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Evolution resulted in an endless variety of adaptations to two basic aspects of life: feeding and defense.
Elephants, for example, have very obvious adaptations--the trunk and the tusk--for feeding and defense. Other groups of animals, like hermit crabs, occupy gastropod shells as a form of protection. Spiny-tailed geckos in Australia cannot close their eyelids, but since the eye is one of the most vulnerable parts of their bodies and has to be protected, the eye has the same coloration and same pattern as the rest of the body so it will be hard to detect. These examples--and there are an endless number of similar examples in the animal kingdom--are macroscopic, morphological means to cope with feeding and defense.
Snakes and a large variety of other animal groups developed a strategy to cope with feeding and defense by primarily molecular means: the evolution of venoms and poisons.
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Venoms vs. Poisons |
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Generally, a poison is a toxic substance that is distributed throughout the tissues of an animal's body. These animals lack any specific or localized apparatus for producing, storing or delivering poisons. Instead, the whole body, or large parts of it, is toxic. Typical poisonous animals are frogs, newts and jellyfishes.
Contrary to poisons, venoms of animals are produced, stored and delivered by a very specific set of organs, and venoms are not distributed freely in other tissues of the animal body. Typical venomous animals are the venomous snakes, scorpions and cone shells.
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Going quickly through the animal kingdom, you see venomous and poisonous creatures from the very simple organisms up to the higher vertebrates. The box jellyfish of Queensland is one of the most potent poisonous jellyfishes. Around February, when box jellyfish come close to the shore, people are discouraged from going swimming at the beaches, and are advised to swim in large enclosures so that they are protected from possible poisoning by the jellyfish.
There are poisonous species among corals. One of the most potent toxins against acetylcholine receptors, which play an important role in neuromuscular transmission, has been isolated from corals. An extremely venomous animal is the cone shell, of which there are approximately 600 species. All of them are venomous, but only a dozen or so of them are really life-threatening to humans. They have all kinds of toxins that act on nerve cells as well as muscle cells. I will go into this in more detail a little bit later.
There are plenty of other examples of venomous and poisonous species from the marine environment. Sea anemones have toxins inhibiting the function of sodium channels, which play an important role in the action potential of nerve and muscle cells. Some of the sea urchins and sea stars also produce potent toxins. Fishes of many types can be poisonous or venomous, including the puffer fish, turkey fish and stonefish.
In amphibians, the poison arrow frogs of Central and South America have very potent poisons. Some Indian tribes in South America use the toxins from these frogs to poison the end of their darts, which they use in blowguns for everyday hunting.
In reptiles, there are venomous lizards living in the southwestern United States and northern Central America, all the way down to southern Guatemala. There are a large number of venomous species among the different kinds of scorpions and spiders, of course, as well as snakes.
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