New Horizons in the Biology of Plant Defenses

Abstract

The answer to Why do "all the good things which an animal likes have the wrong sort of swallow or too many spikes"? (Milne, 1928) is that the herbivores selected the plants to be that way. Given the acceptance of this answer, there appears to be no more intellectual content to be discovered in the study of the biology of secondary compounds. There appears to be only the working out of the detailed mechanics of how secondary compounds are made, what they cost, how they affect an herbivore, how they are avoided, how they are genetically programmed, etc. However, once Darwinian selection became linked with genetics, the same could be said for all areas of evolutionary biology. So do we pack up and go home? No, I vote for absorption in the challenge of figuring out the details of how systems work, systems that are by and large invisible to us because we are too large, because we cannot go back in time, or because our presence stops the system. I cannot watch a cell construct a morphine molecule, I cannot see how a mastodon responded to a Simaba cedron fruit 15,000 years ago, and I cannot watch an agouti eating wild seeds since it refuses to eat when I approach it in the rain forest. There are new horizons in the biology of secondary compounds that are of great importance in understanding human feeding and medical biology and involve multiple intricate puzzles about how animals and plants interact. After all, herbivores are responsible for the caffeine in your morning coffee, the tannin to make leather shoes, and synthetic pesticides in the environment. It is my intent in this chapter to underline some areas of research in plant defense biology where major questions are seemingly being ignored or the major questions do not seem to correspond to observations in the field.