MEDIA CONTACT:
Tim Steury, 509/335-1378, [email protected]
John Thompson, 509/335-7466
COEVOLUTION ARGUES FOR PRESERVING LARGE AREAS OF LAND PULLMAN, Wash.--Even as an undergraduate, Washington State University evolutionary ecologist John Thompson was interested in understanding how the enormous diversity of life on earth becomes organized into ecological communities. Now he's an authority on one mechanism: coevolution. In coevolution, species evolve in response to each other. It might happen between a parasite and its host, or between an insect and the plant it pollinates.
"But coevolution is more than just cute little stories," says Thompson. "It's an ongoing process that happens in several different ways." Its role in the organization of ecological communities has been the focus of Thompson's research since graduate school, as well as the topic of the 1997 WSU Distinguished Faculty Address he delivered Wednesday evening on the Pullman campus.
In graduate school, as now, Thompson looked at a variety of different interactions between species -- those between plants and plant-feeding insects and between fruits and fruit-eating birds, for example. Both types of interaction could be looked at in an individual community, but for migratory birds a broader dimension became evident. Along migration routes, many fruit-bearing plants timed their fruiting to the birds' passage. The birds gained food, and the plants gained seed distribution when the birds evacuated their digestive systems prior to taking off. Large geographic areas were obviously important, and they've been part of all questions Thompson's asked since then. By the late 1980s, Thompson had developed the geographic mosaic theory of coevolution, which argues that the long-term dynamics of coevolution occur over large geographic areas rather than within local populations. Much of his current research is directed toward evaluating this theory, his work on Greya moths and the plants they pollinate, for example.
The basic relationship seems simple. Greya moths have elongated abdomens which the females insert through a flower when laying eggs. In the process, pollen that has stuck on the abdomen rubs off and pollinates the plant. When the eggs hatch, the Greya larvae eat a proportion of the developing seeds. The shape of the moth's abdomen and the flower parts it contacts are traits that appear to be specialized by coevolution between them, and they work to benefit both species. Field observations show that local populations of Greya vary in their traits, as do local populations of the plants. This variation has been shown to be genetically determined by laboratory analysis of the DNA of both. This variation is the raw material for coevolution.
If the geographic mosaic theory of coevolution is true, then future work should show that the outcomes of interactions between these species will vary from place to place, since in any given place the local populations of each species are unique. Some of these places will favor coevolution. And finally, there should be evidence that many local populations are connected to each other.
Without these connections, the varied outcomes would be local curiosities and contribute little to the overall evolution of the interaction between the species. The geographic mosaic theory is also being tested in other countries, for other types of interactions and often in collaboration with scientists who hold different perspectives than Thompson.
Thompson collaborated with Jeremy Burdon in Australia on a geographic analysis of Burdon's long term data on coevolution between flax and flax rust. Scientists in Mexico have asked Thompson to help set up a large study of herbivores, pollinators and plants on the Yucatan peninsula. If they can determine the amount of space needed for coevolution of these species, it will help determine the amount of space needed for conservation. And a research group in England is looking at coevolution of fruit flies and parasitic wasps, for they have found that different populations of both species have differing abilities either to defend themselves or overcome those defenses.
"So what?" Thompson would have you ask, "Why is any of this important?" His answer is that we need to understand the geographic scale of coevolution in order to understand the geographic scale necessary for conservation. And what we conserve is often the genetic diversity of species that we need and use each day. "It's yet another argument for preserving large areas of land," says Thompson, which probably pleases this naturalist who became a scientist in order to understand the processes he observed.
--by Mary Aegerter
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