Toxins Used as Defenses

We are engineers, and we should remember two things first, there are diminishing returns in trying to get past the 90% point instead of just doing the job, and second, we can always work to change the constraints. 

The biological effects of toxins include damage to an organ system, disruption of a biochemical process, or disturbance of an enzyme activity (Schiefer et al., 1997). Many plants and animals purposefully use toxins to protect themselves against predators and competitors. Thousands of chemicals have been isolated from plant tissues, and many of these serve to defend the plants. Alkaloids are basic organic 

Each of these classes of compounds is used by plants as protection against predators. Tropical plants seem to contain more toxic alkaloids than do temperate species (Molles, 1999). Despite this, tropical herbivores remove approximately ll%-48% of leaf biomass in tropical forests, while in temperate forests they remove only about 8%. This higher level of grazing in tropical areas has apparently produced more intense selection pressure for plants with chemical defenses (see Section 6.17.1). 

Some animals, as well, use toxins to defend themselves. Some poisonous toads and frogs can synthesize toxins. Others acquire their chemical defenses from plants they eat. The Monarch butterfly is probably the best example of this. The larvae eat milkweed leaves and the toxins are retained in their bodies. The toxins are still there after metamorphosis from larva to butterfly. Birds that eat Monarch butterflies regurgitate their prey and quickly learn to avoid others of the same species. 

EVOLUTION AND CYANIDE TOLERANCE (EXCERPTED FROM LANE, 2005) 

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