. in newts and salamanders, metamorphosis is less dramatic than in frogs. 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. their lungs are functional early, but the larvae do not make as much use of them as do tadpoles. their gills are never covered by gill sacs and are reabsorbed just before the animals leave the water. 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. salamanders are at their most vulnerable at metamorphosis

as swimming speeds are reduced and transforming tails are encumbrances on land. adult salamanders often have an aquatic phase in spring and summer, and a land phase in winter. for adaptation to a water phase, prolactin is the required hormone, and for adaptation to the land phase, thyroxine. external gills do not return in subsequent aquatic phases because these are completely absorbed upon leaving the water for the first time. caecilians most terrestrial caecilians that lay eggs do so in burrows or moist places on land near bodies of water. the development of the young of ichthyophis glutinosus, a species from sri lanka, has been much studied. the eel-like larvae hatch out of the eggs and make their way to water. 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. they swim by undulating their body from side to side. they are mostly active at night, soon lose their gills and make sorties onto land. metamorphosis is gradual. 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. the skin thickens, embedded scales develop and the body divides into segments. by this time, the caecilian has constructed a burrow and is living on land. in the majority of species of caecilians, the young are produced by viviparity. typhlonectes compressicauda, a species from south america, is typical of these. up to nine larvae can develop in the oviduct at any one time. they are elongated and have paired sac-like gills, small eyes and specialised

scraping teeth. 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. this stimulates the secretion of fluids rich in lipids and mucoproteins on which they feed along with scrapings from the oviduct wall. they may increase their length sixfold and be two-fifths as long as their mother before being born. by this time they have undergone metamorphosis, lost their eyes and gills, developed a thicker skin and mouth tentacles, and reabsorbed their teeth. a permanent set of teeth grow through soon after birth. the ringed caecilian (siphonops annulatus) has developed a unique adaptation for the purposes of reproduction. the progeny feed on a skin layer that is specially developed by the adult in a phenomenon

known as maternal dermatophagy. the brood feed as a batch for about seven minutes at intervals of approximately three days which gives the skin an opportunity to regenerate. meanwhile, they have been observed to ingest fluid exuded from the maternal cloaca. parental care 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. 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. 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. many woodland salamanders lay clutches of eggs under dead logs or stones on

land. 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. when fully developed, they break their way out of the egg capsules and disperse as juvenile salamanders. the male hellbender, a primitive salamander, excavates an underwater nest and encourages females to lay there. 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. the male colostethus subpunctatus, a tiny frog, protects the egg cluster which is hidden under a stone or log. 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. the male midwife toad (alytes obstetricans) winds egg strings round his thighs and carries the eggs around for up to eight weeks. he keeps them moist and when they are ready to hatch, he visits a pond or ditch and releases the tadpoles. 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. the tadpoles secrete a hormone that inhibits digestion in the mother whilst they develop by consuming their very large yolk supply. the pouched frog (assa darlingtoni) lays eggs on the ground. when they hatch, the male carries the tadpoles around in brood pouches on his hind legs. the aquatic surinam toad (pipa pipa) raises its young in pores on its

back where they remain until metamorphosis. the granular poison frog (oophaga granulifera) is typical of a number of tree frogs in the poison dart frog family dendrobatidae. 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 axil of a leaf or the rosette of a bromeliad. the female visits the nursery sites regularly and deposits unfertilised eggs in the water and these are consumed by the tadpoles. genetics and genomics amphibians are notable among vertebrates for their diversity of chromosomes and genomes. the karyotypes (chromosomes) have been determined for at least 1,193 (14.5%) of the ~8,200 known (diploid) species, including 963 anurans, 209 salamanders, and 21 caecilians. generally, the karyotypes

of diploid amphibians are characterized by 2026 bi-armed chromosomes. amphibians have also very large genomes compared to other taxa of vertebrates and corresponding variation in genome size (c-value: picograms of dna in haploid nuclei). the genome sizes range from 0.95 to 11.5 pg in frogs, from 13.89 to 120.56 pg in salamanders, and from 2.94 to 11.78 pg in caecilians. the large genome sizes have prevented whole-genome sequencing of amphibians although a number of genomes have been published recently. the 1.7gb draft genome of xenopus tropicalis was the first to be reported for amphibians in 2010. compared to some salamanders this frog genome is tiny. for instance, the genome of the mexican axolotl turned out to be 32 gb, which is more than 10 times larger than the human genome (3gb). feeding and diet with

a few exceptions, adult amphibians are predators, feeding on virtually anything that moves that they can swallow. the diet mostly consists of small prey that do not move too fast such as beetles, caterpillars, earthworms and spiders. 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. the mexican burrowing toad (rhinophrynus dorsalis) has a specially adapted tongue for picking up ants and termites. it projects it with the tip foremost whereas other frogs flick out the rear part first, their tongues being hinged at the front. food is mostly selected by sight, even in conditions of dim light. movement of the prey triggers a feeding response. 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. toads, salamanders and caecilians also use smell to detect prey. this response is mostly secondary because salamanders have been observed to remain stationary near odoriferous prey but only feed if it moves. cave-dwelling amphibians normally hunt by smell. some salamanders seem to have learned to recognize immobile prey when it has no smell, even in complete darkness. amphibians usually swallow food whole but may chew it lightly first to subdue it. they typically have small hinged pedicellate teeth, a feature unique to amphibians. the base and crown of these are composed of dentine separated by an uncalcified layer and they are replaced at intervals. 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. in many amphibians there are also vomerine teeth attached to a facial bone in the roof of the mouth. the tiger salamander (ambystoma tigrinum) is typical of the frogs and salamanders that hide under cover ready to ambush unwary invertebrates. 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. 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.

caecilians do not flick their tongues, but catch their prey by grabbing it with their slightly backward-pointing teeth. the struggles of the prey and further jaw movements work it inwards and the caecilian usually retreats into its burrow. the subdued prey is gulped down whole. when they are newly hatched, frog larvae feed on the yolk of the egg. when this is exhausted some move on to feed on bacteria, algal crusts, detritus and raspings from submerged plants. 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. others have specialised mouthparts consisting of a horny beak edged by several rows of labial teeth. 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. some, such as the spadefoot toads, have strong biting jaws and are carnivorous or even cannibalistic. vocalization the calls made by caecilians and salamanders are limited to occasional soft squeaks, grunts or hisses and have not been much studied. a clicking sound sometimes produced by caecilians may be a means of orientation, as in bats, or a form of communication. most salamanders are considered voiceless, but the california giant salamander (dicamptodon ensatus) has vocal cords and can produce a rattling or barking sound. some species of salamander emit a quiet squeak or yelp if attacked. frogs are much more vocal, especially during the breeding season when they use their voices

to attract mates. 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. 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. 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. 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. 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. calling carries the

risk of attracting predators and involves the expenditure of much energy. 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. when a frog is attacked, a distress or fright call is emitted, often resembling a scream. the usually nocturnal cuban tree frog (osteopilus septentrionalis) produces a rain call when there is rainfall during daylight hours. territorial behaviour little is known of the territorial behaviour of caecilians, but some frogs and salamanders defend home ranges. these are usually feeding, breeding or sheltering sites. males normally exhibit such behaviour though in some species, females and even juveniles are also involved. 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. some of these have specific adaptations such as enlarged teeth for biting or spines on the chest, arms or thumbs. in salamanders, defence of a territory involves adopting an aggressive posture and if necessary attacking the intruder. this may involve snapping, chasing and sometimes biting, occasionally causing the loss of a tail. the behaviour of red back salamanders (plethodon cinereus) has been much studied. 91% of marked individuals that were later recaptured were within a metre (yard) of their original daytime retreat under a log or rock. a similar proportion, when moved experimentally a distance of , found their way back to their home base. the salamanders left odour marks around their territories which averaged

in size and were sometimes inhabited by a male and female pair. these deterred the intrusion of others and delineated the boundaries between neighbouring areas. much of their behaviour seemed stereotyped and did not involve any actual contact between individuals. an aggressive posture involved raising the body off the ground and glaring at the opponent who often turned away submissively. if the intruder persisted, a biting lunge was usually launched at either the tail region or the naso-labial grooves. 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. 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. in general, a deeper voice represents a heavier and more powerful individual, and this may be sufficient to prevent intrusion by smaller males. 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. there is a tendency for males to tolerate the holders of neighbouring territories while vigorously attacking unknown intruders. holders of territories have a "home advantage" and usually come off better in an encounter between two similar-sized frogs. if threats are insufficient, chest to chest tussles may take place. 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. defence mechanisms amphibians have soft bodies with thin skins, and lack claws, defensive armour, or spines. nevertheless, they have evolved various defence mechanisms to keep themselves alive. the first line of defence in salamanders and frogs is the mucous secretion that they produce. this keeps their skin moist and makes them slippery and difficult to grip. the secretion is often sticky and distasteful or toxic. snakes have been observed yawning and gaping when trying to swallow african clawed frogs (xenopus laevis), which gives the frogs an opportunity to escape. 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. in some salamanders, the skin is poisonous.

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. handling the newts does not cause harm, but ingestion of even the most minute amounts of the skin is deadly. in feeding trials, fish, frogs, reptiles, birds and mammals were all found to be susceptible. the only predators with some tolerance to the poison are certain populations of common garter snake (thamnophis sirtalis). 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. coevolution occurs with the newt increasing its toxic capabilities at the same rate as the snake further

develops its immunity. some frogs and toads are toxic, the main poison glands being at the side of the neck and under the warts on the back. these regions are presented to the attacking animal and their secretions may be foul-tasting or cause various physical or neurological symptoms. altogether, over 200 toxins have been isolated from the limited number of amphibian species that have been investigated. poisonous species often use bright colouring to warn potential predators of their toxicity. these warning colours tend to be red or yellow combined with black, with the fire salamander (salamandra salamandra) being an example. once a predator has sampled one of these, it is likely to remember the colouration next time it encounters a similar animal. 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. the frog allobates zaparo is not poisonous, but mimics the appearance of other toxic species in its locality, a strategy that may deceive predators. many amphibians are nocturnal and hide during the day, thereby avoiding diurnal predators that hunt by sight. other amphibians use camouflage to avoid being detected. they have various colourings such as mottled browns, greys and olives to blend into the background. some salamanders adopt defensive poses when faced by a potential predator such as the north american northern short-tailed shrew (blarina brevicauda). 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. a few salamanders will autotomise their tails when attacked, sacrificing this part of their anatomy to enable them to escape. the tail may have a constriction at its base to allow it to be easily detached. the tail is regenerated later, but the energy cost to the animal of replacing it is significant. 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. 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. 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. cognition in amphibians, there is evidence of habituation, associative learning through both classical and instrumental learning, and discrimination abilities. in one experiment, when offered live fruit flies (drosophila virilis), salamanders chose the larger of 1 vs 2 and 2 vs 3. 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. 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. conservation 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. 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 ratespossibly 1,024 times higher. in 2006, there were believed to be 4,035 species of amphibians that depended on water at some stage during their life cycle. 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. 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. however, many of the causes of amphibian declines are still poorly understood, and are a topic of ongoing discussion. with their complex reproductive needs and permeable skins, amphibians are often considered to be ecological indicators. in many terrestrial ecosystems, they constitute one of the largest parts of the vertebrate biomass. any decline in amphibian numbers will affect the patterns of predation. 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. 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. predators that feed on amphibians are affected by their decline. 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. if the snake were to become scarce, this would affect birds of prey and other predators that feed on it. meanwhile, in the ponds and lakes, fewer frogs means fewer tadpoles. these normally play an important role in controlling the growth of algae and also forage on detritus that accumulates as sediment on the bottom. 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. aquatic invertebrates and fish might then die and there would be unpredictable ecological consequences. a global strategy to stem the crisis was released in 2005 in the form of the amphibian conservation action plan. 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. the amphibian specialist group of the iucn is spearheading efforts to implement a comprehensive global strategy for amphibian conservation. 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. 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. see also list of amphibians list of amphibian genera list of threatened reptiles and amphibians of the united states references cited texts further reading external links amphibians animalspot.net archeozootheque : amphibians skeletons drawings : available in vector, image and pdf formats amphibian specialist group amphibian ark amphibiaweb global amphibian assessment amphibian vocalisations on archival sound recordings amphibious organisms extant late devonian first appearances taxa

alaska (; ; ; ; yup'ik: alaskaq; ) is a state located in the western united states on the northwest extremity of north america. a semi-exclave of the u.s., it borders the canadian province of british columbia and the territory of yukon to the east and shares a maritime border with the russian federation's chukotka autonomous okrug to the west, just across the bering strait. to the north are the chukchi and beaufort seas of the arctic ocean, while the pacific ocean lies to the south and southwest. alaska is by far the largest u.s. state by area, comprising more total area than the next three largest states (texas, california, and montana) combined. it represents the seventh largest subnational division in the world. it is the third-least populous and the most sparsely populated state, but by far the continent's

most populous territory located mostly north of the 60th parallel, with a population of 736,081 as of 2020more than quadruple the combined populations of northern canada and greenland. approximately half of alaska's residents live within the anchorage metropolitan area. the state capital of juneau is the second-largest city in the united states by area, comprising more territory than the states of rhode island and delaware. the former capital of alaska, sitka, is the largest u.s. city by area. alaska was occupied by various indigenous peoples for thousands of years before the arrival of europeans. the state is considered the entry point for the settlement of north america by way of the bering land bridge. the russians were the first europeans to settle the area beginning in the 18th century, eventually establishing

russian america, which spanned most of the current state. the expense and difficulty of maintaining this distant possession prompted its sale to the u.s. in 1867 for us$7.2 million (equivalent to $ million in ), or approximately two cents per acre ($4.74/km2). the area went through several administrative changes before becoming organized as a territory on may 11, 1912. it was admitted as the 49th state of the u.s. on january 3, 1959. while it has one of the smallest state economies in the country, alaska's per capita income is among the highest, owing to a diversified economy dominated by fishing, natural gas, and oil, all of which it has in abundance. united states armed forces bases and tourism are also a significant part of the economy; more than half the state is federally owned public land, including a

multitude of national forests, national parks, and wildlife refuges. the indigenous population of alaska is proportionally the highest of any u.s. state, at over 15 percent. close to two dozen native languages are spoken, and alaskan natives exercise considerable influence in local and state politics. etymology the name "alaska" () was introduced in the russian colonial period when it was used to refer to the alaska peninsula. it was derived from an aleut-language idiom, "alaxsxaq", meaning "the mainland" or, more literally, "the object towards which the action of the sea is directed". it is also known as "alyeska", the "great land", an aleut word derived from the same root. history pre-colonization numerous indigenous peoples occupied alaska for thousands of years before the arrival of european peoples

to the area. linguistic and dna studies done here have provided evidence for the settlement of north america by way of the bering land bridge. at the upward sun river site in the tanana valley in alaska, remains of a six-week-old infant were found. the baby's dna showed that she belonged to a population that was genetically separate from other native groups present elsewhere in the new world at the end of the pleistocene. ben potter, the university of alaska fairbanks archaeologist who unearthed the remains at the upward sun river site in 2013, named this new group ancient beringians. the tlingit people developed a society with a matrilineal kinship system of property inheritance and descent in what is today southeast alaska, along with parts of british columbia and the yukon. also in southeast were the haida,

now well known for their unique arts. the tsimshian people came to alaska from british columbia in 1887, when president grover cleveland, and later the u.s. congress, granted them permission to settle on annette island and found the town of metlakatla. all three of these peoples, as well as other indigenous peoples of the pacific northwest coast, experienced smallpox outbreaks from the late 18th through the mid-19th century, with the most devastating epidemics occurring in the 1830s and 1860s, resulting in high fatalities and social disruption. the aleutian islands are still home to the aleut people's seafaring society, although they were the first native alaskans to be exploited by the russians. western and southwestern alaska are home to the yup'ik, while their cousins the alutiiq ~ sugpiaq live in what is

now southcentral alaska. the gwich'in people of the northern interior region are athabaskan and primarily known today for their dependence on the caribou within the much-contested arctic national wildlife refuge. the north slope and little diomede island are occupied by the widespread inupiat people. colonization some researchers believe the first russian settlement in alaska was established in the 17th century. according to this hypothesis, in 1648 several koches of semyon dezhnyov's expedition came ashore in alaska by storm and founded this settlement. this hypothesis is based on the testimony of chukchi geographer nikolai daurkin, who had visited alaska in 17641765 and who had reported on a village on the kheuveren river, populated by "bearded men" who "pray to the icons". some modern researchers associate

kheuveren with koyuk river. the first european vessel to reach alaska is generally held to be the st. gabriel under the authority of the surveyor m. s. gvozdev and assistant navigator i. fyodorov on august 21, 1732, during an expedition of siberian cossack a. f. shestakov and russian explorer dmitry pavlutsky (17291735). another european contact with alaska occurred in 1741, when vitus bering led an expedition for the russian navy aboard the st. peter. after his crew returned to russia with sea otter pelts judged to be the finest fur in the world, small associations of fur traders began to sail from the shores of siberia toward the aleutian islands. the first permanent european settlement was founded in 1784. between 1774 and 1800, spain sent several expeditions to alaska to assert its claim over the pacific

northwest. in 1789, a spanish settlement and fort were built in nootka sound. these expeditions gave names to places such as valdez, bucareli sound, and cordova. later, the russian-american company carried out an expanded colonization program during the early-to-mid-19th century. sitka, renamed new archangel from 1804 to 1867, on baranof island in the alexander archipelago in what is now southeast alaska, became the capital of russian america. it remained the capital after the colony was transferred to the united states. the russians never fully colonized alaska, and the colony was never very profitable. evidence of russian settlement in names and churches survive throughout southeastern alaska. william h. seward, the 24th united states secretary of state, negotiated the alaska purchase (also known as seward's

folly) with the russians in 1867 for $7.2 million. russia's contemporary ruler tsar alexander ii, the emperor of the russian empire, king of poland and grand duke of finland, also planned the sale; the purchase was made on march 30, 1867. six months later the commissioners arrived in sitka and the formal transfer was arranged; the formal flag-raising took place at fort sitka on october 18, 1867. in the ceremony 250 uniformed u.s. soldiers marched to the governor's house at "castle hill", where the russian troops lowered the russian flag and the u.s. flag was raised. this event is celebrated as alaska day, a legal holiday on october 18. alaska was loosely governed by the military initially, and was administered as a district starting in 1884, with a governor appointed by the united states president. a federal

district court was headquartered in sitka. for most of alaska's first decade under the united states flag, sitka was the only community inhabited by american settlers. they organized a "provisional city government", which was alaska's first municipal government, but not in a legal sense. legislation allowing alaskan communities to legally incorporate as cities did not come about until 1900, and home rule for cities was extremely limited or unavailable until statehood took effect in 1959. alaska as an incorporated u.s. territory starting in the 1890s and stretching in some places to the early 1910s, gold rushes in alaska and the nearby yukon territory brought thousands of miners and settlers to alaska. alaska was officially incorporated as an organized territory in 1912. alaska's capital, which had been in sitka

until 1906, was moved north to juneau. construction of the alaska governor's mansion began that same year. european immigrants from norway and sweden also settled in southeast alaska, where they entered the fishing and logging industries. during world war ii, the aleutian islands campaign focused on attu, agattu and kiska, all which were occupied by the empire of japan. during the japanese occupation, a white american civilian and two united states navy personnel were killed at attu and kiska respectively, and nearly a total of 50 aleut civilians and eight sailors were interned in japan. about half of the aleuts died during the period of internment. unalaska/dutch harbor and adak became significant bases for the united states army, united states army air forces and united states navy. the united states lend-lease

program involved flying american warplanes through canada to fairbanks and then nome; soviet pilots took possession of these aircraft, ferrying them to fight the german invasion of the soviet union. the construction of military bases contributed to the population growth of some alaskan cities. statehood statehood for alaska was an important cause of james wickersham early in his tenure as a congressional delegate. decades later, the statehood movement gained its first real momentum following a territorial referendum in 1946. the alaska statehood committee and alaska's constitutional convention would soon follow. statehood supporters also found themselves fighting major battles against political foes, mostly in the u.s. congress but also within alaska. statehood was approved by the u.s. congress on july 7, 1958;

alaska was officially proclaimed a state on january 3, 1959. good friday earthquake on march 27, 1964, the massive good friday earthquake killed 133 people and destroyed several villages and portions of large coastal communities, mainly by the resultant tsunamis and landslides. it was the second-most-powerful earthquake in recorded history, with a moment magnitude of 9.2 (more than a thousand times as powerful as the 1989 san francisco earthquake). the time of day (5:36 pm), time of year (spring) and location of the epicenter were all cited as factors in potentially sparing thousands of lives, particularly in anchorage. alaska oil boom the 1968 discovery of oil at prudhoe bay and the 1977 completion of the trans-alaska pipeline system led to an oil boom. royalty revenues from oil have funded large state budgets

from 1980 onward. that same year, not coincidentally, alaska repealed its state income tax. in 1989, the exxon valdez hit a reef in the prince william sound, spilling more than of crude oil over of coastline. today, the battle between philosophies of development and conservation is seen in the contentious debate over oil drilling in the arctic national wildlife refuge and the proposed pebble mine. geography located at the northwest corner of north america, alaska is the northernmost and westernmost state in the united states, but also has the most easterly longitude in the united states because the aleutian islands extend into the eastern hemisphere. alaska is the only non-contiguous u.s. state on continental north america; about of british columbia (canada) separates alaska from washington. it is technically

part of the continental u.s., but is sometimes not included in colloquial use; alaska is not part of the contiguous u.s., often called "the lower 48". the capital city, juneau, is situated on the mainland of the north american continent but is not connected by road to the rest of the north american highway system. the state is bordered by canada's yukon and british columbia to the east (making it the only state to border a canadian territory); the gulf of alaska and the pacific ocean to the south and southwest; the bering sea, bering strait, and chukchi sea to the west; and the arctic ocean to the north. alaska's territorial waters touch russia's territorial waters in the bering strait, as the russian big diomede island and alaskan little diomede island are only apart. alaska has a longer coastline than all

the other u.s. states combined. at in area, alaska is by far the largest state in the united states, and is more than twice the size of the second-largest u.s. state, texas. alaska is the seventh largest subnational division in the world, and if it was an independent nation would be the 16th largest country in the world, as it is larger than iran. with its myriad islands, alaska has nearly of tidal shoreline. the aleutian islands chain extends west from the southern tip of the alaska peninsula. many active volcanoes are found in the aleutians and in coastal regions. unimak island, for example, is home to mount shishaldin, which is an occasionally smoldering volcano that rises to above the north pacific. the chain of volcanoes extends to mount spurr, west of anchorage on the mainland. geologists have identified

alaska as part of wrangellia, a large region consisting of multiple states and canadian provinces in the pacific northwest, which is actively undergoing continent building. one of the world's largest tides occurs in turnagain arm, just south of anchorage, where tidal differences can be more than . alaska has more than three million lakes. marshlands and wetland permafrost cover (mostly in northern, western and southwest flatlands). glacier ice covers about of alaska. the bering glacier is the largest glacier in north america, covering alone. regions there are no officially defined borders demarcating the various regions of alaska, but there are six widely accepted regions: south central the most populous region of alaska, containing anchorage, the matanuska-susitna valley and the kenai peninsula. rural,

mostly unpopulated areas south of the alaska range and west of the wrangell mountains also fall within the definition of south central, as do the prince william sound area and the communities of cordova and valdez. southeast also referred to as the panhandle or inside passage, this is the region of alaska closest to the contiguous states. as such, this was where most of the initial non-indigenous settlement occurred in the years following the alaska purchase. the region is dominated by the alexander archipelago as well as the tongass national forest, the largest national forest in the united states. it contains the state capital juneau, the former capital sitka, and ketchikan, at one time alaska's largest city. the alaska marine highway provides a vital surface transportation link throughout the area and country,

as only three communities (haines, hyder and skagway) enjoy direct connections to the contiguous north american road system. interior the interior is the largest region of alaska; much of it is uninhabited wilderness. fairbanks is the only large city in the region. denali national park and preserve is located here. denali, formerly mount mckinley, is the highest mountain in north america, and is also located here. southwest southwest alaska is a sparsely inhabited region stretching some inland from the bering sea. most of the population lives along the coast. kodiak island is also located in southwest. the massive yukonkuskokwim delta, one of the largest river deltas in the world, is here. portions of the alaska peninsula are considered part of southwest, with the remaining portions included with the aleutian

islands (see below). north slope the north slope is mostly tundra peppered with small villages. the area is known for its massive reserves of crude oil and contains both the national petroleum reservealaska and the prudhoe bay oil field. the city of utqiagvik, formerly known as barrow, is the northernmost city in the united states and is located here. the northwest arctic area, anchored by kotzebue and also containing the kobuk river valley, is often regarded as being part of this region. however, the respective inupiat of the north slope and of the northwest arctic seldom consider themselves to be one people. aleutian islands more than 300 small volcanic islands make up this chain, which stretches more than into the pacific ocean. some of these islands fall in the eastern hemisphere, but the international

date line was drawn west of 180 to keep the whole state, and thus the entire north american continent, within the same legal day. two of the islands, attu and kiska, were occupied by japanese forces during world war ii. land ownership according to an october 1998 report by the united states bureau of land management, approximately 65% of alaska is owned and managed by the u.s. federal government as public lands, including a multitude of national forests, national parks, and national wildlife refuges. of these, the bureau of land management manages , or 23.8% of the state. the arctic national wildlife refuge is managed by the united states fish and wildlife service. it is the world's largest wildlife refuge, comprising . of the remaining land area, the state of alaska owns , its entitlement under the alaska

statehood act. a portion of that acreage is occasionally ceded to the organized boroughs presented above, under the statutory provisions pertaining to newly formed boroughs. smaller portions are set aside for rural subdivisions and other homesteading-related opportunities. these are not very popular due to the often remote and roadless locations. the university of alaska, as a land grant university, also owns substantial acreage which it manages independently. another are owned by 12 regional, and scores of local, native corporations created under the alaska native claims settlement act (ancsa) of 1971. regional native corporation doyon, limited often promotes itself as the largest private landowner in alaska in advertisements and other communications. provisions of ancsa allowing the corporations' land holdings

to be sold on the open market starting in 1991 were repealed before they could take effect. effectively, the corporations hold title (including subsurface title in many cases, a privilege denied to individual alaskans) but cannot sell the land. individual native allotments can be and are sold on the open market, however. various private interests own the remaining land, totaling about one percent of the state. alaska is, by a large margin, the state with the smallest percentage of private land ownership when native corporation holdings are excluded. alaska heritage resources survey the alaska heritage resources survey (ahrs) is a restricted inventory of all reported historic and prehistoric sites within the u.s. state of alaska; it is maintained by the office of history and archaeology. the survey's inventory

of cultural resources includes objects, structures, buildings, sites, districts, and travel ways, with a general provision that they are more than fifty years old. , more than 35,000 sites have been reported. cities, towns and boroughs alaska is not divided into counties, as most of the other u.s. states, but it is divided into boroughs. delegates to the alaska constitutional convention wanted to avoid the pitfalls of the traditional county system and adopted their own unique model. many of the more densely populated parts of the state are part of alaska's 16 boroughs, which function somewhat similarly to counties in other states. however, unlike county-equivalents in the other 49 states, the boroughs do not cover the entire land area of the state. the area not part of any borough is referred to as the unorganized

borough. the unorganized borough has no government of its own, but the u.s. census bureau in cooperation with the state divided the unorganized borough into 11 census areas solely for the purposes of statistical analysis and presentation. a recording district is a mechanism for management of the public record in alaska. the state is divided into 34 recording districts which are centrally administered under a state recorder. all recording districts use the same acceptance criteria, fee schedule, etc., for accepting documents into the public record. whereas many u.s. states use a three-tiered system of decentralizationstate/county/townshipmost of alaska uses only two tiersstate/borough. owing to the low population density, most of the land is located in the unorganized borough. as the name implies, it has no

intermediate borough government but is administered directly by the state government. in 2000, 57.71% of alaska's area has this status, with 13.05% of the population. anchorage merged the city government with the greater anchorage area borough in 1975 to form the municipality of anchorage, containing the city proper and the communities of eagle river, chugiak, peters creek, girdwood, bird, and indian. fairbanks has a separate borough (the fairbanks north star borough) and municipality (the city of fairbanks). the state's most populous city is anchorage, home to 291,247 people in 2020. the richest location in alaska by per capita income is denali ($42,245). yakutat city, sitka, juneau, and anchorage are the four largest cities in the u.s. by area. cities and census-designated places (by population) as reflected

in the 2020 united states census, alaska has a total of 355 incorporated cities and census-designated places (cdps). the tally of cities includes four unified municipalities, essentially the equivalent of a consolidated citycounty. the majority of these communities are located in the rural expanse of alaska known as "the bush" and are unconnected to the contiguous north american road network. the table at the bottom of this section lists the 100 largest cities and census-designated places in alaska, in population order. of alaska's 2020 u.s. census population figure of 733,391, 16,655 people, or 2.27% of the population, did not live in an incorporated city or census-designated place. approximately three-quarters of that figure were people who live in urban and suburban neighborhoods on the outskirts of the city

limits of ketchikan, kodiak, palmer and wasilla. cdps have not been established for these areas by the united states census bureau, except that seven cdps were established for the ketchikan-area neighborhoods in the 1980 census (clover pass, herring cove, ketchikan east, mountain point, north tongass highway, pennock island and saxman east), but have not been used since. the remaining population was scattered throughout alaska, both within organized boroughs and in the unorganized borough, in largely remote areas. climate the climate in south and southeastern alaska is a mid-latitude oceanic climate (koppen climate classification: cfb), and a subarctic oceanic climate (koppen cfc) in the northern parts. on an annual basis, the southeast is both the wettest and warmest part of alaska with milder temperatures

in the winter and high precipitation throughout the year. juneau averages over of precipitation a year, and ketchikan averages over . this is also the only region in alaska in which the average daytime high temperature is above freezing during the winter months.the climate of anchorage and south central alaska is mild by alaskan standards due to the region's proximity to the seacoast. while the area gets less rain than southeast alaska, it gets more snow, and days tend to be clearer. on average, anchorage receives of precipitation a year, with around of snow, although there are areas in the south central which receive far more snow. it is a subarctic climate (koppen: dfc) due to its brief, cool summers. the climate of western alaska is determined in large part by the bering sea and the gulf of alaska. it is

a subarctic oceanic climate in the southwest and a continental subarctic climate farther north. the temperature is somewhat moderate considering how far north the area is. this region has a tremendous amount of variety in precipitation. an area stretching from the northern side of the seward peninsula to the kobuk river valley (i.e., the region around kotzebue sound) is technically a desert, with portions receiving less than of precipitation annually. on the other extreme, some locations between dillingham and bethel average around of precipitation. the climate of the interior of alaska is subarctic. some of the highest and lowest temperatures in alaska occur around the area near fairbanks. the summers may have temperatures reaching into the 90s f (the low-to-mid 30s c), while in the winter, the temperature

can fall below . precipitation is sparse in the interior, often less than a year, but what precipitation falls in the winter tends to stay the entire winter. the highest and lowest recorded temperatures in alaska are both in the interior. the highest is in fort yukon (which is just inside the arctic circle) on june 27, 1915, making alaska tied with hawaii as the state with the lowest high temperature in the united states. the lowest official alaska temperature is in prospect creek on january 23, 1971, one degree above the lowest temperature recorded in continental north america (in snag, yukon, canada). the climate in the extreme north of alaska is arctic (koppen: et) with long, very cold winters and short, cool summers. even in july, the average low temperature in utqiagvik is . precipitation is light in this

part of alaska, with many places averaging less than per year, mostly as snow which stays on the ground almost the entire year. demographics the united states census bureau found in the 2020 united states census that the population of alaska was 736,081 on april 1, 2020, a 3.6% increase since the 2010 united states census. according to the 2010 united states census, the u.s. state of alaska had a population of 710,231, increasing from 626,932 at the 2000 u.s. census. in 2010, alaska ranked as the 47th state by population, ahead of north dakota, vermont, and wyoming (and washington, d.c.). estimates show north dakota ahead . alaska is the least densely populated state, and one of the most sparsely populated areas in the world, at , with the next state, wyoming, at . alaska is by far the largest u.s. state by

area, and the tenth wealthiest (per capita income). due to its population size, it is one of 14 u.s. states that still have only one telephone area code. race and ethnicity the 2019 american community survey estimated 60.2% of the population was non-hispanic white, 3.7% black or african american, 15.6% american indian or alaska native, 6.5% asian, 1.4% native hawaiian and other pacific islander, 7.5% two or more races, and 7.3% hispanic or latin american of any race. at the survey estimates, 7.8% of the total population was foreign-born from 2015 to 2019. in 2015, 61.3% was non-hispanic white, 3.4% black or african american, 13.3% american indian or alaska native, 6.2% asian, 0.9% native hawaiian and other pacific islander, 0.3% some other race, and 7.7% multiracial. hispanics and latin americans were 7% of

the state population in 2015. from 2015 to 2019, the largest hispanic and latin american groups were mexican americans, puerto ricans, and cuban americans. the largest asian groups living in the state were filipinos, korean americans, and japanese and chinese americans. the state was 66.7% white (64.1% non-hispanic white), 14.8% american indian and alaska native, 5.4% asian, 3.3% black or african american, 1.0% native hawaiian and other pacific islander, 1.6% from some other race, and 7.3% from two or more races in 2010. hispanics or latin americans of any race made up 5.5% of the population in 2010. , 50.7% of alaska's population younger than one year of age belonged to minority groups (i.e., did not have two parents of non-hispanic white ancestry). in 1960, the united states census bureau reported alaska's

population as 77.2% white, 3% black, and 18.8% american indian and alaska native. languages according to the 2011 american community survey, 83.4% of people over the age of five spoke only english at home. about 3.5% spoke spanish at home, 2.2% spoke another indo-european language, about 4.3% spoke an asian language (including tagalog), and about 5.3% spoke other languages at home. in 2019, the american community survey determined 83.7% spoke only english, and 16.3% spoke another language other than english. the most spoken european language after english was spanish, spoken by approximately 4.0% of the state population. collectively, asian and pacific islander languages were spoken by 5.6% of alaskans. since 2010, a total of 5.2% of alaskans speak one of the state's 20 indigenous languages, known locally as

"native languages". the alaska native language center at the university of alaska fairbanks claims that at least 20 alaskan native languages exist and there are also some languages with different dialects. most of alaska's native languages belong to either the eskimoaleut or na-dene language families; however, some languages are thought to be isolates (e.g. haida) or have not yet been classified (e.g. tsimshianic). nearly all of alaska's native languages were classified as either threatened, shifting, moribund, nearly extinct, or dormant languages. in october 2014, the governor of alaska signed a bill declaring the state's 20 indigenous languages to have official status. this bill gave them symbolic recognition as official languages, though they have not been adopted for official use within the government.

the 20 languages that were included in the bill are: inupiaq siberian yupik central alaskan yup'ik alutiiq unangax dena'ina deg xinag holikachuk koyukon upper kuskokwim gwich'in tanana upper tanana tanacross han ahtna eyak tlingit haida tsimshian religion according to statistics collected by the association of religion data archives from 2010, about 34% of alaska residents were members of religious congregations. of the religious population, 100,960 people identified as evangelical protestants; 50,866 as roman catholic; and 32,550 as mainline protestants. roughly 4% were mormon, 0.5% jewish, 0.5% muslim, 1% buddhist, 0.2% bahai, and 0.5% hindu. the largest religious denominations in alaska was the catholic church with 50,866 adherents; non-denominational evangelicals with 38,070 adherents;

the church of jesus christ of latter-day saints with 32,170 adherents; and the southern baptist convention with 19,891 adherents. alaska has been identified, along with pacific northwest states washington and oregon, as being the least religious states of the usa, in terms of church membership. the pew research center in 2014 determined 62% of the adult population practiced christianity. protestantism was the largest christian tradition, dominated by evangelicalism. mainline protestants were the second largest protestant christian group, followed by predominantly african american churches. the catholic church remained the largest single christian tradition practiced in alaska. of the unaffiliated population, they made up the largest non-christian religious affiliation. atheists made up 5% of the population and

the largest non-christian religion was buddhism. in 1795, the first russian orthodox church was established in kodiak. intermarriage with alaskan natives helped the russian immigrants integrate into society. as a result, an increasing number of russian orthodox churches gradually became established within alaska. alaska also has the largest quaker population (by percentage) of any state. in 2009, there were 6,000 jews in alaska (for whom observance of halakha may pose special problems). alaskan hindus often share venues and celebrations with members of other asian religious communities, including sikhs and jains. in 2010, alaskan hindus established the sri ganesha temple of alaska, making it the first hindu temple in alaska and the northernmost hindu temple in the world. there are an estimated 2,0003,000 hindus

in alaska. the vast majority of hindus live in anchorage or fairbanks. estimates for the number of muslims in alaska range from 2,000 to 5,000. the islamic community center of anchorage began efforts in the late 1990s to construct a mosque in anchorage. they broke ground on a building in south anchorage in 2010 and were nearing completion in late 2014. when completed, the mosque will be the first in the state and one of the northernmost mosques in the world. there's also a bahai center. economy as of 2016, alaska had a total employment of 266,072. the number of employer establishments was 21,077. the 2018 gross state product was $55 billion, 48th in the u.s.. its per capita personal income for 2018 was $73,000, ranking 7th in the nation. according to a 2013 study by phoenix marketing international, alaska

had the fifth-largest number of millionaires per capita in the united states, with a ratio of 6.75 percent. the oil and gas industry dominates the alaskan economy, with more than 80% of the state's revenues derived from petroleum extraction. alaska's main export product (excluding oil and natural gas) is seafood, primarily salmon, cod, pollock and crab. agriculture represents a very small fraction of the alaskan economy. agricultural production is primarily for consumption within the state and includes nursery stock, dairy products, vegetables, and livestock. manufacturing is limited, with most foodstuffs and general goods imported from elsewhere. employment is primarily in government and industries such as natural resource extraction, shipping, and transportation. military bases are a significant component

of the economy in the fairbanks north star, anchorage and kodiak island boroughs, as well as kodiak. federal subsidies are also an important part of the economy, allowing the state to keep taxes low. its industrial outputs are crude petroleum, natural gas, coal, gold, precious metals, zinc and other mining, seafood processing, timber and wood products. there is also a growing service and tourism sector. tourists have contributed to the economy by supporting local lodging. energy alaska has vast energy resources, although its oil reserves have been largely depleted. major oil and gas reserves were found in the alaska north slope (ans) and cook inlet basins, but according to the energy information administration, by february 2014 alaska had fallen to fourth place in the nation in crude oil production after texas,

north dakota, and california. prudhoe bay on alaska's north slope is still the second highest-yielding oil field in the united states, typically producing about , although by early 2014 north dakota's bakken formation was producing over . prudhoe bay was the largest conventional oil field ever discovered in north america, but was much smaller than canada's enormous athabasca oil sands field, which by 2014 was producing about of unconventional oil, and had hundreds of years of producible reserves at that rate. the trans-alaska pipeline can transport and pump up to of crude oil per day, more than any other crude oil pipeline in the united states. additionally, substantial coal deposits are found in alaska's bituminous, sub-bituminous, and lignite coal basins. the united states geological survey estimates that