Escape and Radiate Coevolution

Escape and radiate coevolution is a multistep process that hypothesizes that an organism under constraints from other organisms will develop new defenses, allowing it to "escape" and then "radiate" into differing species. After a novel defense has been acquired, an organism is able to escape predation and rapidly multiply into new species because of relaxed selective pressure. There are many possible mechanisms available varying between different types of organisms, however they must be novel in order for escape to allow for radiation. This theory applies to predator-prey associations, but is most often applied to plant-herbivore associations. This form of coevolution can be complex but is essential to understanding the vast biological diversity among organisms today. Out of the many forms of coevolution, escape and radiate is most likely responsible for providing the most diversity. This is due to the nature of the "evolutionary arms race" and the continuous cycle of counter adaptations. It is a relatively new field of study and is rapidly gaining credibility. To date, there has not been a formal study published specifically for escape and radiate coevolution.

This theory first originated in "Butterflies and plants: a study in coevolution." (Erlich and Raven, 1964). It outlined and laid the foundations of the concept. However, the term "escape and radiate" was not coined until "Concepts of Coevolution" (Thompson, 1989). The theory has not yet been fully analyzed, however since its origins it has grown in importance among evolutionary biologists, and botanists.

In order for an organism to "escape", and then radiate into varying species it needs a mechanism to escape. These defense mechanisms vary widely and differ for different types of organisms. Plants use chemical defenses in the form of secondary metabolites or allelochemicals. These allelochemicals inhibit the growth, behavior, and health of herbivores, allowing plants to escape. An example of a plant allelochemical are alkaloids that can inhibit protein synthesis in herbivores. Other forms of plant defense include mechanical defenses such as thigmonasty movements which have the plant leaves close in response to tactile stimulation. Indirect mechanisms plant include shedding of plant leaves so less leaves are available which deters herbivores, growth in locations in that are difficult to reach, and even mimicry. For organisms other than plants, examples of defense mechanisms allowing for escape include camouflage, aposematism, heightened senses and physical capabilities, and even defensive behaviors such as feigning death. An example of an organism using one of these defense mechanims is the granular poison frog which defends itself through aposematism. It is important to understand that in order for escape and radiate coevolution to occur, it is necessary that the developed defense is novel rather than previously established.

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