December 29, 2005 | David F. Coppedge

Evolutionary “Arms Race” – Is Coevolution Relentless?

Camellias and the weevils that attack their seeds seem locked in conflict.  The thicker a camellia grows its protective woody covering around its seeds, the longer the feeding tube on some weevil to break through and devour.  John R. Thompson talked about such “coevolutionary arms races” in Current Biology1 and asked whether such wars can go on forever, leading to increased exaggeration of traits.
    The answer is, apparently, there are limits.  Traits vary in a mosaic pattern across populations.  Not all camellias are infested by beetles with the longest boring tools.  As with any war, there are hotspots and coldspots.  The dynamics of arms races seem to buffer both species against extremes.

Collectively, these studies suggest that coevolution is a pervasive process that continually reshapes interspecific interactions across broad geographic areas.  And that has important implications for our understanding of the role of coevolution in fields ranging from epidemiology to conservation biology.  Many diseases, for example malaria, vary geographically both in parasite virulence and host resistance, potentially creating regions of coevolutionary hotspots and coldspots.  The spread of introduced species seems be creating new geographic mosaics of coevolution as some species become invasive and coevolve with native species in different ways in different regions or drive rapid evolution in native species, sometimes in less than a hundred years or so.  The results for Japanese camellia and camellia weevils reinforce the developing view that interactions coevolve as a geographic mosaic across landscapes, and it is often difficult for one partner to get ahead of the other (or others) everywhere. (Emphasis added.)

1John R. Thompson, “Coevolution: The Geographic Mosaic of Coevolutionary Arms Races,” Current Biology, Volume 15, Issue 24, 24 December 2005, pages R992-R994, doi:10.1016/j.cub.2005.11.046.

This appears to provide more slippage on the evolutionary treadmill (see 03/17/2003 entry).  Though the word “evolution” is involved, don’t be confused; this has nothing to do with macroevolution, like bacteria evolving into people.  Coevolution leads to exaggerated traits between two interacting species, like the beaks of hummingbirds and the flowers they pollinate.  As with all other observed forms of microevolution, including Darwin’s famous finches, it involves the modification of existing traits – not the origin of new ones.
    Notice how quickly changes can result; Thompson referred to rapid “evolution” in native species in less than 100 years after an intruder was introduced.  Young-earth creationists could use such concepts to explain the rapid diversification of varieties and species within created kinds, and there would be nothing Thompson or the Darwinists could do to prove them wrong.  Studies like this do not establish that coevolution can be extrapolated endlessly into macroevolution.  In fact, the quote above seems to indicate otherwise: there are limits to the amount of change in the “coevolutionary arms race.”  World War II did not produce Superman.

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Categories: Terrestrial Zoology

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