A well known effect in the arms race that ensues between host and parasite, the red queen effect, states that the species that is able to evolve countermeasures faster than its partner will gain the upper hand. New research claims that this is not so when considering mutualistic interactions between species. When deciding who will gain most from the interaction, it pays to move slowly. The quickly evolving species then adapts to the slow evolver's needs.

Mutualistic interactions, in which species provide services to one another, are abundant in nature. Examples are everywhere: from the mitochondria, once free-living bacteria that provide energy from burning sugars with oxygen to every cell in our body, to fungi that enable plants to take up nitrogen from the soil, to ants interacting with caterpillars providing them with protection for food. When such an interaction occurs, who will benefit most? Will the ant benefit most by providing very little protection for a lot of food, or will the caterpillar benefit most by providing very little food for a lot of protection?

Michael Lachmann from the Max Planck Institute for Mathematics in the Sciences in Leipzig and Carl Bergstrom from the University of Washington examined this question by using mathematical analysis. One can abstract the behavior of each species as being "generous" and giving much of the benefit to the other species, or being "selfish" and asking for most of the benefit for itself. In a mutualistic interaction, the two species benefit most from coordinating - when one is "generous" and the other "selfish". Benefits to each are less than optimal in other cases - when both are selfish, or both generous.

When the population of one species is all generous, and of the other all selfish, no evolutionary changes can occur, since no species can benefit from changing its behavior. When pairings of selfish-selfish or generous-generous occur in some cases, then evolutionary change might happe
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Contact: Michael Lachmann
lachmann@mis.mpg.de
49-341-995-9854
Max-Planck-Gesellschaft
17-Jan-2003

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