Um quebra-cabeças evolutivo não resolvido: a evolução das toxinas natuRais

segunda-feira, fevereiro 14, 2011


Toxins and venoms

Edmund D. Brodie III

The macabre human fascination with natural toxins is age-old, but practical. From the eyes of newt and toads tossed in the cauldron of the witches of Macbeth, to the ‘swamp adder’ that serves as a near-perfect murder weapon in Doyle’s The Speckled Band, poisonous creatures captivate people’s imaginations precisely because they are so dangerous. Nonetheless, some of the most dramatic mysteries regarding natural poisons concern the evolutionary forces and processes that are responsible for the staggering diversity of compounds, delivery systems and organisms by which toxins and venoms take the stage.

Natural toxins can be found in virtually every major group of organisms, from fungi to mammals, from bacteria to birds. The actions of these poisons range from disrupting digestive processes to binding and blocking a single voltage-gated ion channel in a specific tissue. Some organisms seem to possess only a 
single toxic compound whereas others produce a whole cocktail of drugs with varying targets and effects. Some compounds are found in identical form in as many as five different phyla. A major challenge to understanding the biology of toxins is recognizing that many phenomena are artificially pooled under a single term.



"One of the most puzzling paradoxes in the evolution of toxins is why organisms evolve to be deadly — contrary to venoms, for which deadly effects have a clear benefit. Extreme toxicity occurs repeatedly, from saturniid caterpillars to dart poison frogs. Selection favors the most-fit individuals, and those should be the ones that avoid predation. Killing an individual predator does not give an advantage over simply deterring one, especially if the prey has to be handled or eaten by a predator to deliver the poison. How, then, can we explain the evolution of deadly toxicity?" (Brodie, E. D., III. 2009. Toxins and venoms. Current Biology 19: R931-R935).



Brodie é um especialista respeitado nesta área científica. Quaisquer questionamentos, críticas ou sugestões podem ser enviados a ele no e-mail que aparece no fim do seu artigo.