Multiple evolutionary processes drive the patterns of genetic differentiation in a forest tree species complex

Authors

  • Rebecca C. Jones,

    Corresponding author
    1. CRC for Forestry, Hobart, Tasmania, Australia
    • School of Plant Science, University of Tasmania, Hobart, Tasmania, Australia
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  • Dorothy A. Steane,

    1. School of Plant Science, University of Tasmania, Hobart, Tasmania, Australia
    2. CRC for Forestry, Hobart, Tasmania, Australia
    3. Faculty of Science, Health, Education and Engineering, University of the Sunshine Coast, Sippy Downs, Queensland, Australia
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  • Martyn Lavery,

    1. Arianda Pty Ltd, Williamstown, Victoria, Australia
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  • René E. Vaillancourt,

    1. School of Plant Science, University of Tasmania, Hobart, Tasmania, Australia
    2. CRC for Forestry, Hobart, Tasmania, Australia
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  • Brad M. Potts

    1. School of Plant Science, University of Tasmania, Hobart, Tasmania, Australia
    2. CRC for Forestry, Hobart, Tasmania, Australia
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Correspondence

Rebecca C. Jones, School of Plant Science, University of Tasmania, Private Bag 55, Hobart, Tasmania 7001, Australia. Tel: +613 6226 2736; Fax: +613 6226 2698; E-mail Rebecca.Jones@utas.edu.au

Abstract

Forest trees frequently form species complexes, complicating taxonomic classification and gene pool management. This is certainly the case in Eucalyptus, and well exemplified by the Eucalyptus globulus complex. This ecologically and economically significant complex comprises four taxa (sspp. bicostata, globulus, maidenii, pseudoglobulus) that are geographically and morphologically distinct, but linked by extensive “intergrade” populations. To resolve their genetic affinities, nine microsatellites were used to genotype 1200 trees from throughout the natural range of the complex in Australia, representing 33 morphological core and intergrade populations. There was significant spatial genetic structure (FST = 0.10), but variation was continuous. High genetic diversity in southern ssp. maidenii indicates that this region is the center of origin. Genetic diversity decreases and population differentiation increases with distance from this area, suggesting that drift is a major evolutionary process. Many of the intergrade populations, along with other populations morphologically classified as ssp. pseudoglobulus or ssp. globulus, belong to a “cryptic genetic entity” that is genetically and geographically intermediate between core ssp. bicostata, ssp. maidenii, and ssp. globulus. Geography, rather than morphology, therefore, is the best predictor of overall genetic affinities within the complex and should be used to classify germplasm into management units for conservation and breeding purposes.

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