poison frog

▪ amphibian

also called  poison dart frog  or  poison arrow frog 

 any of approximately 180 species of New World frogs (frog) characterized by the ability to produce extremely poisonous skin secretions (secretion). Poison frogs inhabit the forests of the New World tropics from Nicaragua to Peru and Brazil, and a few species are used by South American tribes to coat the tips of darts and arrows. Poison frogs, or dendrobatids, are small and range from 12 to 19 mm (0.5 to 0.75 inch) from snout to vent in the minute poison frogs (Minyobates) to about 65 mm (2.6 inches) in the skunk frog (Aromobates nocturnus).

      All frogs (order Anura) produce poisonous skin secretions; however, humans do not notice the toxicity or suffer skin irritation when handling most species. Nonetheless, handling one of the brightly coloured dendrobatids, such as Dendrobates and Phyllobates, requires caution because their alkaloid skin secretions are potentially lethal if absorbed through human mucous membranes (mucous membrane) or passed into the body through a cut on the skin. In fact, the skin secretion of the true poison dart frog, or golden poison frog (Phyllobates terribilis), is so toxic that the tip of a dart rubbed across its back picks up sufficient poison to kill a large bird or a monkey. The origin and production of the toxic skin secretions remains uncertain, but at least in some dendrobatids it appears to be derived from their consumption of beetles (beetle), their primary prey. When kept in captivity and fed a diet devoid of beetles, the skin secretions of poison frogs lack the highly toxic alkaloids.

 Aposematic (conspicuous) or warning coloration is common among distasteful and poisonous species of many plants and animals. The coloration of poison frogs commonly include reds, oranges, yellows, and even bright blues and greens on a black or dark background. Not all dendrobatids are so poisonous or brightly coloured; many are patterned with shades of brown and well camouflaged (as in Colostethus), and their skin secretions are generally nontoxic and nonirritating.

      Parental care of the young, which is often performed by the male, occurs in all poison frog species. The male attracts a female to his residence beneath a leaf or log, and she lays the eggs (egg) and often departs. The male remains to guard the clutch; however, in some species the female remains. When the tadpoles (tadpole) hatch, the parent allows the tadpoles to swim or crawl up onto his or her back. They are subsequently carried to a nearby body of water (such as a stream, a pond, or a tree-hole). There, the tadpoles slide off the back of the parent and into the water to complete their development.

      Superficially, the mantelline frogs of Madagascar (family Mantellidae) appear nearly identical to the dendrobatids; however, they are not closely related. The similarities between the two groups are attributed to convergent evolution (evolution). Also, both are comparable in terms of physical size, as mantellines range from 15 to 120 mm (0.6 inch to nearly 5 inches) from snout to vent, although most species are less than 60 mm (about 2.5 inches) long. While the skin secretions of the mantellines have not been thoroughly studied, the secretions of Mantella are toxic and capable of killing vertebrate predators.

      Mantellines include more than 100 species in three genera of terrestrial to arboreal (tree-dwelling) forms that live in semiarid scrubland to rainforest habitats. Some species lay eggs on leaves that overhang bodies of water, and hatching larvae then drop into the water. Other species lay terrestrial eggs that develop either directly into froglets or into a nonaquatic, nonfeeding tadpole stage. In addition, parental care occurs in some mantelline species with terrestrial eggs.

George R. Zug

 

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