A new study carried in Madagascar has showed that poison frogs are losing their toxicity as human activity fragments their habitats.

Poison frogs are, in fact, two distinct evolutionary lineages: one group (Dendrobatidae) (one dendrobatid in photo bellow) lives in tropical wet Central and South America and are more closely related to true toads and the other group (Mantellidae) (one mantellid in photo above) lives in Madagascar Island and is more close to true frogs.

These convergent groups share some similarities: they are brightly colored with awesome models (aposematical coloration warning predators), small (many are specialized ant eating) and store alkaloids on their skin. Alkaloids are nitrogenous toxic substances synthesized by plants (some well known alkaloids are caffeine, nicotine, cocaine) which are have a bitter taste and lethal in various doses.

These frogs ingest alkaloids with their food (primarily from ants which store them from plants) and these are accumulated in their skin, which makes the animals venomous to potential predators. "It gives them a nice defense, and they don't have to waste energy biosynthesizing and making [the toxins] on their own." said Valerie C. Clark, a graduate student in chemistry at Cornell University in Ithaca, New York. "And they're stealing it from their diet, which means they are also able to eat toxic insects other frogs reject as distasteful," she added. "They're able to exploit a whole other niche."

Interestingly enough, some alkaloids are found both in Malagasy and American poison frogs, even if neither the frogs nor their prey are related. "We looked at only a limited number of sites but found that frog individuals have more different alkaloids at pristine sites and less at fragmented sites," said Clark.

"While individual alkaloids vary in their toxicity, frogs with a greater variety of the chemicals in their skin are more likely to pack a lethal punch to their predators," said Clark.

Scientists still don't know if frogs need a certain number of alkaloids to keep them venomous. "If the answer is yes, some of Madagascar's poison frogs may become defenseless as human development breaks up their habitats," Clark says.

The team found 30 alkaloids for frogs from pristine forests, 12 for frogs from forested patches around cultivated fields, while in a moderately disturbed environment, along a road side, they scored with 15.

"This could be a reflection of the arthropod diversity at these sites," Clark said.

Man induced habitat fragmentation could lead to an alteration of the ecology and distribution of poison frogs. When the frogs lose toxicity, the brightly colored defenseless frogs will be easy targets for predators learning there's nothing to fear on attacking them. "In addition, Clark says, the frogs may abandon habitats that lack sufficient alkaloid-containing ants, affecting distribution."

Scientists warn that alkaloids found in poison frogs' skin may prove to be important in human medicine and we should be more active in protecting these animals.

In the early 90's, Abbott Labs created ABT-594, a non-toxic, non-addictive painkiller from poison frog skin, potentially effective for treating several types of pain. Unlike an opiate, ABT-594 promotes alertness instead of sleepiness and has no side effects on respiration or digestion.

This find nearly did not happen as the area of Ecuadorian rainforest, habitat of the frog observed in the study, was cleared in the '80s for banana plantations. Luckily, a second site still housed the frogs and researchers could collect a sample of the poison which would later serve for the research.

A team at the National Institute of Diabetes and Digestive and Kidney Diseases in Bethesda, Maryland has recently reported an alkaloid, called 251D, from poison frog skin, that wards off mosquitoes and flies. "This compound will never have useful purpose as a mosquito repellant. It would probably be too toxic to mammals such as ourselves. Instead, the researchers are pursuing potential applications of the compound to help treat autoimmune diseases," said John Daly, an expert in identifying bioactive alkaloids in poison frogs.

This team discovered another path of how human activities affect poison frogs. As agricultural inroads have increased, an unusual alkaloid appeared and became a major frog-skin alkaloid in only ten years in frogs from a small Panamanian island. A small millipede was the source of that alkaloid.