Using Chemistry to Reconstruct Evolution: On the Origins of Fish-hunting in Venomous Cone Snails

HEMICAL COMPOUNDS derived from living organisms are similar to non-biological substances in that their composition and structure can be characterized, and many can be directly synthesized by standard chemical methods. However, biological compounds are fundamentally different in that each has an underlying evolutionary history. We describe several compounds from an unusual source, the venoms of fish-hunting cone snails. The chemical characterization of some toxins from these venoms has unexpectedly revealed how fish-hunting may have originated in cone snails, and suggests that piscivory may have evolved independently multiple times in these venomous predators. Fish-hunting marine snails would appear to be a most improbable product of evolution. These snails devour fish as their major prey; a priori, fish would be expected to easily elude capture, simply by swimming out of the reach of the snails. However, a significant fraction of the 500 venomous cone snail species (genus Conus ) have evolved to become specialized fish-hunters (Röckel et al. 1995). Cone snails spear their fish prey with a hollow, harpoon-shaped tooth that jets out from a long distensible proboscis; this functions as