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Latitudinal divergence of common frog (Rana temporaria) life history traits by natural selection: evidence from a comparison of molecular and quantitative genetic data

Authors

  • J. U. Palo,

    1. Ecological Genetics Research Unit, Department of Ecology and Systematics, PO Box 65, FIN-00014 University of Helsinki, Finland,
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  • R. B. O'Hara,

    1. Ecological Genetics Research Unit, Department of Ecology and Systematics, PO Box 65, FIN-00014 University of Helsinki, Finland,
    2. Rolf Nevanlinna Institute, PO Box 4, FIN-00014 University of Helsinki, Finland,
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  • A. T. Laugen,

    1. Department of Population Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18 d, SE-752 36 Uppsala, Sweden,
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  • A. Laurila,

    1. Department of Population Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18 d, SE-752 36 Uppsala, Sweden,
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  • C. R. Primmer,

    1. Department of Ecology and Systematics, PO Box 65, FIN-00014 University of Helsinki, Finland
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  • J. Merilä

    Corresponding author
    1. Ecological Genetics Research Unit, Department of Ecology and Systematics, PO Box 65, FIN-00014 University of Helsinki, Finland,
      Juha Merilä. Fax: + 358-9-191 57694; E-mail: juha.merila@helsinki.fi
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Juha Merilä. Fax: + 358-9-191 57694; E-mail: juha.merila@helsinki.fi

Abstract

The relative roles of natural selection and direct environmental induction, as well as of natural selection and genetic drift, in creating clinal latitudinal variation in quantitative traits have seldom been assessed in vertebrates. To address these issues, we compared molecular and quantitative genetic differentiation between six common frog (Rana temporaria) populations along an approximately 1600 km long latitudinal gradient across Scandinavia. The degree of population differentiation (QST ≈ 0.81) in three heritable quantitative traits (age and size at metamorphosis, growth rate) exceeded that in eight (neutral) microsatellite loci (FST = 0.24). Isolation by distance was clear for both neutral markers and quantitative traits, but considerably stronger for one of the three quantitative traits than for neutral markers. QST estimates obtained using animals subjected to different rearing conditions (temperature and food treatments) revealed some environmental dependency in patterns of population divergence in quantitative traits, but in general, these effects were weak in comparison to overall patterns. Pairwise comparisons of FST and QST estimates across populations and treatments revealed that the degree of quantitative trait differentiation was not generally predictable from knowledge of that in molecular markers. In fact, both positive and negative correlations were observed depending on conditions where the quantitative genetic variability had been measured. All in all, the results suggest a very high degree of genetic subdivision both in neutral marker genes and genes coding quantitative traits across a relatively recently (< 9000 years) colonized environmental gradient. In particular, they give evidence for natural selection being the primary agent behind the observed latitudinal differentiation in quantitative traits.

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