A Chemical Distress Signal

J. H. Tumlinson and colleagues at the U.S. Department of Agriculture's Research Service Laboratories in Gainesville, Florida, have explored a fascinating case that illustrates the intricacy of many ecological relationships. Cotton plants, like many other crops, are attacked by caterpillars. One destructive cotton pest, the army worm, produces a complex series of reactions when it feeds on the plant—a reaction that involves the caterpillar itself, the tissues of the plant, and a third participant, a wasp that preys on the caterpillar. When the caterpillar chews on the cotton plant leaf, a reaction occurs that causes the plant to synthesize and release a class of volatile chemicals that escape into the air and travel rapidly downwind. The chemicals are detected by wasps, who follow the scent

and are able to find the caterpillars and deposit eggs within them. The eggs hatch, and the wasp larvae destroy the caterpillar.8

This complex case of "chemical ecology" required a series of linked coevolutionary events: the response of the plant to a special signal from its predator, and the response of the wasp to a special signal from the host of its prey.

plants manufacture and store chemicals that deter herbivorous insects; but usually one or more insect species will have evolved biochemical mechanisms for inactivating the deterrent, providing them with a plant they can eat relatively free of competitors.

Another classic example of coevolution involves the introduction of rabbits and the myxomatosis virus into Australia. After rabbits were brought to Australia, they multiplied rapidly and threatened the wool industry because they grazed on the same plants as sheep. To control the rabbit population, a virulent pathogen of rabbits, the myxomatosis virus, also was introduced into Australia. Within a decade, rabbits had become more resistant to the virus, and the virus had evolved into a less virulent form, allowing both the host and pathogen to coexist.9

Conclusion

As the examples in this chapter demonstrate, evolutionary biology provides an extremely active and rich source of new insights into the world. By exploring the history of life on earth and shedding light on how evolution works, evolutionary biology is linking fundamental scientific research to knowledge needed to meet important societal needs, including the preservation of our environment. Few other ideas in science have had such a far-reaching impact on our thinking about ourselves and how we relate to the world.

NOTES

1.  

Biological Sciences Curriculum Study. 1978. Biology Teachers' Handbook. 3rd ed. William V. Mayer, ed. New York: John Wiley and Sons.

2.  

Francois Jacob. June 10, 1977. Evolution and tinkering. Science 196:1161-1166.

3.  

National Academy of Sciences. (in press). Science and Creationism: A View from the National Academy of Sciences. Washington, DC: National Academy Press. (See www.nap.edu)

4.  

P. Ewald. 1994. The Evolution of Infectious Disease. New York: Oxford University Press.

5.  

"Evolution, Science, and Society: A White Paper on Behalf of the Field of Evolutionary Biology," Draft, June 4, 1997.

6.  

Jonathan Weiner. 1994. The Beak of the Finch. New York: Alfred A. Knopf.

7.  

Peter R. Grant. 1991. Natural selection and Darwin's finches. Scientific American, October, pp. 82-87.

8.  

James H. Tumlinson, W. Joe Lewis, and Louise E. M. Vet. 1993. How parasitic wasps find their hosts. Scientific American, March, pp. 100-106.

9.  

F. Fenner and F.N. Ratcliffe. 1965. Myxomatosis. Cambridge: Cambridge University Press.



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