Parallel evolution of dwarf ecotypes in the forest tree Eucalyptus globulus

Authors

  • Susan A. Foster,

    1. School of Plant Science and Cooperative Research Centre for Forestry, University of Tasmania, Private Bag 55, Hobart, Tasmania 7001, Australia
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  • Gay E. McKinnon,

    1. School of Plant Science and Cooperative Research Centre for Forestry, University of Tasmania, Private Bag 55, Hobart, Tasmania 7001, Australia
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  • Dorothy A. Steane,

    1. School of Plant Science and Cooperative Research Centre for Forestry, University of Tasmania, Private Bag 55, Hobart, Tasmania 7001, Australia
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  • Brad M. Potts,

    1. School of Plant Science and Cooperative Research Centre for Forestry, University of Tasmania, Private Bag 55, Hobart, Tasmania 7001, Australia
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  • René E. Vaillancourt

    1. School of Plant Science and Cooperative Research Centre for Forestry, University of Tasmania, Private Bag 55, Hobart, Tasmania 7001, Australia
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Author for correspondence: René Vaillancourt Tel: +61 03 62267137 Fax: +61 03 62262698 Email: R.Vaillancourt@utas.edu.au

Summary

  • • Three small populations of a dwarf ecotype of the forest tree Eucalyptus globulus are found on exposed granite headlands in south-eastern Australia. These populations are separated by at least 100 km.
  • • Here, we used 12 nuclear microsatellites and a chloroplast DNA marker to investigate the genetic affinities of the dwarf populations to one another and to their nearest populations of tall E. globulus. Cape Tourville was studied in greater detail to assess the processes enabling the maintenance of distinct ecotypes in close geographical proximity.
  • • The three dwarf populations were not related to one another and were more closely related to adjacent tall trees than to one another. At Cape Tourville the dwarf and tall ecotypes were significantly differentiated in microsatellites and in chloroplast DNA. The dwarf and tall populations differed in flowering time and no evidence of pollen dispersal from the more extensive tall to the dwarf population was found.
  • • The three dwarf populations have evolved in parallel from the local tall ecotypes. This study shows that small marginal populations of eucalypts are capable of developing reproductive isolation from nearby larger populations through differences in flowering time and/or minor spatial separation, making parapatric speciation possible.

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