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Curr Biol. 2008 May 20;18(10):769-774. doi: 10.1016/j.cub.2008.04.027.

Reverse evolution of armor plates in the threespine stickleback.

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Division of Human Biology, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109.
Section of Integrative Biology, University of Texas, Austin, Texas 78712.
U.S. Geological Survey, Washington Cooperative Fish & Wildlife Research Unit, School of Aquatic and Fisheries Sciences, University of Washington, Seattle, Washington 98105.
Biological Laboratory, Gifu-keizai University, Ogaki, Gifu 503-8550, Japan.
Research Department, Research Institute for Humanity and Nature, 335 Takashima-cho, Kamigyo-ku, Kyoto 602-0878, Japan.
Division of Human Biology, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109. Electronic address:


Faced with sudden environmental changes, animals must either adapt to novel environments or go extinct. Thus, study of the mechanisms underlying rapid adaptation is crucial not only for the understanding of natural evolutionary processes but also for the understanding of human-induced evolutionary change, which is an increasingly important problem [1-8]. In the present study, we demonstrate that the frequency of completely plated threespine stickleback fish (Gasterosteus aculeatus) has increased in an urban freshwater lake (Lake Washington, Seattle, Washington) within the last 40 years. This is a dramatic example of "reverse evolution,"[9] because the general evolutionary trajectory is toward armor-plate reduction in freshwater sticklebacks [10]. On the basis of our genetic studies and simulations, we propose that the most likely cause of reverse evolution is increased selection for the completely plated morph, which we suggest could result from higher levels of trout predation after a sudden increase in water transparency during the early 1970s. Rapid evolution was facilitated by the existence of standing allelic variation in Ectodysplasin (Eda), the gene that underlies the major plate-morph locus [11]. The Lake Washington stickleback thus provides a novel example of reverse evolution, which is probably caused by a change in allele frequency at the major plate locus in response to a changing predation regime.

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