title: Reverse evolution of armor plates in the threespine stickleback.
abstract: 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.
authors.affiliation: Division of Human Biology, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109.
authors.forename: Jun
authors.initials: J
authors.lastname: Kitano
authors.affiliation: Section of Integrative Biology, University of Texas, Austin, Texas 78712.
authors.forename: Daniel I
authors.initials: DI
authors.lastname: Bolnick
authors.affiliation: U.S. Geological Survey, Washington Cooperative Fish & Wildlife Research Unit, School of Aquatic and Fisheries Sciences, University of Washington, Seattle, Washington 98105.
authors.forename: David A
authors.initials: DA
authors.lastname: Beauchamp
authors.affiliation: U.S. Geological Survey, Washington Cooperative Fish & Wildlife Research Unit, School of Aquatic and Fisheries Sciences, University of Washington, Seattle, Washington 98105.
authors.forename: Michael M
authors.initials: MM
authors.lastname: Mazur
authors.affiliation: Biological Laboratory, Gifu-keizai University, Ogaki, Gifu 503-8550, Japan.
authors.forename: Seiichi
authors.initials: S
authors.lastname: Mori
authors.affiliation: Research Department, Research Institute for Humanity and Nature, 335 Takashima-cho, Kamigyo-ku, Kyoto 602-0878, Japan.
authors.forename: Takanori
authors.initials: T
authors.lastname: Nakano
authors.affiliation: Division of Human Biology, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109. Electronic address: cpeichel@fhcrc.org.
authors.forename: Catherine L
authors.initials: CL
authors.lastname: Peichel
mesh_terms: D000220:Adaptation, Biological; D000818:Animals; D005075:Biological Evolution; D017753:Ecosystem; D053331:Ectodysplasins / Q000235:genetics*; D051456:Gene Flow; D011235:Predatory Behavior; D012641:Selection, Genetic; D023701:Smegmamorpha / Q000033:anatomy & histology* / Q000235:genetics; D014337:Trout; D014861:Washington
chemical_list: D053331:Ectodysplasins