P. terribilis 'Yellow'

Phyllobates

Dumeril and Bibron, 1841

Etymology
Phyllo: Contemporary Greek for “leaf”; bates: From Greek, meaning to “to walk or climb”

Range
Central America (throughout Nicaragua, Costa Rica and Panama) and South America (western and northwestern Colombia)

The Genus Phyllobates contains five species:  P. aurotaenia, P. bicolor, P. lugubris, P. terribilis, and P. vittatus.  Three of these, P. terribilis, bicolor and aurotaenia, are famously used by some indigenous peoples of Colombia (The Chocó and the Cofán) to poison the tips of hunting darts.  Of these three, P. terribilis is the most lethal, producing up to 1900mgs of toxin per frog (enough to kill 20,000 mice, 10 human adults, or 2 large elephants) compared to an average of 47mgs per frog for both P. bicolor and P. aurotaenia.  When P. terribilis is used the darts are rubbed over the skin of the live frog to collect the poison.  P. bicolor and P. aurotaenia are impaled on sticks and often held over a flame to maximize the amount of toxic secretions. The poisoned darts are then used for hunting.[1]  Once treated, the darts can remain deadly for more than 3 years.

All five species of Phyllobates produce batrachotoxins; however, P. vittatus and P. lugubris do so at much lower levels.  This is likely sufficient to discourage predation.  According to Myers et al., “… tasting the back of P. vittatus gave the human taster a sensation of near-numbness of the tongue, followed by a distinctly unpleasant tightening in the throat.”  One might imagine that the effects would be greater on a smaller predator, a bird for example, if it were to consume the entire frog.

Recent studies indicate that the genus Phyllobates is represented by two distinct lineages. One Central American (P. lugubris and vittatus), and the other South American (P. aurotaenia, bicolor and terribilis).  Studies suggest the ancestral arrival of Phyllobates into Central America from South America as early as the Paleocene (between 65 and 54.8 million years ago). Geographic separation, specifically the uplift of the Cordillera Central mountain range during the Miocene (between 24 and 5.3 million years ago) is the suspected driver of speciation.[2]

It can be seen that a game of “one-upmanship” is continually at play in nature; therefore, it is logical that the Central and South American lineages maintain toxicity levels relative to the predation pressures of their respective environments.  For example, the one snake known to prey upon P. terribilis, Liophis epinephelus, is endemic throughout Amazonian rainforests. It has developed a resistance – not a fail-safe immunity to the frog’s toxins.  In this particular match P. terribilis is slightly ahead, as not all of these snakes can survive eating a fully-charged adult frog. Those that do will pass on the gene for increased immunity to batrachotoxins, and so it goes. Perhaps  L. epinephelus does not have a significant presence in Central America, and therefore the Central American Phyllobates would not need to maintain the toxicity levels of their southern cousins. Nature has no doubt provided them with similar predator-culling abilities, locking them in their own evolutionary race.



[1] Myers eta al 1978

[2] Widmer et al. A Molecular Phylogenic Analysis of the Neo-tropical Dart-Poison Frog Genus Phyllobates (Amphibia: Dendrobatidae)