Leaf-stem allometry, hollow stems, and the evolution of caulinary domatia in myrmecophytes

Authors

  • C. Brouat,

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    1. Centre d’Ecologie Fonctionnelle et Evolutive (UPR 9056), CNRS, 1919 route de Mende, 34293 Montpellier Cedex 5, France;
    • Author for correspondence: Carine Brouat Tel: +(33) 4 99 62 33 32 Fax: +(33) 4 99 62 33 45 Email:brouat@ensam.inra.fr

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  • D. McKey

    1. Centre d’Ecologie Fonctionnelle et Evolutive (UPR 9056), CNRS, 1919 route de Mende, 34293 Montpellier Cedex 5, France;
    2. Institut des Sciences de l’Evolution (UMR CNRS 5554), CC 065, Université Montpellier II, Place Eugène Bataillon, 34095 Montpellier Cedex, France
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Summary

  •  Leaf-stem size relationships over ontogeny were studied here in three different lineages of hollow-stemmed myrmecophytes in order to understand how a new stem function affects morphology.
  •  In each of six taxa, the primary cross-sectional area of a terminal internode and the area of the leaf borne by it were measured on plants representing all stages of ontogeny. Cross-sectional areas of both the cavity and the ring of wood were determined.
  •  The leaf-stem relationship over ontogeny was allometric, in contrast to the isometry previously found in solid-stemmed relatives. Stem cross-sectional area was initially larger relative to leaf area than for solid-stemmed species, increasing less than proportionally with increasing leaf size.
  •  Because mechanical stability requires a minimum ratio of t (thickness of the solid ring) to R (external radius of the cylinder), cross-sectional area of the ring of wood must vary with that of the cavity; both contributed to leaf-stem allometry. Relative to leaves, both are initially large and increase more slowly over ontogeny, suggesting that domatia are particularly costly for plants early in development.

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