The same scientific background and love of the outdoors/wildlife that prompted me to volunteer at the Canadian Museum of Nature provoked my curiosity about frogs. After viewing the exhibition Frogs – A Chorus of Colours, I wondered how such a variety of physical characteristics afforded protection for each of the species.
In particular, frogs tend to be well camouflaged. There are the ornate horned frogs, for example, which blend with shadows, grasses and leaves, and the African bull frogs, which are camouflaged among wet rocks and leaves.
In contrast to these species, the dramatic markings and bright colours of the poison-dart frogs are truly remarkable. The diversity within the frog family, and in particular the beautiful and dangerous poison-dart frogs, encouraged me to learn more.
Canadian frog species were fresh on my mind thanks to a late-summer vacation in Algonquin Park with my family. On our hikes, we were looking to find wildlife and found many frogs. We knew that they were there because we heard the croaking, but it took some time to find them among the swampy waters surrounding Peck Lake. Like all native frogs in Canada, the frogs were camouflaged in their natural habitat, protecting them from predators.
Poison-Dart Frogs of South and Central America
In contrast, there are brightly coloured yellow, orange, purple, red and blue frogs living in the rainforests of the world—a few of which you can see in Frogs – A Chorus of Colours. These include the poison-dart frogs of South and Central America, which belong to the Dendrobatidae family. These tiny, beautiful frogs have a very special slime on their skin that contains the potentially lethal toxins that they are named for.
Although it is understandable why camouflage protects frogs in the wilderness, it is not entirely obvious why bright skin colouring also protects them. It does so in a couple of ways.
First, while these frogs are poisonous, not all species from the Dendrobatidae family are deadly. The poison can cause serious swelling, nausea and muscular paralysis. A predator that survives its first encounter with such a frog will recall its bright warning colours, its dreadful taste and the after-effects of the meal. The variation in frog toxicity (from nausea to death) is likely an important factor in the equation. This mechanism can protect an entire local frog population after a single predator-prey interaction.
Second, as mentioned, while each species of wild poison-dart frogs is poisonous, the toxicity varies among the ~175 species and their different geographic populations. Among these is the genus Phyllobates, which contains the golden poison frog Phyllobates terribilis—a very fitting name for the most poisonous of the frogs. Some have indicated that the slime from a single golden poison frog contains enough poison to kill 10 people! Reportedly, for making their infamous deadly hunting darts, the native tribes of South America use only four frog species, all from the genus Phyllobates.
Interestingly, evolution has favoured a snake species (Leimadophis epinephelus) that has immunity to the poison-dart frog toxins, and these snakes actually feed on them.
You Are What You Eat, Especially If You Are a Frog
The diet-toxicity hypothesis describes the reason behind the toxicity of these frogs. The poison-dart frogs do not synthesize these poisons themselves, but rather, they consume arthropods (e.g., ants and centipedes) and secrete the toxins gathered from these prey in the slime on their skin. In agreement with this theory, poison-dart frogs raised in captivity do not possess significant toxicity because of their controlled diets. Captivity-raised frogs retain their ability to accumulate these toxins; upon returning to their native habitat, they will once again become poisonous.
Another species of poison-dart frog includes the phantasmal poison frog (Epipedobates tricolor). Although these frogs also secrete lethal toxins into the slime on their skin, a chemical has been extracted and has been found to have a potential medicinal use. Epibatidine is a painkiller that is 200 times as potent as morphine. Unfortunately, its therapeutic concentration is very close to its toxic dose, which means that its therapeutic window is too small for practical use! Other compounds isolated from other species in the Dendrobatidae family have been studied as muscle relaxants and heart stimulants.
See Them at the Museum
Poison-dart frogs are only a few of the amazing frogs that you will encounter in Frogs – A Chorus of Colours. This wonderful presentation includes other activities, including mini-golf with a frog-predator theme, and an origami-frog craft.