Upon walking into the forest on the island
of Bastimentos in the Bocas del Toro Archipelago
in the wet season, one is struck by a cacophony
of rather non-musical chirping that sounds
like it must be coming from a hoard of crickets.
Upon closer inspection however, you will be
surprised to find that this harsh noise is
coming not from an insect, but from a small
frog.
Despite their small size, you will have no trouble in locating these tiny frogs, because their entire bodies are an intense red color, sometimes with and sometimes without black spots. These frogs are called strawberry poison frogs (or on Bastimentos, simply "red frogs"). They are members of a large family of poison frogs found only in Central and South America, called dendrobatids.
In general, poison frogs are very brightly colored. This bright coloration is apparently a warning to potential predators that the frogs carry very nasty toxins. These toxins are so nasty and so novel, in fact, that they have attracted the attention of a host of biochemists worldwide, who are interested in figuring out how they work, and whether they might have practical uses for human medicine. These efforts recently bore fruit for one toxin called epabatidine (derived from a poison frog called Epipedobates tricolor), which has been converted into a pain killing drug through a bit of clever biochemical manipulation. This pain killing alkaloid is so effective that it is two hundred times more powerful than morphine.
The red frogs which you can see calling on Bastimentos are, of course, males. They are out and about trying to attract a mate. Females are very choosy about mating in this species because they put a lot of time and effort into producing each offspring. In addition to producing nutrient rich eggs, they also take very good care of each offspring they produce. The eggs are laid in the leaf litter, but when they hatch into tadpoles their mother carries them one at a time to plants which have small pools in their leaf axils (like bromeliads). There the mother places the tadpole (one tadpole to a pool), but she is not done yet. She will come back to each pool periodically over the next several months to feed her offspring. She does this by backing into the pool and depositing an infertile egg. This nutrient rich package makes a nice meal for the tadpole, and in fact these small pools are so nutrient poor that the tadpoles can't grow or survive without getting food from their mother in this way. The tadpoles even beg for food when a frog approaches: they will come up to the surface and vibrate their tails in a special way, signalling "I'm hungry"! But mothers won't feed just any tadpole: they remember each pool where they have placed their own offspring, and go back to those specific pools, ignoring the begging vibrations of tadpoles from other mothers in nearby pools.
Once you have seen the red frogs on Bastimentos, you might go and look for similar frogs in other parts of the Bocas del Toro Archipelago. When you find them, you will be in for a shock. Because in other parts of the archipelago, these same little frogs (with the same insect-like chirp), will be a completely different color! For example, if you go to Pope Island, you will find not red, but green frogs making this chirping noise. If you go to Cerro Brujo, you will find dark blue frogs. If you go to Nancy Key, you will find bright orange frogs. If you go to Bocas Island, you will find green and yellow frogs with black polka-dots. Each separate population of these little frogs seems to have its own distinctive color and pattern. The reason for this explosion of color and pattern in these different populations is not known. It doesn't appear to have anything to do with how toxic they are: some of the most toxic populations have quite dark coloration. It also doesn't seem to be related to high levels of genetic divergence: recent research shows very low levels of genetic divergence among populations in the archipelago. Whatever caused this dramatic divergence, it was fast: geological evidence shows that the Bocas del Toro Archipelago has only been in existence for around 5,000 to 10,000 years, the mere blink of an eye in evolutionary terms. Scientists are now actively investigating these fascinating frogs for clues as to why there has been so much divergence in color and pattern between different populations in the archipelago.
Written by Kyle Summers
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