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Life-history differentiation and the maintenance of monoecy and dioecy in Sagittaria latifolia (Alismataceae).

Abstract

The existence of monoecious and dioecious populations within plant species is rare. This limits opportunities to investigate the ecological mechanisms responsible for the evolution and maintenance of these contrasting sexual systems. In Sagittaria latifolia, an aquatic flowering plant, monoecious and dioecious populations exist in close geographic proximity but occupy distinct wetland habitats differing in the relative importance of disturbance and competition, respectively. Life-history theory predicts contrasting evolutionary responses to these environmental conditions. We propose that the maintenance of monoecy and dioecy in S. latifolia is governed by ecological selection of divergent life-history strategies in contrasting habitats. Here we evaluate this hypothesis by comparing components of growth and reproduction between monoecious and dioecious populations under four conditions: natural populations, a uniform glasshouse environment, a common garden in which monoecious and dioecious populations and their F1 progeny were compared, and a transplant experiment using shaded and unshaded plots in a freshwater marsh. Plants from dioecious populations were larger in size and produced heavier corms in comparison with monoecious populations. Monoecious populations flowered earlier and produced more flowers, clonal ramets, and corms than dioecious populations. The life-history differences between the sexual systems were shown to have a quantitative genetic basis, with F1 progeny generally exhibiting intermediate trait values. Survival was highest for each sexual system in field plots that most closely resembled the habitats in which monoecious (unshaded) and dioecious (shaded) populations grow. These results demonstrate that monoecious and dioecious populations exhibit contrasting patterns of investment in traits involved with growth and reproduction. Selection for divergent life histories between monoecious and dioecious populations of S. latifolia appears to be the principal mechanism maintaining the integrity of the two sexual systems in areas of geographic overlap.

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  • Authors+Show Affiliations

    ,

    Department of Botany, University of Toronto, 25 Willcocks Street, Toronto, Ontario, Canada M5S 3B2.

    Source

    MeSH

    Adaptation, Physiological
    Biological Evolution
    Crosses, Genetic
    Environment
    Fresh Water
    Ontario
    Principal Component Analysis
    Reproduction
    Sagittaria
    Selection, Genetic

    Pub Type(s)

    Comparative Study
    Journal Article
    Research Support, Non-U.S. Gov't

    Language

    eng

    PubMed ID

    14575320