title: Independent axes of genetic variation and parallel evolutionary divergence of opercle bone shape in threespine stickleback.
abstract: Evolution of similar phenotypes in independent populations is often taken as evidence of adaptation to the same fitness optimum. However, the genetic architecture of traits might cause evolution to proceed more often toward particular phenotypes, and less often toward others, independently of the adaptive value of the traits. Freshwater populations of Alaskan threespine stickleback have repeatedly evolved the same distinctive opercle shape after divergence from an oceanic ancestor. Here we demonstrate that this pattern of parallel evolution is widespread, distinguishing oceanic and freshwater populations across the Pacific Coast of North America and Iceland. We test whether this parallel evolution reflects genetic bias by estimating the additive genetic variance-covariance matrix (G) of opercle shape in an Alaskan oceanic (putative ancestral) population. We find significant additive genetic variance for opercle shape and that G has the potential to be biasing, because of the existence of regions of phenotypic space with low additive genetic variation. However, evolution did not occur along major eigenvectors of G, rather it occurred repeatedly in the same directions of high evolvability. We conclude that the parallel opercle evolution is most likely due to selection during adaptation to freshwater habitats, rather than due to biasing effects of opercle genetic architecture.
authors.affiliation: Institute of Neuroscience, University of Oregon, Eugene, Oregon 97403, USA. kimmel@uoneuro.uoregon.edu
authors.forename: Charles B
authors.initials: CB
authors.lastname: Kimmel
authors.forename: William A
authors.initials: WA
authors.lastname: Cresko
authors.forename: Patrick C
authors.initials: PC
authors.lastname: Phillips
authors.forename: Bonnie
authors.initials: B
authors.lastname: Ullmann
authors.forename: Mark
authors.initials: M
authors.lastname: Currey
authors.forename: Frank
authors.initials: F
authors.lastname: von Hippel
authors.forename: Bjarni K
authors.initials: BK
authors.lastname: Kristjánsson
authors.forename: Ofer
authors.initials: O
authors.lastname: Gelmond
authors.forename: Katrina
authors.initials: K
authors.lastname: McGuigan
mesh_terms: D000413:Alaska; D000818:Animals; D005075:Biological Evolution; D017753:Ecosystem; D005618:Fresh Water; D014644:Genetic Variation; D005880:Gills / Q000033:anatomy & histology*; D009922:Oregon; D010641:Phenotype; D023701:Smegmamorpha / Q000033:anatomy & histology* / Q000235:genetics*