title: Variation in Lateral Plate Quality in Threespine Stickleback from Fresh, Brackish and Marine Water: A Micro-Computed Tomography Study.
abstract: BACKGROUND
  It is important to understand the drivers leading to adaptive phenotypic diversity within and among species. The threespine stickleback (Gasterosteus aculeatus) has become a model system for investigating the genetic and phenotypic responses during repeated colonization of fresh waters from the original marine habitat. During the freshwater colonization process there has been a recurrent and parallel reduction in the number of lateral bone plates, making it a suitable system for studying adaptability and parallel evolution.
  
  
  OBJECTIVE
  The aim of this study was to investigate an alternative evolutionary path of lateral plate reduction, where lateral plates are reduced in size rather than number.
  
  
  METHODS
  A total of 72 threespine stickleback individuals from freshwater (n = 54), brackish water (n = 27) and marine water (n = 9) were analysed using microcomputed tomography (μCT) to determine variation in size, thickness and structure of the lateral plates. Furthermore, whole-body bone volume, and bone volume, bone surface and porosity of lateral plate number 4 were quantified in all specimens from each environment.
  
  
  RESULTS
  The results showed a significant difference in plate size (area and volume) among populations, where threespine stickleback from polymorphic freshwater and brackish water populations displayed lateral plates reduced in size (area and volume) compared to marine stickleback.
  
  
  CONCLUSIONS
  Reduction of lateral plates in threespine stickleback in fresh and brackish water occurs by both plate loss and reduction in plate size (area and volume).
authors.affiliation: Department of Biosciences, Centre for Ecological and Evolutionary Synthesis (CEES), University of Oslo, PO Box 1066, Blindern, Oslo, N-0316, Norway.|Department of Biomaterials, Faculty of Dentistry, University of Oslo, PO Box 1109, Blindern, Oslo, N-0317, Norway.
authors.forename: Elisabeth
authors.identifier: http://orcid.org/0000-0003-4548-9180
authors.initials: E
authors.lastname: Wiig
authors.affiliation: Department of Biomaterials, Faculty of Dentistry, University of Oslo, PO Box 1109, Blindern, Oslo, N-0317, Norway.
authors.forename: Janne E
authors.initials: JE
authors.lastname: Reseland
authors.affiliation: Department of Biosciences, Centre for Ecological and Evolutionary Synthesis (CEES), University of Oslo, PO Box 1066, Blindern, Oslo, N-0316, Norway.|Department of Forestry and Wildlife Management, Hedmark University College, Campus Evenstad, Elverum, NO-2418, Norway.
authors.forename: Kjartan
authors.initials: K
authors.lastname: Østbye
authors.affiliation: Department of Biomaterials, Faculty of Dentistry, University of Oslo, PO Box 1109, Blindern, Oslo, N-0317, Norway.
authors.forename: Håvard J
authors.initials: HJ
authors.lastname: Haugen
authors.affiliation: Department of Biosciences, Centre for Ecological and Evolutionary Synthesis (CEES), University of Oslo, PO Box 1066, Blindern, Oslo, N-0316, Norway.
authors.forename: Leif A
authors.initials: LA
authors.lastname: Vøllestad
mesh_terms: D000220:Adaptation, Biological; D000818:Animals; D005618:Fresh Water / Q000032:analysis*; D009929:Organ Size; D012623:Seawater / Q000032:analysis*; D012641:Selection, Genetic; D023701:Smegmamorpha / Q000033:anatomy & histology*; D055114:X-Ray Microtomography