Bergstrom and Lachmann worked with a mathematical model devised from evolutionary game theory, which studies games in which the overall fitness of the players depends on the success each has in playing the game. The model, closely related to models used in the study of economics, can be applied to well-understood relationships between species.
In the case of ants and lycaenids, the largest butterfly family, with many different species, the ants draw considerable benefits by protecting lycaenid caterpillars from parasites that pose a great mortality threat. In return, the caterpillars spend much of their energy producing sugar- and protein-rich excretions as a food source for their ant protectors. The dilemma is how much food should the caterpillars provide and how much should the ants demand. The answer changes over time, depending on how quickly the species evolve. At times the caterpillars might offer less food and at least some of the ants might look for new food sources.
"What the rate of evolution does is tell how long one population can go on taking what's offered," Bergstrom said. "Every time some ants evolve and go off to look for something better, it encourages the caterpillars to offer more. But if the ants don't leave in search of a better deal, eventually they will evolve to accept less.
"Species that evolve fast give in more to pressure than species that evolve slowly."
Bergstrom said the Red King finding is something of an anomaly that will add to the body of knowledge in evolutionary biology.
"I don't think natural selection is going to select for species that evolve slowly. It would be interesting and counterintuitive if that happened, but I don't expect that to happen," he said.
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Contact: Vince Stricherz
vinces@u.washington.edu
206-543-2580
University of Washington
30-Dec-2002