In a paper published in last week’s Nature, researchers have identified a toxin in the venom of the Texan coral snake (Micrurus tener tener) that directly induces pain in bite victims. The toxin, known as MitTx, has been observed to activate specific signalling macromolecules called acid-sensing ion channels (ASICs). Further, venom from the second coral snake species included in the research (M. frontalis) also activated a similar group of neurons.
What is so interesting about this novel property of snake venom is the ecology of the species from which it is produced: New World coral snakes (genera Leptomicrurus, Micruroides and Micrurus) exhibit aposematic (warning) colouration of varying degrees. Both species in the study possess the red/yellow/black banding typically associated with coral snakes, and the pattern is shared by numerous nonvenomous and mildly-venomous snake species found throughout the entire range of coral snakes, although which group of snakes is mimicking which is poorly understood. However, the discovery of pain-inducing properties of coral snake venom could provide insights into the evolutionary significance of coral snake colouration, and possibly explain the mystery of who is mimicking whom.
If pain-producing toxins prove to be widespread in the venom of coral snakes with aposematic colouration, and absent in closely-related or sympatric venomous snakes that lack such patterns, it would suggest that the bright colours may have evolved as a conspicuous signal for predators to associate with the excessive pain of a coral snake bite. This, in turn, would then indicate that the occurrence of similar colour patterns in less dangerous sympatric snakes is due to selection favouring a resemblance to venomous coral snakes, or Batesian mimicry; the harmless species exploit the capability of predators to recognise the pattern of unpalatable and dangerous species, thus lowering the predation pressure on the harmless species.There are, of course, some potential deal-breakers for this possible explanation to a long-studied phenomenon. As mentioned above, the presence of the toxin in numerous species that do not have aposematic colouration would suggest the evolution of aposematism in coral snakes was not exclusively linked to the possession of a particularly painful bite. Further, the research was in vitro, using the neuronal system of rodents, whereas the natural predators of coral snakes (mainly birds and other snakes) may exhibit different reactions to the toxins.
Either way – whether or not this toxin can provide greater insights into the evolutionary history of one of the most iconic snake colourations worldwide – the presence of such toxins in snake venom raises numerous lines of further research regarding the nature of predator-prey interactions.
Bohlen, CJ. et al. 2011. A heteromeric Texas coral snake toxin targets acid-sensing ion channels to produce pain. Nature 479(17th November 2011):410-414.
Image from Wikipedia.