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Adaptation at specific loci. VII. Natural selection, dispersal and the diversity of molecular–functional variation patterns among butterfly species complexes (Colias: Lepidoptera, Pieridae)

Authors

  • W. B. Watt,

    Corresponding author
    1. Rocky Mountain Biological Laboratory, Crested Butte, Colorado, USA;
    2. Center for Evolutionary Studies, Department of Biological Sciences, 371 Serra Mall, Stanford University, Stanford, CA 94305-5020 USA
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  • C. W. Wheat,

    1. Rocky Mountain Biological Laboratory, Crested Butte, Colorado, USA;
    2. Center for Evolutionary Studies, Department of Biological Sciences, 371 Serra Mall, Stanford University, Stanford, CA 94305-5020 USA
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    • Present address: Abteilung Genetik, Max-Planck-Institut für chemische Oekologie, Jena, Germany.

  • E. H. Meyer,

    1. Rocky Mountain Biological Laboratory, Crested Butte, Colorado, USA;
    2. Center for Evolutionary Studies, Department of Biological Sciences, 371 Serra Mall, Stanford University, Stanford, CA 94305-5020 USA
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    • §

      Present address: Program in Immunology, Stanford University, Stanford, USA.

  • J.-F. Martin

    1. Rocky Mountain Biological Laboratory, Crested Butte, Colorado, USA;
    2. Center for Evolutionary Studies, Department of Biological Sciences, 371 Serra Mall, Stanford University, Stanford, CA 94305-5020 USA
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    • Present address: Centre de Biologie et de Gestion des Populations, Campus International de Baillarguet, Montferrier/Lez, France.


W. B. Watt. Present address: Center for Evolutionary Studies, Department of Biological Sciences, 371 Serra Mall, Stanford University, Stanford, CA 94305-5020, USA. E-mail: wbwatt@stanford.edu

Abstract

Natural genetic variants at the phosphoglucose isomerase, PGI, gene differ in spatial patterning of their polymorphism among species complexes of Colias butterflies in North America. In both lowland and alpine complexes, molecular–functional properties of the polymorphic genotypes can be used to predict genotype-specific adult flight performances and resulting large genotypic differences in adult fitness components. In the lowland species complex, there is striking uniformity of PGI polymorph frequencies at a number of sites across the American West; this fits with earlier findings of strong, similar differences in fitness components over this range. In an alpine complex, Colias meadii shows similar uniformity of PGI frequencies within habitat types, either montane steppe or alpine tundra, over several hundred kilometres in the absence of dispersal. At the same time, large shifts (10–20%) in frequency of the most common alleles occur between steppe and tundra populations, whether these are isolated or, as in some cases, are in contact and exchange many dispersing adults each generation. Data on male mating success of common C. meadii PGI genotypes in steppe and tundra show heterozygote advantage in both habitat types, with shifts in relative homozygote disadvantage between habitats which are consistent with observed frequency differences. Nonadaptive explanations for this situation are rejected, and alternative, thermal-ecology-based adaptive hypotheses are proposed for later experimental test. These findings show that strong local selection may dominate dispersal as an evolutionary agent, whether or not dispersal is present, and that selection may often be the major force promoting ‘cohesion’ of species over long distances. This case offers new opportunities for integrating studies of molecular structure and function with ecological aspects of natural selection in the wild, both within and among species.

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