Evolvability and genetic constraint in Dalechampia blossoms: components of variance and measures of evolvability

Authors

  • Thomas F. Hansen,

    1. Department of Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway
    2. Department of Biological Science, Florida State University, Tallahassee, FL 32306, USA
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  • Christophe Pélabon,

    1. Department of Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway
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  • W. Scott Armbruster,

    1. Department of Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway
    2. Institute of Arctic Biology, University of Alaska, Fairbanks, AK 99775, USA
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  • Matthew L. Carlson

    1. Department of Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway
    2. Alaska Natural Heritage Program, Environment and Natural Resources Institute, University of Alaska, Anchorage, AK 99501, USA
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Thomas F. Hansen, Department of Biological Science, Conradi Building, Florida State University, Tallahassee, FL 32306, USA.
Tel.: +1 850 644 4779; fax: +1 850 644 9829;
e-mail: Thomas.Hansen@bio.fsu.edu

Abstract

Abstract Many evolutionary arguments are based on the assumption that quantitative characters are highly evolvable entities that can be rapidly moulded by changing selection pressures. The empirical evaluation of this assumption depends on having an operational measure of evolvability that reflects the ability of a trait to respond to a given external selection pressure. We suggest short-term evolvability be measured as expected proportional response in a trait to a unit strength of directional selection, where strength of selection is defined independently of character variation and in units of the strength of selection on fitness itself. We show that the additive genetic variance scaled by the square of the trait mean, IA, is such a measure. The heritability, h2, does not measure evolvability in this sense. Based on a diallel analysis, we use IA to assess the evolvability of floral characters in a population of the neotropical vine Dalechampia scandens (Euphorbiaceae). Although we are able to demonstrate that there is additive genetic variation in a number of floral traits, we also find that most of the traits are not expected to change by more than a fraction of a percent per generation. We provide evidence that the degree of among-population divergence of traits is related to their predicted evolvabilities, but not to their heritabilities.

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