The Natural History and Taxonomy of the Blue Poison Frog, Dendrobates azureus (tinctorius)

A recent American Museum of Natural History sponsored review of poison frog taxonomy revealed this frog to be a local color morph of the dyeing poison frog, Dendrobates tinctorius, and not a separate species. The scientific name D. azureus is, therefore, no longer recognized by herpetologists. The blue dart frog varies so much in appearance from the dyeing dart frog that many find this information difficult to accept, and so the name D. azureus is still much used. Other quite variable color phases and races of the dyeing poison frog range throughout the lowland forests of French Guiana, Guyana and adjacent areas of Brazil.

Physical Description
The term “electric blue” is often used to describe this frog’s background color, and certainly there is some justification in that. The blue poison frog really must be seen if one is to get a sense of its appearance, as words cannot convey the over-all effect of the startling mix of colors. The body and head are sky-blue spotted with black, while the arms and legs are a brilliant dark blue. Males have wider front foot toe pads than do females, and are a bit thinner in build. Otherwise, the sexes are quite difficult to distinguish. Blue poison frogs average 1.5 to 1.8 inches in length.

Range and Habitat
The blue poison frog has an extremely limited natural range, being known only from the Sipaliwini Savannah on the western slope of the Vier Gebroeders Mountain in south-central Suriname (on the northern coast of South America).

It inhabits fragments of moist forest within a dry savannah (grassland) at approximately 1,150 feet above sea level. This area was most likely covered by trees in the past – as the habitat changed to grassland the frog became isolated those few, tiny patches of forest that persisted. Blue poison frogs live on land in the vicinity of running streams (they do not swim) and occasionally climb trees to heights of 20 feet or so.

Status in the Wild
Despite a great deal of scientific and pet trade interest in this species, its status in the wild has not been well-documented. The species’ continued existence is jeopardized by its tiny natural range and the threat that forest fires from farming activities will destroy what little habitat remains.

The blue poison frog is classified as “Vulnerable” by the IUCN, listed on CITES Appendix II and protected by the government of Suriname. Fortunately, it is frequently bred by hobbyists and in zoos. Inbreeding may, however, be a concern in the future, as new animals have not been legally collected for the pet trade in some time (illegal collecting is thought to occur). Herpetologists from the National Aquarium in Baltimore have received permission to bring new animals into captivity.

Diet
In common with other poison frogs, this species feeds mainly upon ants and termites (those I have kept preferred these to all other foods), but also takes tiny spiders, millipedes, springtails, beetles and other small invertebrates found in leaf litter.

Reproduction
Males call from below fallen leaves and other protected sites on land. In contrast to many frogs, female blue poison frogs actively court the males by stroking the snout and back. Females lay 2-6 eggs in a hollow below leaves, fallen logs or in similar moist, protected locations, after which they are fertilized by the male. The eggs are tended by the male, and sometimes by the female as well. Males soak in water and then lie over the eggs to moisten them, and may tend several clutches at once. The eggs hatch in 14-18 days and the tadpoles are transported to streams on the back of either parent. The tadpoles feed upon algae, decaying plants, Daphnia, mosquito larvae and other small, aquatic invertebrates and each other, and transform into frogs in 70-85 days.

Miscellaneous
The taxonomy of the family to which this species belongs, Dendrobatidae, is quite confusing due to the widely differing appearances of individual frogs of the same species (i.e. the blue and dyeing poison frogs). Also, captive poison frogs of different species, subspecies and populations readily interbreed, raising the possibility that such may occur in the wild as well. There are now considered to be 5 species of frogs within the genus Dendrobates, and 164 species within the family Dendrobatidae.

The blue poison frog and its relatives secrete virulent skin toxins (histrionicotoxins, pumiliotoxins and others) when disturbed. Originally, these toxins were thought to occur naturally within the frogs, in the manner of snake venom. However, tests at the National Aquarium in Baltimore and elsewhere revealed that some captive poison frogs were lacking in skin toxins. However, the same frogs, when released into an indoor “rainforest” at the Aquarium, soon developed the toxins. Subsequent research revealed that these unique chemicals are derived from alkaloids harbored by certain ants and millipedes (and possibly other invertebrates) that the frogs prey upon. Frogs consuming the standard captive diet of fruit flies and crickets soon lost their toxins and were unable to synthesize others.

The skin secretions of 3 poison frog species belonging to the genus Phyllobates were harvested by the Mucushi, Chaco and possibly other people in Columbia, South America for use on hunting darts (contrary to popular belief, frog toxin use in warfare has not been documented). These species, the golden poison frog, P. terribilis, the bi-colored poison frog, P. bicolor, and the Kokoe poison frog, P. aurotaenia utilize secretions, known as batrachotoxins, which differ from those in the skins of Dendrobatid frogs. Batrachotoxins have only been identified in these 3 frogs and, oddly enough, in 2 birds native to New Guinea. Batrachotoxins cause heart failure by suppressing nerve impulses. A single 2 inch long golden poison frog harbors enough of these chemicals to kill 10-20 people.

The skin toxins of the blue poison frog and related species are highly complex and are being studied with a view towards developing medications that may be useful in oncology and infectious disease research and treatment. One compound derived from the secretions of the phantasmal poison frog, Epipedobates tricolor, shows great promise as a pain medication – more effective than morphine, it is both non-addictive and non-sedating.

The use of frog toxins on hunting darts was first reported in the literature in 1823, by British naval captain C. Cochrane. He observed golden poison frogs to be confined and fed by their captors until their skin secretions were needed. The chosen frog was then pierced with a stick in order to induce the secretion of the toxins, which appear as a white froth on the skin. Up to 50 darts could be treated with the secretions from a single frog, and the darts were reported to retain their potency for up to 1 year. A jaguar shot with a dart so treated was said to die within 4-5 minutes, with smaller animals being killed instantly.

An interesting article concerning the complex breeding behaviors of various poison frogs is posted at:
http://animals.jrank.org/pages/148/Poison-Frogs-Dendrobatidae-BEHAVIOR-REPRODUCTION.html