Poison dart frog

Poison dart frogs (also dart-poison frogs, dart frogs, poison frogs or formerly poison-arrow frogs) are frogs in the family Dendrobatidae. They are native to tropical rainforests in South America. Unlike most frogs, these species are active during the day and often exhibit brightly-colored bodies. Many, if not most species, secrete a mix of alkaloid neurotoxins through their skins. Some species are considered to be the planet's most toxic animals. Although all wild dendrobatids are at least somewhat toxic, levels of toxicity vary considerably from one species to the next and from one population to another. Many species are critically endangered. These amphibians are often called "dart frogs" due to indigenous Amerindians' use of their toxic secretions to poison the tips of blowdarts.

Classification
Poison dart frogs are members of the suborder Neobatrachia. Like most members of this group, they typically possess no ribs, seven vertebrae and teeth in the upper jaw. Within Neobatrachia, poison dart frogs form their own superfamily, Dendrobatoidea.

The family Dendrobatidae is divided into three subfamilies (Colostethinae, Dendrobatinae, and Hyloxalinae), and twelve genera. Until recently, nearly all of the brightly coloured species were placed in the genera Dendrobates and Epipedobates by default; these two genera were split into several separate genera. Similarly, the genus Colostethus once contained all cryptically coloured species in the family, but lost many of them to Hyloxalus, Silverstoneia, and to the Aromobatidae family.

Taxonomy
Currently, the family Dendrobatidae is classified as follows.


 * Subfamily Colostethinae
 * Genus Ameerega
 * Genus Colostethus
 * Genus Epipedobates
 * Genus Silverstoneia
 * Subfamily Dendrobatinae
 * Genus Adelphobates
 * Genus Andinobates
 * Genus Dendrobates
 * Genus Excidobates
 * Genus Minyobates
 * Genus Oophaga
 * Genus Phyllobates
 * Genus Ranitomeya
 * Subfamily Hyloxalinae
 * Genus Hyloxalus

Toxins and Secretions
Most poison dart frogs secrete lipophilic alkaloid toxins through their skin. Alkaloids in the skin glands of poison frogs serve as a chemical defence against predation, and they are therefore able to be active alongside potential predators during the day. The most toxic of poison-dart frog species is Phyllobates terribilis. About 28 structural classes of alkaloids are known in poison frogs. The most common compounds among the family are the relatively weak pumiliotoxins; several species in the Oophaga, Epipedobates, and Ameerega genera possess the considerably stronger allopumiliotoxins, while five of the six Phyllobates species possess batrachotoxins, the most potent non-peptidal neurotoxins known. It is argued that dart frogs do not synthesize their poisons, but sequester the chemicals from arthropod prey items, such as ants, centipedes and mites. This is known as the dietary hypothesis. Because of this, captive-bred animals do not contain significant levels of toxins. These poisons are mainly neurotoxic, but poison frogs are also known to secrete cardiotoxins, cytotoxins, and others.

Some of the frogs' secretions may have medicinal use. The small phantasmal poison dart frog secretes an alkaloid known as epibatidine, which is a painkiller approximately 200 times more powerful than morphine. Unfortunately there are gastrointestinal side effects, but the structure of epibatidine may lead researchers to other, potent painkillers. Pumiliotoxins, meanwhile, may prove useful as heart stimulants, and even the extremely lethal batrachotoxins, or derivative compounds, may be used to treat severe tachycardia.

Description
Most species of poison dart frogs are small, sometimes less than 1.5 centimetres (0.59 in) in adult length, although a few are up to 6 centimetres (2.4 in) in length. They weigh about 2 grams, depending on the size of the frog. Most poison dart frogs are brightly colored, displaying aposematic patterns to warn potential predators. Their bright coloration is associated with their toxicity and levels of alkaloids. Frogs like the ones of Phyllobates species have high levels of alkaloids, whereas the Hyloxalus species are cryptically colored and are non-toxic. Unlike most other frogs, they are diurnal, rather than being primarily nocturnal or crepuscular. When born and raised in captivity, poison frogs do not produce the skin toxins which they retain in their native habitat.

They lay their eggs in moist places, including on leaves, in plants, among exposed roots, and elsewhere, and allow the tadpoles to wriggle onto their backs shortly after they hatch. They then carry the piggy-backed tadpoles to water, where the larva remain until metamorphosis. The water is typically a pool, but some species use the water gathered in bromeliads or other plants; and some species provide food, supplying the tadpoles with unfertilized eggs to eat.

Habitat and Ecology
Poison dart frogs are distributed from Honduras (with reports of individuals in Guatemala and El Salvador) through Nicaragua, Costa Rica, and Panama, into Colombia, Ecuador, Peru, Bolivia, Brazil, Venezuela, Guyana, Suriname, and French Guyana. They are synonymous with the most humid of tropical rainforests. Some species live on the forest floor, while others have taken to the dense plant cover of the undergrowth and up into the trees. Generally speaking, terrestrial species tend to be larger than arboreal ones; however, a few large species, Phyllobates vittatus among them, do climb regularly.

Dendrobatids are fully carnivorous. All species live on a diet of small insects and other invertebrates, including ants, centipedes, mites, springtails, and beetles. These invertebrates appear to be the source of the frogs' toxicity. As a result of their potent defenses, poison dart frogs have few predators. Mildly toxic species are occasionally hunted by large spiders and scorpions; highly toxic species are almost immune to predation, although a species of snake, Liophis epinephelus, has a limited resistance to batrachotoxins and may occasionally hunt dendrobatid frogs.

Behaviour and Reproduction
Poison dart frogs are typically diurnal (day-active). They forage for food primarily in the morning, and frequently bask in small patches of sunshine, retreating into the leaf litter if they overheat. Some species, such as Oophaga pumilio are quite territorial. Mature male O. pumilio establish tiny "territories" for themselves and defend them against rivals. An intrusion will trigger a confrontation involving calling and posturing, and, from time to time, wrestling. Females and juveniles, meanwhile, are more sociable. Dendrobates  tinctorius is also fiercely territorial, and both males and females will fight to secure territories. Other species, most notably the members of the genus Phyllobates, are sociable and generally non-aggressive. P. terribilis and P. bicolor seem to live in groups throughout the year, while other sociable species become more territorial during the breeding season.

Dendrobatid frogs typically breed during the rainy season. Males will often find perches from which to call to females and to view their surroundings. Unlike many other frogs, poison dart frogs do not call competively and as a result do not form loud choruses. Both male and female poison dart frogs can be formidably aggressive to members of the same sex during times of breeding. Males will attack other males and drive them away to eliminate competition for females. Females will grapple with one another, as, given the opportunity, a female will destroy another's eggs to remove competition for their offspring. Most species are polygamous; Ranitomeya imitator is the exception, with each individual only taking one partner every breeding season.

Poison dart frogs are unusual among other anurans in that they demonstrate parental care. Females of most species lay fairly small clutches of eggs; often around 6 to 20 (though Ameerega species may lay several dozen). The eggs are then attentively guarded by either the male or female, and, in many species, both parents. In addition to providing protection, many male dendrobatids will keep their eggs moist with their own urine. When the eggs hatch, the newborn tadpoles are transported to a source of water by either or both parents. Dendrobatid tadpoles may be fiercely cannibalistic, but some are communal. Dendrobatids with cannibalistic tadpoles will transport their offspring individually. The tadpoles secrete a water-soluble adhesive and stick to the backs of their parents. The adults then carry the tadpoles to small bodies of water, such as the water within plants such as bromeliads. Dendrobatids with communal tadpoles, meanwhile, transport all of their offspring at once; the tadpoles form a cluster around the waste of the adult. Many poison dart frogs guard their tadpoles within their tiny nurseries, and those in the Oophaga and Ranitomeya genera will also supplement the tadpoles' diets by laying unfertilized eggs.

Conservation
Like many frog families, dendrobatids have also been affected by the worldwide decline in amphibian populations. Habitat loss (due to logging and farming) and predation by introduced species are among the more common causes, but the cutaneous chytridiomycosis has struck dart frogs the hardest in the past 25 years. Zoos have tried to counteract this disease by treating captive frogs with an antifungal agent that is used to kill athlete's foot in humans.

In captivity
Poison dart frogs have been kept in captivity since the middle-to-late 20th century. The oldest properly recorded dendrobatid frogs in captivity were Dendrobates tinctorius in the early 1970s. By 1977, poison dart frogs were being succesfully bred in captivity, as the Stuttgart Zoo was reportedly breeding Phyllobates bicolor and Zoo Basel was breeding Dendrobates auratus.

The first documented successful captive propagation of dendrobatids in the United States is a report by David Grow that describes breeding success for Dendrobates auratus at the Sedgwick County Zoo in Wichita, Kansas. By the 1980s, dart-frogs were being kept by hobbyists and not just by zoos and scientific institutions.

All species of poison dart frogs are neotropical in origin. Wild-caught specimens can maintain toxicity for some time, so appropriate care should be taken when handling such animals. While scientific study on the lifespan of poison dart frogs is scant, retagging frequencies indicate it can range from one to three years in the wild. However, these frogs typically live for much longer than that in captivity, having been reported to live as long as 25 years. These claims also seem to be questionable, since many of the larger species take a year or more to mature, and Phyllobates species can take more than two years. In captivity, most species thrive where the humidity is kept constant at 80 to 100% and where the temperature is around 72 °F (22 °C) to 80 °F (27 °C) during the day and no lower than 60 °F (16 °C) to 65 °F (18 °C) at night. Some species tolerate lower temperatures better than others.