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|White's Tree Frog (Litoria caerulea)|
White's Tree Frog (Litoria caerulea)
|Distribution of frogs (in black)|
Distribution of frogs (in black)
The frog is an amphibian in the order Anura (meaning "tail-less", from Greek an-, without + oura, tail), formerly referred to as Salientia (Latin saltare, to jump). The name frog derives from Old English frogga, (compare Old Norse frauki, German Frosch, older Dutch spelling kikvorsch), cognate with Sanskrit plava (frog), probably deriving from Proto-Indo-European praw = "to jump".
Adult frogs are characterised by long hind legs, a short body, webbed digits, protruding eyes and the absence of a tail. Most frogs have a semi-aquatic lifestyle, but move easily on land by jumping or climbing. They typically lay their eggs in puddles, ponds or lakes, and their larvae, called tadpoles, have gills and develop in water. Adult frogs follow a carnivorous diet, mostly of arthropods, annelids and gastropods. Frogs are most noticeable by their call, which can be widely heard during the night or day, mainly in their mating season.
The distribution of frogs ranges from tropic to subarctic regions, but most species are found in tropical rainforests. Consisting of more than 5,000 species described, they are among the most diverse groups of vertebrates. However, populations of certain frog species are significantly declining.
A distinction is often made between frogs and toads on the basis of their appearance, caused by the convergent adaptation among so-called toads to dry environments; however, this distinction has no taxonomic basis. The only family exclusively given the common name "toad" is Bufonidae, but many species from other families are also called "toads," and the species within the toad genus Atelopus are referred to as "harlequin frogs."
- 1 Taxonomy
- 2 Morphology and physiology
- 3 Natural history
- 4 Distribution and conservation status
- 5 Evolution
- 6 Uses in agriculture and research
- 7 Cultural beliefs
- 8 Cited references
- 9 Futher reading
- 10 External links
- For more details on this topic, see List of Anuran families.
The order Anura contains 5,250 species in 33 families, of which the Leptodactylidae (1100 spp.), Hylidae (800 spp.) and Ranidae (750 spp.) are the richest in species. About 88% of amphibian species are frogs.
The use of the common names "frog" and "toad" has no taxonomic justification. From a taxonomic perspective, all members of the order Anura are frogs, but only members of the family Bufonidae are considered "true toads". The use of the term "frog" in common names usually refers to species that are aquatic or semi-aquatic with smooth and/or moist skins, and the term "toad" generally refers to species that tend to be terrestrial with dry, warty skin. An exception is the fire-bellied toad (Bombina bombina): while its skin is slightly warty, it prefers a watery habitat.
Frogs and toads are broadly classified into three suborders: Archaeobatrachia, which includes four families of primitive frogs; Mesobatrachia, which includes five families of more evolutionary intermediate frogs; and Neobatrachia, by far the largest group, which contains the remaining 24 families of "modern" frogs, including most common species throughout the world. Neobatrachia is further divided into the Hyloidea and Ranoidea. This classification is based on such morphological features as the number of vertebrae, the structure of the pectoral girdle, and the morphology of tadpoles. While this classification is largely accepted, relationships among families of frogs are still debated. Future studies of molecular genetics should soon provide further insights to the evolutionary relationships among frog families.
Some species of anurans hybridise readily. For instance, the edible frog (Rana esculenta) is a hybrid of the pool frog (R. lessonae) and the marsh frog (R. ridibunda). Bombina bombina and Bombina variegata similarly form hybrids, although these are less fertile, giving rise to a hybrid zone.
Morphology and physiology
- For more details on this topic, see Frog zoology.
The morphology of frogs is unique among amphibians. Compared with the other two groups of amphibians, (salamanders and caecilians), frogs are unusual because they lack tails as adults and their legs are more suited to jumping than walking. The physiology of frogs is generally like that of other amphibians (and differs from other terrestrial vertebrates) because oxygen can pass through their highly permeable skin. This unique feature allows frogs to "breathe" largely through their skin. Because the oxygen is dissolved in an aqueous film on the skin and passes from there to the blood, the skin must remain moist at all times; this makes frogs susceptible to many toxins in the environment, some of which can similarly dissolve in the layer of water and be passed into their bloodstream. This may be cause of the decline in frog populations.
Many characteristics are not shared by all of the approximately 5,250 described frog species. However, some general characteristics distinguish them from other amphibians. Frogs are usually well suited to jumping, with long hind legs and elongated ankle bones. They have a short vertebral column, with no more than ten free vertebrae, followed by a fused tailbone (urostyle or coccyx), typically resulting in a tailless phenotype.
Frogs range in size from 10 mm (Brachycephalus didactylus of Brazil and Eleutherodactylus iberia of Cuba) to 300 mm (goliath frog, Conraua goliath, of Cameroon). The skin hangs loosely on the body because of the lack of loose connective tissue. Skin texture varies: it can be smooth, warty or folded. Frogs have three eyelid membranes: one is transparent to protect the eyes underwater, and two vary from translucent to opaque. Frogs have a tympanum on each side of the head, which is involved in hearing and, in some species, is covered by skin. Most frogs do in fact have teeth of a sort. They have a ridge of very small cone teeth around the upper edge of the jaw. These are called maxillary teeth. Frogs often also have what are called vomerine teeth on the roof of their mouth. They do not have anything that could be called teeth on their lower jaw, so they usually swallow their food whole. The so-called "teeth" are mainly used to hold the prey and keep it in place till they can get a good grip on it and squash their eyeballs down to swallow their meal. Toads, however, do not have any teeth.
Feet and legs
The structure of the feet and legs varies greatly among frog species, depending in part on whether they live primarily on the ground, in water, in trees, or in burrows. Frogs must be able to move quickly through their environment to catch prey and escape predators, and numerous adaptations help them do so.
Many frogs, especially those that live in water, have webbed toes. The degree to which the toes are webbed is directly proportional to the amount of time the species lives in the water. For example, the completely aquatic African dwarf frog (Hymenochirus sp.) has fully webbed toes, whereas the toes of White's tree frog (Litoria caerulea), an arboreal species, are only a half or a quarter webbed.
Arboreal frogs have "toe pads" to help grip vertical surfaces. These pads, located on the ends of the toes, do not work by suction. Rather, the surface of the pad consists of interlocking cells, with a small gap between adjacent cells. When the frog applies pressure to the toe pads, the interlocking cells grip irregularities on the substrate. The small gaps between the cells drain away all but a thin layer of moisture on the pad, and maintain a grip through capillarity. This allows the frog to grip smooth surfaces, and does not function when the pads are excessively wet.
In many arboreal frogs, a small "intercalary structure" in each toe increases the surface area touching the substrate. Furthermore, since hopping through trees can be dangerous, many arboreal frogs have hip joints that allow both hopping and walking. Some frogs that live high in trees even possess an elaborate degree of webbing between their toes, as do aquatic frogs. In these arboreal frogs, the webs allow the frogs to "parachute" or control their glide from one position in the canopy to another.
Ground-dwelling frogs generally lack the adaptations of aquatic and arboreal frogs. Most have smaller toe pads, if any, and little webbing. Some burrowing frogs have a toe extension—a metatarsal tubercle—that helps them to burrow. The hind legs of ground dwellers are more muscular than those of aqueous and tree-dwelling frogs.
While frog species can use a variety of locomotor modes (running, walking, gliding, swimming and climbing), more are either proficient at jumping or descended from ancestors who were, with much of the musculo-skeletal morphology modified for this purpose. The tibia, fibula and tarsals have been fused into a single, strong bone, as have the radius and ulna in the forelimbs (which must absorb the impact of landing). The metatarsals have become elongated to add to the leg length and allow the frog to push against the ground for longer during a jump. The illium has elongated and formed a mobile joint with the sacrum which, in specialist jumpers such as Ranids or Hylids, functions as an additional limb joint to further power the leaps.
Many frogs are able to absorb water directly through the skin, especially around the pelvic area. However, the permeability of a frog's skin can also result in water loss. Some tree frogs reduce water loss with a waterproof layer of skin. Others have adapted behaviours to conserve water, including engaging in nocturnal activity and resting in a water-conserving position. This position involves the frog lying with its toes and fingers tucked under its body and chin, respectively, with no gap between the body and substrate. Some frog species will also rest in large groups, touching the skin of the neighbouring frog. This reduces the amount of skin exposed to the air or a dry surface, and thus reduces water loss. These adaptations only reduce water loss enough for a predominantly arboreal existence, and are not suitable for arid conditions.
Camouflage is a common defensive mechanism in frogs. Most camouflaged frogs are nocturnal, which adds to their ability to hide. Nocturnal frogs usually find the ideal camouflaged position during the day to sleep. Some frogs have the ability to change colour, but this is usually restricted to shades of one or two colours. For example, White's tree frog varies in shades of green and brown. Features such as warts and skin folds are usually found on ground-dwelling frogs, where a smooth skin would not disguise them effectively. Arboreal frogs usually have smooth skin, enabling them to disguise themselves as leaves.
Certain frogs change colour between night and day, as light and moisture stimulate the pigment cells and cause them to expand or contract.
Many frogs contain mild toxins that make them unpalatable to potential predators. For example, all toads have large poison glands—the parotid glands—located behind the eyes on the top of the head. Some frogs, such as some poison dart frogs, are especially toxic. The chemical makeup of toxins in frogs varies from irritants to hallucinogens, convulsants, nerve poisons, and vasoconstrictors. Many predators of frogs have adapted to tolerate high levels of these poisons. Others, including humans, may be severely affected.
Some frogs obtain poisons from the ants and other arthropods they eat; others, such as the Australian Corroboree Frogs (Pseudophryne corroboree and Pseudophryne pengilleyi), can manufacture an alkaloid not derived from their diet. Some native people of South America extract poison from the poison dart frogs and apply it to their darts for hunting, although few species are toxic enough to be used for this purpose. It was previously a misconception the poison was placed on arrows rather than darts. The common name of these frogs was thus changed from "poison arrow frog" to "poison dart frog" in the early 1980s. Poisonous frogs tend to advertise their toxicity with bright colours, an adaptive strategy known as aposematism. There are at least two non-poisonous species of frogs in tropical America (Eleutherodactylus gaigei and Lithodytes lineatus) that mimic the colouration of dart poison frogs' coloration for self-protection (Batesian mimicry).
Because frog toxins are extraordinarily diverse, they have raised the interest of biochemists as a "natural pharmacy". The alkaloid epibatidine, a painkiller 200 times more potent than morphine, is found in some species of poison dart frogs. Other chemicals isolated from the skin of frogs may offer resistance to HIV infection. Arrow and dart poisons are under active investigation for their potential as therapeutic drugs.
The skin secretions of some toads, such as the Colorado River toad and cane toad, contain bufotoxins, some of which, such as bufotenin, are psychoactive, and have therefore been used as recreational drugs. Typically, the skin secretions are dried and smoked. Skin licking is especially dangerous, and appears to constitute an urban myth. See psychoactive toad.
Respiration and circulation
The skin of a frog is permeable to oxygen and carbon dioxide, as well as to water. There are a number of blood vessels near the surface of the skin. When a frog is underwater, oxygen is transmitted through the skin directly into the bloodstream. On land, adult frogs use their lungs to breathe. Their lungs are similar to those of humans, but the chest muscles are not involved in respiration, and there are no ribs or diaphragm to support breathing. Frogs breathe by taking air in through the nostrils (causing the throat to puff out), and compressing the floor of the mouth, which forces the air into the lungs.
Frogs are known for their three-chambered heart, which they share with all tetrapods except birds and mammals. In the three-chambered heart, oxygenated blood from the lungs and de-oxygenated blood from the respiring tissues enter by separate atria, and are directed via a spiral valve to the appropriate vessel—aorta for oxygenated blood and pulmonary vein for deoxygenated blood. This special structure is essential to keeping the mixing of the two types of blood to a minimum, which enables frogs to have higher metabolic rates, and to be more active than otherwise.
The life cycle of frogs, like that of other amphibians, consists of four main stages: egg, tadpole, metamorphosis and adult. The reliance of frogs on an aquatic environment for the egg and tadpole stages gives rise to a variety of breeding behaviours that include the well-known mating calls used by the males of most species to attract females to the bodies of water that they have chosen for breeding. Some frogs also look after their eggs—and in some cases even the tadpoles—for some time after laying.
The life cycle of a frog starts with an egg. A female generally lays frogspawn, or egg masses containing thousands of eggs, in water. The eggs are highly vulnerable to predation, so frogs have evolved many techniques to ensure the survival of the next generation. Most commonly, this involves synchronous reproduction. Many individuals will breed at the same time, overwhelming the actions of predators; the majority of the offspring will still die due to predation, but there is a greater chance some will survive. Another way in which some species avoid the predators and pathogens eggs are exposed to in ponds is to lay eggs on leaves above the pond, with a gelatinous coating designed to retain moisture. In these species the tadpoles drop into the water upon hatching. The eggs of some species laid out of water can detect vibrations of nearby predatory wasps or snakes, and will hatch early to avoid being eaten. Some species, such as the Cane Toad (Bufo marinus), lay poisonous eggs to minimise predation. While the length of the egg stage depends on the species and environmental conditions, aquatic eggs generally hatch within one week.
Eggs hatch and continue life as tadpoles (occasionally known as polliwogs). Tadpoles are aquatic, lack front and hind legs, and have gills for respiration and tails with fins for swimming. Tadpoles are typically herbivorous, feeding mostly on algae, including diatoms filtered from the water through the gills. Some species are carnivorous at the tadpole stage, eating insects, smaller tadpoles, and fish. Tadpoles are highly vulnerable to predation by fish, newts, predatory diving beetles and birds such as kingfishers. Cannibalism has been observed among tadpoles. Poisonous tadpoles are present in many species, such as Cane Toads. The tadpole stage may be as short as a week, or tadpoles may overwinter and metamorphose the following year in some species, such as the midwife toad (Alytes obstetricans) and the common spadefoot (Pelobates fuscus).
At the end of the tadpole stage, frogs undergo metamorphosis, in which they transition into adult form. Metamorphosis involves a dramatic transformation of morphology and physiology, as tadpoles develop hind legs, then front legs, lose their gills and develop lungs. Their intestines shorten as they shift from an herbivorous to a carnivorous diet. Eyes migrate rostrally and dorsally, allowing for binocular vision exhibited by the adult frog. This shift in eye position mirrors the shift from prey to predator, as the tadpole develops and depends less upon a larger and wider field of vision and more upon depth perception. The final stage of development from froglet to adult frog involves apoptosis (programmed cell death) and resorption of the tail.
After metamorphosis, young adults may leave the water and disperse into terrestrial habitats, or continue to live in the aquatic habitat as adults. Almost all species of frogs are carnivorous as adults, eating invertebrates such as arthropods, annelids and gastropods. A few of the larger species may eat prey such as small mammals, fish and smaller frogs. Some frogs use their sticky tongues to catch fast-moving prey, while others capture their prey and force it into their mouths with their hands. However, there are a very few species of frogs that primarily eat plants. Adult frogs are themselves preyed upon by birds, large fish, snakes, otters, foxes, badgers, coatis, and other animals. Frogs are also eaten by people (see section on uses in agriculture and research, below).
Frogs and toads can live for many years though little is known about their life span in the wild captive frogs and toads are recorded living up to 40 years .
Although it is not common knowledge, some species of frog in their tadpole stage are known to be carnivorous. Early developers who gain legs may be eaten by the others, so the late bloomers survive longer. This has been observed in England in the species Rana temporaria (common frog).
Reproduction of frogs
Once adult frogs reach maturity, they will assemble at a water source such as a pond or stream to breed. Many frogs return to the bodies of water where they were born, often resulting in annual migrations involving thousands of frogs. In continental Europe, a large proportion of migrating frogs used to die on roads, before special fences and tunnels were built for them.
Once at the breeding ground, male frogs call to attract a mate, collectively becoming a chorus of frogs. The call is unique to the species, and will attract females of that species. Some species have satellite males who do not call, but intercept females that are approaching a calling male.
The male and female frogs then undergo amplexus. This involves the male mounting the female and gripping her tightly. Fertilization is external: the egg and sperm meet outside of the body. The female releases her eggs, which the male frog covers with a sperm solution. The eggs then swell and develop a protective coating. The eggs are typically brown or black, with a clear, gelatin-like covering.
Most temperate species of frogs reproduce between late autumn and early spring. In the UK, most common frog populations produce frogspawn in February, although there is wide variation in timing. Water temperatures at this time of year are relatively low, typically between four and 10 degrees Celsius. Reproducing in these conditions helps the developing tadpoles because dissolved oxygen concentrations in the water are highest at cold temperatures. More importantly, reproducing early in the season ensures that appropriate food is available to the developing frogs at the right time.
Although care of offspring is poorly understood in frogs, it is estimated that up to 20% of amphibian species may care for their young in one way or another, and there is a great diversity of parental behaviours. Some species of poison dart frog lay eggs on the forest floor and protect them, guarding the eggs from predation and keeping them moist. The frog will urinate on them if they become too dry. After hatching, a parent (the sex depends upon the species) will move them, on its back, to a water-holding bromeliad. The parent then feeds them by laying unfertilized eggs in the bromeliad until the young have metamorphosed. Other frogs carry the eggs and tadpoles on their hind legs or back (e.g. the midwife toads, Alytes spp.). Some frogs even protect their offspring inside their own bodies. The male Australian Pouched Frog (Assa darlingtoni) has pouches along its side in which the tadpoles reside until metamorphosis. The female Gastric-brooding Frogs (genus Rheobatrachus) from Australia, now probably extinct, swallows its tadpoles, which then develop in the stomach. To do this, the Gastric-brooding Frog must stop secreting stomach acid and suppress peristalsis (contractions of the stomach). Darwin's Frog (Rhinoderma darwinii) from Chile puts the tadpoles in its vocal sac for development. Some species of frog will leave a 'babysitter' to watch over the frogspawn until it hatches.
Some frog calls are so loud, they can be heard up to a mile away.The call of a frog is unique to its species. Frogs call by passing air through the larynx in the throat. In most calling frogs, the sound is amplified by one or more vocal sacs, membranes of skin under the throat or on the corner of the mouth that distend during the amplification of the call. The field of neuroethology studies the neurocircuitry that underlies frog audition.
Some frogs lack vocal sacs, such as those from the genera Heleioporus and Neobatrachus, but these species can still produce a loud call. Their buccal cavity is enlarged and dome-shaped, acting as a resonance chamber that amplifies their call. Species of frog without vocal sacs and that do not have a loud call tend to inhabit areas close to flowing water. The noise of flowing water overpowers any call, so they must communicate by other means.
The main reason for calling is to allow males to attract a mate. Males call either individually or in a group called a chorus. Females of many frog species, for example Polypedates leucomystax, produce calls reciprocal to the males', which act as the catalyst for the enhancement of reproductive activity in a breeding colony. A male frog emits a release call when mounted by another male. Tropical species also have a rain call that they make on the basis of humidity cues prior to a rain shower. Many species also have a territorial call that is used to chase away other males. All of these calls are emitted with the mouth of the frog closed.
A distress call, emitted by some frogs when they are in danger, is produced with the mouth open, resulting in a higher-pitched call. The effectiveness of the call is unknown; however, it is suspected the call intrigues the predator until another animal is attracted, distracting them enough for its escape.
Many species of frog have deep calls, or croaks. The onomatopoeic spelling is "ribbit". The croak of the American bullfrog (Rana catesbiana) is sometimes spelt "jug o' rum". Other examples are Ancient Greek brekekekex koax koax for probably Rana ridibunda, and the description in Rigveda 7:103.6 gómāyur éko ajámāyur ékaħ = "one [has] a voice like a cow's, one [has] a voice like a goat's".
Distribution and conservation status
The habitat of frogs extends almost worldwide, but they do not occur in Antarctica and are not present on many oceanic islands. The greatest diversity of frogs occurs in the tropical areas of the world, where water is readily available, suiting frogs' requirements due to their skin. Some frogs inhabit arid areas such as deserts, where water may not be easily accessible, and rely on specific adaptations to survive. The Australian genus Cyclorana and the American genus Pternohyla will bury themselves underground, create a water-impervious cocoon and hibernate during dry periods. Once it rains, they emerge, find a temporary pond and breed. Egg and tadpole development is very fast in comparison to most other frogs so that breeding is complete before the pond dries up. Some frog species are adapted to a cold environment; for instance the wood frog, whose habitat extends north of the Arctic Circle, buries itself in the ground during winter when much of its body freezes.
Frog populations have declined dramatically since the 1950s: more than one third of species are believed to be threatened with extinction and more than 120 species are suspected to be extinct since the 1980s. Among these species are the golden toad of Costa Rica and the Gastric-brooding frogs of Australia. Habitat loss is a significant cause of frog population decline, as are pollutants, climate change, the introduction of non-indigenous predators/competitors, and emerging infectious diseases including chytridiomycosis. Many environmental scientists believe that amphibians, including frogs, are excellent biological indicators of broader ecosystem health because of their intermediate position in food webs, permeable skins, and typically biphasic life (aquatic larvae and terrestrial adults).
A Canadian study conducted in 2006 proposed heavy traffic near frog habitats as a large threat to frog populations.
In a few cases, captive breeding programs have been attempted to alleviate the pressure on frog populations, and these have proved successful. In May 2007, it was reported the application of certain probiotic bacteria could protect amphibians from chytridiomycosis.
The earliest known (proto) frog is Triadobatrachus massinoti, from the 250 million year old early Triassic of Madagascar. The skull is frog-like, being broad with large eye sockets, but the fossil has features diverging from modern amphibia. These include a different ilium, a longer body with more vertebrae, and separate vertebrae in its tail (whereas in modern frogs, the tail vertebrae are fused, and known as the urostyle or coccyx). The tibia and fibula bones are unfused and separate, making it probable Triadobatrachus was not an efficient leaper.
Another fossil frog, discovered in Arizona and called Prosalirus bitis, was uncovered in 1985, and dates from roughly the same time as Triadobatrachus. Like Triadobatrachus, Prosalirus did not have greatly enlarged legs, but had the typical three-pronged pelvic structure. Unlike Triadobatrachus, Prosalirus had already lost nearly all of its tail.
The earliest true frog is Vieraella herbsti, from the early Jurassic (188–213 million years ago). It is known only from the dorsal and ventral impressions of a single animal and was estimated to be 33 mm from snout to vent. Notobatrachus degiustoi from the middle Jurassic is slightly younger, about 155–170 million years old. It is likely the evolution of modern Anura was completed by the Jurassic period. The main evolutionary changes involved the shortening of the body and the loss of the tail.
The earliest full fossil record of a modern frog is of sanyanlichan, which lived 125 million years ago and had all modern frog features, but bore 9 presacral vertebrae instead of the 8 of modern frogs, apparently still being a transitional species.
Frog fossils have been found on all continents, including Antarctica.
Uses in agriculture and research
- For more details on this topic, see animal testing on frogs.
Frogs are raised commercially for several purposes. Frogs are used as a food source; frog legs are a delicacy in China, France, the Philippines, the north of Greece and in many parts of the American South, especially Louisiana. Dead frogs are sometimes used for dissections in high school and university anatomy classes, often after being injected with coloured plastics to enhance the contrast between the organs. This practice has declined in recent years with the increasing concerns about animal welfare.
Frogs have served as important model organisms throughout the history of science. Eighteenth-century biologist Luigi Galvani discovered the link between electricity and the nervous system through studying frogs. The African clawed frog or platanna (Xenopus laevis) was first widely used in laboratories in pregnancy assays in the first half of the 20th century. When human chorionic gonadotropin, a hormone found in substantial quantities in the urine of pregnant women, is injected into a female X. laevis, it induces them to lay eggs. In 1952, Robert Briggs and Thomas J. King cloned a frog by somatic cell nuclear transfer, the same technique later used to create Dolly the Sheep, their experiment was the first time successful nuclear transplantation had been accomplished in metazoans.
Frogs are used in cloning research and other branches of embryology because frogs are among the closest living relatives of man to lack egg shells characteristic of most other vertebrates, and therefore facilitate observations of early development. Although alternative pregnancy assays have been developed, biologists continue to use Xenopus as a model organism in developmental biology because it is easy to raise in captivity and has a large and easily manipulatable embryo. Recently, X. laevis is increasingly being displaced by its smaller relative X. tropicalis, which reaches its reproductive age in five months rather than one to two years (as in X. laevis), facilitating faster studies across generations. The genome sequence of X. tropicalis will probably be completed by 2015 at the latest.
- For more details on this topic, see Frogs in popular culture.
Frogs feature prominently in folklore, fairy tales and popular culture. They tend to be portrayed as benign, ugly, clumsy, but with hidden talents. Examples include Michigan J. Frog, The Frog Prince, and Kermit the Frog. Michigan J. Frog, featured in a Warner Brothers cartoon, only performs his singing and dancing routine for his owner. Once another person looks at him, he will return to a frog-like pose. "The Frog Prince" is a fairy tale of a frog who turns into a handsome prince once kissed. Kermit the Frog, on the other hand, is a conscientious and disciplined character of Sesame Street and The Muppet Show; while openly friendly and greatly talented, he is often portrayed as cringing at the fanciful behaviour of more flamboyant characters.
- Indo-European etymology database
- Ford, L.S., D.C. Cannatella (1993). The major clades of frogs. Herpetological Monographs 7: 94–117.
- Faivovich, J., C.F.B. Haddad, P.C.A. Garcia, D.R. Frost, J.A. Campbell, and W.C. Wheeler. Systematic review of the frog family Hylidae, with special reference to Hylinae: Phylogenetic analysis and taxonomic revision. Bulletin of the American Museum of Natural History 294: 1–240.
- Emerson, S.B., Diehl, D. (1980). Toe pad morphology and mechanisms of sticking in frogs. Biol. J. Linn. Soc. 13 (3): 199–216.
- Harvey, M. B, A. J. Pemberton, and E. N. Smith (2002). New and poorly known parachuting frogs (Rhacophoridae : Rhacophorus) from Sumatra and Java. Herpetological Monographs 16: 46–92.
- Saporito, R.A., H.M. Garraffo, M.A. Donnelly, A.L. Edwards, J.T. Longino, and J.W. Daly (2004). Formicine ants: An arthropod source for the pumiliotoxin alkaloids of dendrobatid poison frogs. Proceedings of the National Academy of Science 101: 8045–8050.
- Smith, B. P., Tyler M. J., Kaneko T., Garraffo H. M., Spande T. F., Daly J. W. (2002). Evidence for biosynthesis of pseudophrynamine alkaloids by an Australian myobatrachid frog (pseudophryne) and for sequestration of dietary pumiliotoxins. J Nat Prod 65 (4): 439–47.
- Myers, C.W., J.W. Daly (1983). Dart-poison frogs. Scientific American 248: 120–133.
- Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica, University of Chicago Press, Chicago.
- Duellman, W. E. (1978). The Biology of an Equatorial Herpetofauna in Amazonian Ecuador. University of Kansas Museum of Natural History Miscellaneous Publication 65: 1–352.
- VanCompernolle, Scott. E., R. J. Taylor, K. Oswald-Richter, J. Jiang, B. E. Youree, J. H. Bowie, M. J. Tyler, M. Conlon, D. Wade, C. Aiken, T. S. Dermody, V. N. KewalRamani, L. A. Rollins-Smith and D. Unutmaz (2005). Antimicrobial peptides from amphibian skin potently inhibit Human Immunodeficiency Virus infection and transfer of virus from dendritic cells to T cells. Journal of Virology 79: 11598–11606.
- Phillipe, G., Angenot L. (2005). Recent developments in the field of arrow and dart poisons. J Ethnopharmacol 100(1–2): 85–91.
- Warkentin, K.M. (1995). Adaptive plasticity in hatching age: a response to predation risk trade-offs. Proceedings of the National Academy of Sciences 92: 3507–3510.
- Silva, H. R., Britto-Pereira M. C., & Caramaschi U. (1989). Frugivory and Seed Dispersal by Hyla truncata, a Neotropical Treefrog. Copeia 1989(3): 781–783.
- Curry-Lindahl (1966). . Biegler. see also http://www.pondturtle.com/lfrog.html#Bufo
- Frogs Found in the U.K.. Retrieved 18 July 2007.
- Crump, M.L. (1996). Parental care among the Amphibia. Advances in the Study of Behavior 25: 109–144.
- See, for instance, Ohio's Toads and Frogs by the Ohio Department of Natural Resources. Retrieved 18 July 2007.
- Roy, Debjani (1997). Communication signals and sexual selection in amphibians. Current Science 72: 923–927.
- "Freaky Frogs," at National Geographic Explorer. Retrieved 18 July 2007.
- Evolution Encyclopedia, Volume 3: Geographical Distribution. Retrieved 18 July 2007.
- Stuart, S.N., J.S. Chanson, N.A. Cox, B.E. Young, A.S.L. Rodrigues, D.L. Fischman, and R.W. Waller (2004). Status and trends of amphibian declines and extinctions worldwide. Science 306: 1783–1786.
- Phillips, Kathryn (1994). Tracking the Vanishing Frogs, New York: Penguin Books. ISBN 0-14-024646-0.
- New Scientist (July 7, 2006). Frog population decrease mostly due to traffic. New Scientist.
- Robert W. Briggs Biographical Memoir. URL accessed on 2006-04-22.
- Developing the potential of Xenopus tropicalis as a genetic model. URL accessed on 2006-03-09.
- Joint Genome Institute - Xenopus tropicalis Home. URL accessed on 2006-03-03.
- Berrin, Katherine & Larco Museum. The Spirit of Ancient Peru:Treasures from the Museo Arqueológico Rafael Larco Herrera. New York: Thames and Hudson, 1997.
- Beltz, Ellin (2005). Frogs: Inside their Remarkable World, Firefly Books. ISBN 1552978699.
- Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition, Fog City Press. ISBN 1-877019-69-0.
- Estes, R., and O. A. Reig. (1973). "The early fossil record of frogs: a review of the evidence." pp. 11–63 In J. L. Vial (Ed.), Evolutionary Biology of the Anurans: Contemporary Research on Major Problems. University of Missouri Press, Columbia.
- Gissi, Carmela, Diego San Mauro, Graziano Pesole and Rafael Zardoya (February 2006). Mitochondrial phylogeny of Anura (Amphibia): A case study of congruent phylogenetic reconstruction using amino acid and nucleotide characters. Gene 366: 228–237.
- Holman, J. A (2004). Fossil Frogs and Toads of North America, Indiana University Press. ISBN 0-253-34280-5.
- San Mauro, Diego, Miguel Vences, Marina Alcobendas, Rafael Zardoya and Axel Meyer (May 2005). Initial diversification of living amphibians predated the breakup of Pangaea. American Naturalist 165: 590–599.
- Tyler, M. J. (1994). Australian Frogs A Natural History, Reed Books. ISBN 0-7301-0468-0.
- Amezquita, A., Castellanos, L., & Hodl, W. (2005). Auditory matching of male Epipedobates femoralis (Anura: Dendrobatidae) under field conditions: Animal Behaviour Vol 70(6) Dec 2005, 1377-1386.
- Bee, M. A. (2001). Habituation and sensitization of aggression in bullfrogs (Rana catesbeiana): Testing the dual-process theory of habituation: Journal of Comparative Psychology Vol 115(3) Sep 2001, 307-316.
- Bee, M. A. (2001). Vocally mediated neighbor recognition in north american bullfrogs, rana catesbeiana: Identification, perception, and learning. Dissertation Abstracts International: Section B: The Sciences and Engineering.
- Bee, M. A. (2007). Selective phonotaxis by male wood frogs (Rana sylvatica) to the sound of a chorus: Behavioral Ecology and Sociobiology Vol 61(6) Apr 2007, 955-966.
- Bee, M. A. (2007). Sound source segregation in grey treefrogs: Spatial release from masking by the sound of a chorus: Animal Behaviour Vol 74(3) Sep 2007, 549-558.
- Bee, M. A., & Gerhardt, H. C. (2001). Neighbour-stranger discrimination by territorial male bullfrogs (Rana catesbeiana): I. Acoustic basis: Animal Behaviour Vol 62(6) Dec 2001, 1129-1140.
- Bee, M. A., & Gerhardt, H. C. (2001). Neighbour-stranger discrimination by territorial male bullfrogs (Rana catesbeiana): II. Perceptual basis: Animal Behaviour Vol 62(6) Dec 2001, 1141-1150.
- Bee, M. A., Kozich, C. E., Blackwell, K. J., & Gerhardt, H. C. (2001). Individual variation in advertisement calls of territorial male green frogs, Rana clamitans: Implications for individual discrimination: Ethology Vol 107(1) Jan 2001, 65-84.
- Bernal, X. E., Rand, A. S., & Ryan, M. J. (2006). Acoustic preferences and localization performance of blood-sucking flies (Corethrella Coquillett) to tungara frog calls: Behavioral Ecology Vol 17(5) Sep-Oct 2006, 709-715.
- Bernal, X. E., Rand, A. S., & Ryan, M. J. (2007). Sex differences in response to nonconspecific advertisement calls: Receiver permissiveness in male and female tungara frogs: Animal Behaviour Vol 73(6) Jun 2007, 955-964.
- Bertulis, A. V. (1966). Functional reorganization of the receptor field of frog retina on change of intensity and field of photic stimulus: Biofizika 11(2) 1966, 314-320.
- Bickford, D. P. (2004). Differential parental care behaviors of arboreal and terrestrial microhylid frogs from Papua New Guinea: Behavioral Ecology and Sociobiology Vol 55(4) Feb 2004, 402-409.
- Biersner, R., & Melzack, R. (1966). Approach-avoidance responses to visual stimuli in frogs: Experimental Neurology 15(4) 1966, 418-424.
- Boatright-Horowitz, S. S., Cheney, C. A., & Simmons, A. M. (1999). Atmospheric and underwater propagation of bullfrog vocalizations: Bioacoustics Vol 9(4) 1999, 257-280.
- Brizzi, R., & Corti, C. (2007). Cutaneous antipredatory secretions and pheromones in anurans and urodeles: Marine and Freshwater Behaviour and Physiology Vol 40(3) Sep 2007, 225-231.
- Burke, E. J., & Murphy, C. G. (2007). How female barking treefrogs, Hyla gratiosa, use multiple call characteristics to select a mate: Animal Behaviour Vol 74(5) Nov 2007, 1463-1472.
- Burmeister, S., Konieczka, J., & Wilczynski, W. (1999). Agonistic encounters in a cricket frog (Acris crepitans) chorus: Behavioral outcomes vary with local competition and within the breeding season: Ethology Vol 105(4) Apr 1999, 335-347.
- Burmeister, S. S. (2005). Sex Differences in the Brain: Plasticity and Constraints. Focus on "Androgen-Induced Vocal Transformation in Adult Female African Clawed Frogs": Journal of Neurophysiology Vol 94(1) Jul 2005, 33-34.
- Burmeister, S. S., Mangiamele, L. A., & Lebonville, C. L. (2008). Acoustic modulation of immediate early gene expression in the auditory midbrain of female tungara frogs: Brain Research Vol 1190 Jan 2008, 105-114.
- Bush, S. L., Gerhardt, H. C., & Schul, J. (2002). Pattern recognition and call preferences in treefrogs (Anura: Hylidae): A quantitative analysis using a no-choice paradigm: Animal Behaviour Vol 63(1) Jan 2002, 7-14.
- Byrne, P. G., & Roberts, J. D. (2004). Intrasexual selection and group spawning in quacking frogs (Crinia georgiana): Behavioral Ecology Vol 15(5) Sep 2004, 872-882.
- Castellano, S., & Rosso, A. (2006). Variation in call temporal properties and female preferences in Hyla intermedia: Behaviour Vol 143(4) Apr 2006, 405-424.
- Castellano, S., & Rosso, A. (2007). Female preferences for multiple attributes in the acoustic signals of the Italian treefrog, Hyla intermedia: Behavioral Ecology and Sociobiology Vol 61(8) Jun 2007, 1293-1302.
- Chaput, M. A., Palouzier-Paulignan, B., Delaleu, J. C., & Duchamp-Viret, P. (2004). Taurine Action on Mitral Cell Activity in the Frog Olfactory Bulb In Vivo: Chemical Senses Vol 29(1) Jan 2004, 83-91.
- Chiu, C.-T., & Kam, Y.-C. (2006). Growth of oophagous tadpoles (Chirixalm eiffingeri: Rhacophoridae) after nest displacement: Implications for maternal care and nest homing: Behaviour Vol 143(1) Jan 2006, 123-139.
- Chu, J., Marler, C. A., & Wilczynski, W. (1998). The effects of arginine vasotocin on the calling behavior of male cricket frogs in changing social contexts: Hormones and Behavior Vol 34(3) Dec 1998, 248-261.
- Chu, J., & Wilczynski, W. (2007). Apomorphine effects on frog locomotor behavior: Physiology & Behavior Vol 91(1) May 2007, 71-76.
- Coen, L., Le Blay, K., Rowe, I., & Demeneix, B. A. (2007). Caspase-9 regulates apoptosis/proliferation balance during metamorphic brain remodeling in Xenopus: PNAS Proceedings of the National Academy of Sciences of the United States of America Vol 104(20) May 2007, 8502-8507.
- Darst, C. R., & Cummings, M. E. (2006). Predator learning favours mimicry of a less-toxic model in poison frogs: Nature Vol 440(7081) Mar 2006, 208-211.
- Darst, C. R., Cummings, M. E., Cannatella, D. C., & Wake, D. B. (2006). A mechanism for diversity in warning signals: Conspicuousness versus toxicity in poison frogs: PNAS Proceedings of the National Academy of Sciences of the United States of America Vol 103(15) Apr 2006, 5852-5857.
- d'Avella, A., & Bizzi, E. (2005). Shared and specific muscle synergies in natural motor behaviors: PNAS Proceedings of the National Academy of Sciences of the United States of America Vol 102(8) Feb 2005, 3076-3081.
- Diego-Rasilla, F. J., & Phillips, J. B. (2007). Magnetic compass orientation in Larval Iberian green frogs, Pelophylax perezi: Ethology Vol 113(5) May 2007, 474-479.
- Felton, A., Alford, R. A., Felton, A. M., & Schwarzkopf, L. (2006). Multiple mate choice criteria and the importance of age for male mating success in the microhylid frog, Cophixalus ornatus: Behavioral Ecology and Sociobiology Vol 59(6) Apr 2006, 786-795.
- Ficetola, G. F., & De Bernardi, F. (2005). Interspecific Social Interactions and Breeding Success of the Frog Rana latastei: A Field Study: Ethology Vol 111(8) Aug 2005, 764-774.
- Ficetola, G. F., & De Bernardi, F. (2006). Testing Experimental Results in the Field: Reply to Hettyey and Pearman: Ethology Vol 112(9) Sep 2006, 932-933.
- Finkelstein, D., & Grusser, O.-J. (1965). Frog retina: Detection of movement: Science 150(3699) 1965, 1050-1051.
- Franzisket, L. (1963). Characteristics of instinctive behavior and learning in reflex activity of the frog: Animal Behaviour 11(2 & 3) 1963, 318-324.
- Gesteland, R. C. (1964). Initial events of the electro-olfactogram: Annals of the New York Academy of Sciences 116(2) 1964, 440-447.
- Gonzalo, A., Lopez, P., & Martin, J. (2007). Iberian green frog tadpoles may learn to recognize novel predators from chemical alarm cues of conspecifics: Animal Behaviour Vol 74(3) Sep 2007, 447-453.
- Gribenski, A. (1964). The bidirectional activity of the horizontal semi-circular canals of the frog: Acta Otolaryngologica 58(4) 1964, 355-364.
- Gribenski, A. (1964). Substitution of a vertical semi-circular canal with a horizontal canal in the frog: Acta Otolaryngologica 58(5) 1964, 449-458.
- Haber, V. R. (1926). The food of the Carolina tree frog, Hyla cinerea Schneider: Journal of Comparative Psychology Vol 6(2) Apr 1926, 189-220.
- Hakansson, P., & Loman, J. (2004). Communal Spawning in the Common Frog Rana temporaria - Egg Temperature and Predation Consequences: Ethology Vol 110(9) Sep 2004, 665-680.
- Hargitt, C. W. (1912). Behavior and color changes of tree frogs: Journal of Animal Behavior Vol 2(1) Jan-Feb 1912, 51-78.
- Hart, C. B., & Giszter, S. F. (2004). Modular Premotor Drives and Unit Bursts as Primitives for Frog Motor Behaviors: Journal of Neuroscience Vol 24(22) Jun 2004, 5269-5282.
- Hettyey, A., & Pearman, P. B. (2003). Social environment and reproductive interference affect reproductive success in the frog Rana latastei: Behavioral Ecology Vol 14(2) Mar 2003, 294-300.
- Hettyey, A., & Pearman, P. B. (2006). Testing Experimental Results in the Field: Comment on Ficetola and De Bernardi (2005): Ethology Vol 112(9) Sep 2006, 930-931.
- Hettyey, A., & Roberts, J. D. (2006). Sperm traits of the quacking frog, Crinia georgiana: Intra- and interpopulation variation in a species with a high risk of sperm competition: Behavioral Ecology and Sociobiology Vol 59(3) Jan 2006, 389-396.
- Hettyey, A., & Roberts, J. D. (2007). Sperm traits in the quacking frog (Crinia georgiana), a species with plastic alternative mating tactics: Behavioral Ecology and Sociobiology Vol 61(8) Jun 2007, 1303-1310.
- Hobel, G., & Gerhardt, H. C. (2007). Sources of selection on signal timing in a tree frog: Ethology Vol 113(10) Oct 2007, 973-982.
- Hoke, K. L., Ryan, M. J., & Wilczynski, W. (2005). Social cues shift functional connectivity in the hypothalamus: PNAS Proceedings of the National Academy of Sciences of the United States of America Vol 102(30) Jul 2005, 10712-10717.
- Hoke, K. L., Ryan, M. J., & Wilczynski, W. (2007). Functional coupling between substantia nigra and basal ganglia homologues in amphibians: Behavioral Neuroscience Vol 121(6) Dec 2007, 1393-1399.
- Horowitz, S. S., & Simmons, A. M. (2007). Dynamic visualization of the developing nervous system of the bullfrog, Rana catesbeiana: Brain Research Vol 1157 Jul 2007, 23-31.
- Horowitz, S. S., Tanyu, L. H., & Simmons, A. M. (2007). Multiple mechanosensory modalities influence development of auditory function: Journal of Neuroscience Vol 27(4) Jan 2007, 782-790.
- Humfeld, S. C. (2008). Intersexual dynamics mediate the expression of satellite mating tactics: Unattractive males and parallel preferences: Animal Behaviour Vol 75(1) Jan 2008, 205-215.
- Hutchison, J. B. (1964). Investigations on the neural control of clasping and feeding in Xenopus laevis (Daudin): Behaviour 24(1-2) 1964, 47-66.
- Hutchison, J. B., & Poynton, J. C. (1963). A neurological study of the clasp reflex in Xenopus laevis (Daudin.): Behaviour 22(1-2) 1963, 41-63.
- Huynh, P., & Boyd, S. K. (2007). Nitric oxide synthase and NADPH diaphorase distribution in the bullfrog (rana catesbeiana) CNS: Pathways and functional implications: Brain, Behavior and Evolution Vol 70(3) Sep 2007, 145-163.
- Imendra, K. G., Miyamoto, T., Okada, Y., & Toda, K. (2002). Serotonin differentially modulates the electrical properties of different subsets of taste receptor cells in bullfrog: European Journal of Neuroscience Vol 16(4) Aug 2002, 629-640.
- Ingle, D. (1998). Perceptual constancies in lower vertebrates. New York, NY: Cambridge University Press.
- Ishikane, H., Gangi, M., Honda, S., & Tachibana, M. (2005). Synchronized retinal oscillations encode essential information for escape behavior in frogs: Nature Neuroscience Vol 8(8) Aug 2005, 1087-1095.
- Ishikane, H., Gangi, M., & Tachibana, M. (2002). Synchronous oscillations in frog retinal ganglion cells: Japanese Journal of Psychonomic Science Vol 21(1) Sep 2002, 47-48.
- Ivanov, V. A. (1965). On the mechanism of lateral inhibition in frog retina: Biofizika 10(5) 1965, 903-905.
- Jelaso, A. M., & DeLong, C. (2005). NGF and IL-1beta are co-localized in the developing nervous system of the frog, Xenopus laevis: International Journal of Developmental Neuroscience Vol 23(7) Nov 2005, 575-586.
- Kamenskii, Y. I. (1964). The effect of microwaves on the functional state of the nerve: Biofizika 9(6) 1964, 695-700.
- Kelley, D. B. (2004). Vocal communication in frogs: Current Opinion in Neurobiology Vol 14(6) Dec 2004, 751-757.
- Kime, N. M., Burmeister, S. S., & Ryan, M. J. (2004). Female preferences for socially variable call characters in the cricket frog, Acris crepitans: Animal Behaviour Vol 68(6) Dec 2004, 1391-1399.
- Kime, N. M., Whitney, T. K., Davis, E. S., & Marler, C. A. (2007). Arginine vasotocin promotes calling behavior and call changes in male tungara frogs: Brain, Behavior and Evolution Vol 69(4) Apr 2007, 254-265.
- Kirkpatrick, M., Rand, A. S., & Ryan, M. J. (2006). Mate choice rules in animals: Animal Behaviour Vol 71(5) May 2006, 1215-1225.
- Kiziltan, E., & Pehlivan, F. (2006). Assesment criteria for experimental demyelination induced in frog peripheral nerve: International Journal of Neuroscience Vol 116(12) Dec 2006, 1431-1446.
- Klomberg, K. F., & Marler, C. A. (2000). The neuropeptide arginine vasotocin alters male call characteristics involved in social interactions in the grey treefrog, Hyla versicolor: Animal Behaviour Vol 59(4) Apr 2000, 807-812.
- Kuffler, D. P., Lyfenko, A., Vyklicky, L., & Vlachova, V. (2002). Cellular Mechanisms of Nociception in the Frog: Journal of Neurophysiology Vol 88(4) Oct 2002, 1843-1850.
- Lamb, M. J. (2007). Modeling behavior-based depth vision in frog and salamander. Dissertation Abstracts International: Section B: The Sciences and Engineering.
- Lardner, B., & Lakim, M. B. (2004). Female call preferences in tree-hole frogs: Why are there so many unattractive males? : Animal Behaviour Vol 68(2) Aug 2004, 265-272.
- Lengagne, T., Grolet, O., & Joly, P. (2006). Male mating speed promote hybridization in the Rana lessonae--Rana esculente waterfrog system: Behavioral Ecology and Sociobiology Vol 60(2) Jun 2006, 123-130.
- Li, W. C., Higashijima, S.-i., Parry, D. M., Roberts, A., & Soffe, S. R. (2004). Primitive Roles for Inhibitory Interneurons in Developing Frog Spinal Cord: Journal of Neuroscience Vol 24(25) Jun 2004, 5840-5848.
- Lynch, K. S., Rand, A. S., Ryan, M. J., & Wilczynski, W. (2005). Plasticity in female mate choice associated with changing reproductive states: Animal Behaviour Vol 69(3) Mar 2005, 689-699.
- Maksimov, V. V., Zenkin, G. M., & Byzov, A. L. (1965). Study of the functional properties of bipolars of two types in the retina of the frog: Biofizika 10(1) 1965, 141-147.
- Mann, K. M., & Sleigh, M. J. (2003). Effects of perinatal visual stimulation on preference, growth, and mortality in African clawed frogs ( Xenopus laevis): Developmental Psychobiology Vol 43(1) Jul 2003, 28-36.
- Marquez, R., Bosch, J., & Penna, M. (2006). Sound Pressure Level of Advertisement Calls of Alytes cisternasii and Alytes obstetricans (Anura, Discoglossidae): Bioacoustics Vol 16(1) 2006, 27-37.
- Marshall, V. T., Humfeld, S. C., & Bee, M. A. (2003). Plasticity of aggressive signalling and its evolution in male spring peepers, Pseudacris crucifer: Animal Behaviour Vol 65(6) Jun 2003, 1223-1234.
- Marshall, V. T., Schwartz, J. J., & Gerhardt, H. C. (2006). Effects of heterospecific call overlap on the phonotactic behaviour of grey treefrogs: Animal Behaviour Vol 72(2) Aug 2006, 449-459.
- Martin, J., Luque-Larena, J. J., & Lopez, P. (2006). Collective detection in escape responses of temporary groups of Iberian green frogs: Behavioral Ecology Vol 17(2) Mar-Apr 2006, 221-226.
- Mason, M. J., Lin, C. C., & Narins, P. M. (2003). Sex differences in the middle ear of the bullfrog (Rana catesbeiana): Brain, Behavior and Evolution Vol 61(2) Mar 2003, 91-101.
- McGill, T. E. (1960). Response of the leopard frog to electric shock in an escape-learning situation: Journal of Comparative and Physiological Psychology Vol 53(5) Oct 1960, 443-445.
- Moreno, N., Morona, R., Lopez, J. M., Munoz, M., & Gonzalez, A. (2005). Lateral and medial amygdala of anuran amphibians and their relation to olfactory and vomeronasal information: Brain Research Bulletin Vol 66(4-6) Sep 2005, 332-336.
- Mozell, M. M. (1964). Olfactory discrimination: Electrophysiological spatiotemporal basis: Science 143(Whole No 3612) 1964, 1336-1337.
- Munn, N. L. (1940). Learning experiments with larval frogs. A preliminary report: Journal of Comparative Psychology Vol 29(1) Feb 1940, 97-108.
- Muntz, W. R. A. (1964). Vision in frogs: Scientific American 210(3) 1964, 111-119.
- Murphy, C. G., & Floyd, S. B. (2005). The effect of call amplitude on male spacing in choruses of barking treefrogs, Hyla gratiosa: Animal Behaviour Vol 69(2) Feb 2005, 419-426.
- Murphy, C. G., & Gerhardt, H. C. (2002). Mate sampling by female barking treefrogs (Hyla gratiosa): Behavioral Ecology Vol 13(4) Aug 2002, 472-480.
- Murphy, P. J. (1999). The interplay between uncertain juvenile recruitment and reproductive strategy in the neotropical frog edalorhina perezi. (risk assessment). Dissertation Abstracts International: Section B: The Sciences and Engineering.
- Murphy, P. J. (2003). Context-dependent reproductive site choice in a Neotropical frog: Behavioral Ecology Vol 14(5) Sep-Oct 2003, 626-633.
- Nistri, M., & Deluca, P. L. (1964). Inhibition of ejaculation during treatment with thioridazine: Its eventual therapeutic value: L'Encephale 53(1) 1964, 203-206.
- No authorship, i. (1906). Review of Bahnung und Hemmung der Reactionen auf tactile Reize durch akustische Reize beim Frosche: Psychological Bulletin Vol 3(5) May 1906, 166-167.
- No authorship, i. (1906). Review of The Sense of Hearing in Frogs: Psychological Bulletin Vol 3(5) May 1906, 165.
- Oristaglio, J. T. (2005). Variability in frog prey orienting behavior: New insights into visuomotor processing (Rana pipiens). Dissertation Abstracts International: Section B: The Sciences and Engineering.
- Owen, P. C., & Gordon, N. M. (2005). The effect of perceived intruder proximity and resident body size on the aggressive responses of male green frogs, Rana clamitans (Anura: Ranidae): Behavioral Ecology and Sociobiology Vol 58(5) Sep 2005, 446-455.
- Pearl, C. A., Cervantes, M., Chan, M., Ho, U., Shoji, R., & Thomas, E. O. (2000). Evidence for a mate-attracting chemosignal in the dwarf African clawed frog Hymenochirus: Hormones and Behavior Vol 38(1) Aug 2000, 67-74.
- Penna, M., & Hamilton-West, C. (2007). Susceptibility of evoked vocal responses to noise exposure in a frog of the temperate austral forest: Animal Behaviour Vol 74(1) Jul 2007, 45-56.
- Penna, M., Pottstock, H., & Velasquez, N. (2005). Effect of natural and synthetic noise on evoked vocal responses in a frog of the temperate austral forest: Animal Behaviour Vol 70(3) Sep 2005, 639-651.
- Phelps, S. M., Rand, A. S., & Ryan, M. J. (2007). The mixed-species chorus as public information: Tungara frogs eavesdrop on a heterospecific: Behavioral Ecology Vol 18(1) Jan-Feb 2007, 108-114.
- Prohl, H. (2003). Variation in male calling behaviour and relation to male mating success in the strawberry poison frog (Dendrobates pumilio): Ethology Vol 109(4) Apr 2003, 273-290.
- Prohl, H. (2005). Clutch loss affects the operational sex ratio in the strawberry poison frog Dendrobates pumilio: Behavioral Ecology and Sociobiology Vol 58(3) Jul 2005, 310-315.
- Prohl, H., Hagemann, S., Karsch, J., & Hobel, G. (2007). Geographic variation in male sexual signals in strawberry poison frogs (Dendrobates pumilio): Ethology Vol 113(9) Sep 2007, 825-837.
- Racz, E., Bacskai, T., Szabo, G., Szekely, G., & Matesz, C. (2008). Organization of last-order premotor interneurons related to the protraction of tongue in the frog, Rana esculenta: Brain Research Vol 1187 Jan 2008, 111-115.
- Rapuzzi, G., & Casella, C. (1965). Innervation of the fungiform papillae in the frog tongue: Journal of Neurophysiology 28(1) 1965, 154-165.
- Reyer, H.-U., Niederer, B., & Hettyey, A. (2003). Variation in fertilisation abilities between hemiclonal hybrid and sexual parental males of sympatric water frogs ( Rana lessonae, R. esculenta, R. ridibunda ): Behavioral Ecology and Sociobiology Vol 54(3) Aug 2003, 274-284.
- Rhodes, H. J., Yu, H. J., & Yamaguchi, A. (2007). Xenopus vocalizations are controlled by a sexually differentiated hindbrain central pattern generator: Journal of Neuroscience Vol 27(6) Feb 2007, 1485-1497.
- Robins, A., & Rogers, L. J. (2006). Lateralized visual and motor responses in the green tree frog, Litoria caerulea: Animal Behaviour Vol 72(4) Oct 2006, 843-852.
- Rojas, B., Amezquita, A., & Delgadillo, A. (2006). Matching and Symmetry in the Frequency Recognition Curve of the Poison Frog Epipedobates trivittatus: Ethology Vol 112(6) Jun 2006, 564-571.
- Rosso, A., Castellano, S., & Giacoma, C. (2006). Preferences for Call Spectral Properties in Hyla intermedia: Ethology Vol 112(6) Jun 2006, 599-607.
- Rutherford, M. A., & Roberts, W. M. (2006). Frequency selectivity of synaptic exocytosis in frog saccular hair cells: PNAS Proceedings of the National Academy of Sciences of the United States of America Vol 103(8) Feb 2006, 2898-2903.
- Saltzman, H., Zacharatos, M., & Gruberg, E. R. (2004). Recognition of Apertures in Overhead Transparent Barriers by Leopard Frogs: Brain, Behavior and Evolution Vol 64(1) Jun 2004, 11-18.
- Sato, T., Okada, Y., Miyazaki, T., Kato, Y., & Toda, K. (2005). Taste Cell Responses in the Frog Are Modulated by Parasympathetic Efferent Nerve Fibers: Chemical Senses Vol 30(9) Nov 2005, 761-769.
- Sato, T., Okada, Y., & Toda, K. (2004). Analysis of Slow Hyperpolarizing Potentials in Frog Taste Cells Induced by Glossopharyngeal Nerve Stimulation: Chemical Senses Vol 29(8) Oct 2004, 651-657.
- Schaeffer, A. A. (1911). Habit formation in frogs: Journal of Animal Behavior Vol 1(5) Sep-Oct 1911, 309-335.
- Schmidt, R. S. (1964). Hearing and responses to calls in anurans: Behaviour 23(3-4) 1964, 280-293.
- Schmidt, R. S. (1966). Central mechanisms of frog calling: Behaviour 26(3-4) 1966, 251-285.
- Schwartz, J. J., Huth, K., & Hutchin, T. (2004). How long do females really listen? Assessment time for female mate choice in the grey treefrog, Hyla versicolor: Animal Behaviour Vol 68(3) Sep 2004, 533-540.
- Scroggie, M. P., & Littlejohn, M. J. (2005). Territorial vocal behavior in hybrid smooth froglets, Geocrinia laevis complex (Anura: Myobatrachidae): Behavioral Ecology and Sociobiology Vol 58(1) May 2005, 72-79.
- Shear, L., Bell, P., & Linn, M. C. (2004). Partnership models: The case of the deformed frogs. Mahwah, NJ: Lawrence Erlbaum Associates Publishers.
- Sidis, B. (1908). An experimental study of sleep: The Journal of Abnormal Psychology Vol 3(1) Apr-May 1908, 1-32.
- Sidis, B. (1908). An experimental study of sleep. Chapters I, II, III, IV, V, VI, and VII: The Journal of Abnormal Psychology Vol 3(1) Apr-May 1908, 1-32.
- Simmons, A. M., & Bean, M. E. (2000). Perception of mistuned harmonics in complex sounds by the bullfrog (Rana catesbeiana): Journal of Comparative Psychology Vol 114(2) Jun 2000, 167-173.
- Smith, M. J., & Hunter, D. (2005). Temporal and geographic variation in the advertisement call of the Booroolong frog (Litoria booroolongensis: Anura: Hylidae): Ethology Vol 111(12) Dec 2005, 1103-1115.
- Smith, M. J., & Roberts, J. D. (2003). Call structure may affect male mating success in the quacking frog Crinia georgiana (Anura: Myobatrachidae): Behavioral Ecology and Sociobiology Vol 53(4) Mar 2003, 221-226.
- Smith, M. J., & Roberts, J. D. (2003). An experimental examination of female preference patterns for components of the male advertisement call in the quacking frog, Crinia georgiana: Behavioral Ecology and Sociobiology Vol 55(2) Dec 2003, 144-150.
- Spigel, I. M., & Ellis, K. R. (1965). Brightness preference in the frog: Perceptual and Motor Skills 21(2) 1965, 367-370.
- Steiner, U. K. (2007). Linking antipredator behaviour, ingestion, gut evacuation and costs of predator-induced responses in tadpoles: Animal Behaviour Vol 74(5) Nov 2007, 1473-1479.
- Stull, A. K., & Gruberg, E. R. (1998). Prey selection in the leopard frog: Choosing in biased and unbiased situations: Brain, Behavior and Evolution Vol 52(1) Jul 1998, 37-45.
- Tarano, Z., & Herrera, E. A. (2003). Female Preferences for Call Traits and Male Mating Success in the Neotropical Frog Physalaemus enesefae: Ethology Vol 109(2) Feb 2003, 121-134.
- Tarano, Z., & Ryan, M. J. (2002). No pre-existing biases for heterospecfic call for traits in the frog: Physalaemus enesefae: Animal Behaviour Vol 64(4) Oct 2002, 599-607.
- Taylor, F. V. (1936). The effect of transposition of the Achilles tendon on the walking and righting movements of the frog: Journal of Comparative Psychology Vol 21(2) Apr 1936, 245-273.
- Templin, T. (2008). Histomorphological and histochemical development of the superior olive and the lateral lemniscus in Rana catesbeiana across metamorphosis. Dissertation Abstracts International: Section B: The Sciences and Engineering.
- Tobias, M. L., Barnard, C., O'Hagan, R., Horng, S. H., Rand, M., & Kelley, D. B. (2004). Vocal communication between male Xenopus laevis: Animal Behaviour Vol 67(2) Feb 2004, 353-365.
- Tomaru, A., & Kurahashi, T. (2005). Mechanisms Determining the Dynamic Range of the Bullfrog Olfactory Receptor Cell: Journal of Neurophysiology Vol 93(4) Apr 2005, 1880-1888.
- Trainor, B. C., Rouse, K. L., & Marler, C. A. (2003). Arginine vasotocin interacts with the social environment to regulate advertisement calling in the gray treefrog (Hyla versicolor): Brain, Behavior and Evolution Vol 61(4) Jun 2003, 165-171.
- Van Buskirk, J., Muller, C., Portmann, A., & Surbeck, M. (2002). A test of the risk allocation hypothesis: Tadpole responses to temporal change in predation risk: Behavioral Ecology Vol 13(4) Aug 2002, 526-530.
- van Dijk, P., Narins, P. M., & Mason, M. J. (2003). Physiological vulnerability of distortion product otoacoustic emissions from the amphibian ear: Journal of the Acoustical Society of America Vol 114(4,Pt1) Oct 2003, 2044-2048.
- Voronin, G. V., Tott, S., & Sokolov, E. N. (1964). Amplitude-phase frequency analysis of retinal biopotentials during sinusoidal photic stimulation: Biofizika 9(1) 1964, 94-103.
- Wabnitz, P. A., Bowie, J. H., Tyler, M. J., Wallace, J. C., & Smith, B. P. (1999). Aquatic sex pheromone from a male tree frog: Nature Vol 401(6752) Sep 1999, 444-445.
- Waldman, B., & Bishop, P. J. (2004). Chemical communication in an archaic anuran amphibian: Behavioral Ecology Vol 15(1) Jan 2004, 88-93.
- Weiss, B. A., & Strother, W. F. (1965). Hearing in the green treefrog (Hyla cinerea cinerea): Journal of Auditory Research 5(4) 1965, 297-306.
- Wente, W. H., & Phillips, J. B. (2005). Microhabitat selection by the Pacific treefrog, Hyla regilla: Animal Behaviour Vol 70(2) Aug 2005, 279-287.
- Wickramasinghe, D. D., Oseen, K. L., Kotagama, S. W., & Wassersug, R. J. (2004). The terrestrial breeding biology of the ranid rock frog Nannophrys ceylonensis: Behaviour Vol 141(7) Jul 2004, 899-913.
- Wollerman, L., & Wiley, R. H. (2002). Background noise from a natural chorus alters female discrimination of male calls in a neotropical frog: Animal Behaviour Vol 63(1) Jan 2002, 15-22.
- Wollerman, L., & Wiley, R. H. (2002). Erratum: Background noise from a natural chorus alters female discrimination of male calls in a neotropical frog, Animal Behaviour, 63, 15-22: Animal Behaviour Vol 63(5) May 2002, 1027.
- Yamaguchi, A., & Kelley, D. B. (2000). Generating sexually differentiated vocal patterns: Laryngeal nerve and EMG recordings from vocalizing male and female African clawed frogs (Xenopus laevis): Journal of Neuroscience Vol 20(4) Feb 2000, 1559-1567.
- Yao, M., Westphal, N. J., & Denver, R. J. (2004). Distribution and Acute Stressor-Induced Activation of Corticotrophin-Releasing Hormone Neurones in the Central Nervous System of Xenopus Iaevis: Journal of Neuroendocrinology Vol 16(11) Nov 2004, 880-893.
- Zenkin, G. M., & Maksimov, V. V. (1964). An investigation of horizontal interaction on the level of slow bipolars of frog retina: Biofizika 9(6) 1964, 718-725.
- Zenkin, G. M., Maksimov, V. V., & Byzov, A. L. (1964). An investigation of horizontal interaction at the level of the slow bipolars in the retina of the frog: Biofizika 9(5) 1964, 612-620.
- The Whole Frog Project - Virtual frog dissection and anatomy
- Xenbase - A Xenopus laevis and tropicalis Web Resource
- Amphibia Web
- Time-lapse video showing the egg's development until hatching
- Frog calls - short video clips of calling frogs and interviews with scientists about frog issues, including declining and malformed frog causes
- Frog calls - Canada
- eastern United States Frog calls - eastern United States
- Frogwatch USA volunteer frog and toad monitoring program by National Wildlife Federation and USGS, includes links to frog calls of the United States
- Amphibian photo gallery by scientific name - features many unusual frogs
- Scientific American: Researchers Pinpoint Source of Poison Frogs' Deadly Defenses
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