By: David and Ryan, students at Erskine College
Dedicated to Dr. M L Edwards, our teacher and inspiration
Often described as "jewels of the rainforests," dendrobatid frogs, more commonly known as poison dart frogs, are adorned in various vivid colors to warn potential predators of their deadly toxins. This warning coloration is called aposematic coloration. Dendrobatid frogs belong to the Family Dendrobatidae, which is divided into 9 known genera, but only 6 are commonly accepted. Currently there are approximately 165 species of Dendrobatid frogs. The most common genera are Genus Dendrobates and Genus Phyllobates. They have bright patterns of green, red, orange, yellow, blue, white, and/or jet black depending on the species. Scientists have found that Phyllobates have bony plates in their upper jaw, which are sometimes referred to as "teeth" and include the most deadly of the dendrobatid frog species. These frogs have only one known predator, the snake Leimadophis epinephelus, which is immune to the toxins in the frogs.
The dendrobatid frogs live near rivers, streams, and various small bodies of water, while hunting and living in the foliage and leaf litter of the evergreen forest floor. A few species have adapted to life in the trees, and other species can be found in the water, too. Dendrobatid frogs, unlike most frogs, are primarily diurnal and can be seen on the forest floor in broad daylight. Adult frogs receive their nutrition by capturing ants, termites, small insects, and arthropods. The average lifespan of a dendrobatid frog is about 5-7 years, although many live longer than that.
The mating season, occurring after the rainy season has begun, is signaled to begin when sounds of buzzing, humming, chirping, or trilling can be heard all over the forest. Males attract females through elaborate calls, often after careful planning of the best place to store their eggs until the tadpoles are ready to be placed in water. After finding the male, the female deposits a few large eggs on a leaf that is in close proximity of a body of water, the site that the male has carefully decided on. Being near water insures that the eggs will remain moist, which is essential to the tadpoles' growth and development. The leaf usually hangs about 1.2 meters above the forest floor. The male then fertilizes the eggs and is responsible for guarding the eggs and making sure that they stay wet. After 2-4 weeks the tadpoles are ready to be transported to water where they will develop into adult frogs. Many times the male frog carries the tadpoles on his back, which contains a sticky mucus, to a small accumulation of water. In some species the female is responsible for transporation, and in a few species both the male and female seek out the best sites for their baby tadpoles to develop. Many times the parent frogs take each tadpole to a separate place because the tadpoles are cannbalistic. How they remember the multiple locations is still unknown. Good sites for developing tadpoles tend to be bromeliad funnels, branches, hollow trees, and bamboo stalks. One species even uses the rain filled "monkey pots" found on the forest floor that are produced by Brazil nut trees. The frogs feed the tadpoles unfertilized eggs about once every five days and show parental care. After about 2-3 months, the tadpoles have completely developed into adult frogs and are ready to pass on their genes to yet another generation of dendrobatid frogs.
Although usually found on the forest floor, dendrobates do have glandular muscular adhesive bands on their toes which are almost exactly like the tree frogs. The dendrobatid frogs secrete alkaloid poisons, which are complex and bitter-tasting. Alkaloid poisons, which include caffine, nicotine, cannabidiol, cocaine, and morphine, are some of the most familiar and addictive drugs known to man. They tend to interfere with liver and cell membrane function, and they can cause cessation of lactation, birth defects, or abortion. Alkaloid chemicals are harmful to numerous animals, and three species have been found that can be harmful and even deadly to humans: Phyllobates terribilis, Phyllobates aurotaenia, and Phyllobates bicolor. Phyllobates terribilis is the most deadly dendrobatid frog with enough toxin in one frog to kill 20,000 lab mice. Touching it can be fatal to a human, especially if the toxins get into the bloodstream through a laceration in the skin. The frogs do not have poison glands on their feet.
The alkaloid toxins affect muscles and nerves, many times causing respiratory and heart failure. The Choco Indians of western Columbia use these frogs in hunting by placing the toxins on the tips of arrows or darts. The tribes boil the frogs and then dip the darts in the poison, or they hang the frogs over a fire by forcing a sharp stick into their mouths. The heat causes the poison to moisten the back of the frog in the form of a white froth, making it easy to get on the tip of a dart. One frog can produce enough toxin to coat 50-100 arrows, and the darts remain toxic for about a year. The indians use the darts to kill spider and howler monkeys, as well as other small animals. The batrachotoxin, the most toxic of the alkaloids, can aid in the hunting of jaguars, deer, and birds. Frogs of the species Phyllobates terribilis do not have to be killed for their poison. The indians just rub the darts on their backs and the poison is secreted. Studies of the toxins from different species have shown that frogs of similar species have vastly different alkaloid chemicals.
Research has found about 300 new alkaloids in dendrobatid frogs. Batrachotoxin has allowed scientists to study sodium channels, which are responsible for regulating the excitation of nerve cells. Other toxins help us to understand more about how local anesthetics work. Epibatidine, one alkaloid chemical, has been proven to numb more efficiently than morphine. Better anesthetics are always being sought out to decrease the rick of post- anesthetic problems. Pharmaceutical research has also looked at the uses of these new toxins as muscle relaxants, heart stimulants, heart regulators, and anesthetics.
Unfortunately, research on the possibilities of the dendrobatid frogs' secretions is limited because these frogs are currently on the threatened list due to the rapid destruction of their habitats. Obtaining these species is getting difficult because frogs in captivity seem to loose their toxic secretions probably due to environmental and dietary changes. Scientists have recently been exploring the possible link between the frogs' diet of ants and the ability to produce alkaloid poisons. More alkaloids are found in ant species than in any other group of insects, and it has been observed that ants comprise from 50-73% of the Dendrobatid frogs' diet. Further research has shown that other non-toxic frog species have diets with only about 12-16% ants. The consumption of ants that contain alkaloid compounds may be the primary character that led to the development of toxic skin and the radiation of poisonous species. Researchers are now trying to find ways of raising ant species to feed frogs in captivity in hopes that someday the captive frogs can produce enough alkaloid substances for more substancial findings. Without these toxins being produced in large accessible quantities, research can be minimal at best.
Without measures to protect their natural habitats, the dendrobatid frogs may become extinct. Their extinction will decrease the diversity of animal life and prevent many new chemicals from being discovered. These new chemicals could provide biomedical researchers with information that will help to develop drugs that can be extremely important to humans. Saving the frogs' natural habitat will prove to be beneficial to everyone. Who knows....one day, your life may literally be saved by a frog!
The pictures and information that are represented in this page were compiled from the many helpful webpages dedicated to Dendrobatid Frogs. A special thanks goes to the Frogs! page for the wonderful pictures. To see my sources right click on the picture and the URL of the picture will appear. All materials used are for informational purposes and are not intended for any commercial use.