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Molecular and morphological evidence of natural interspecific hybridization between the uncommon Eucalyptus aggregata and the widespread E. rubida and E. viminalis

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Abstract

Human activities can promote increased hybridization in the genus Eucalyptus with potentially detrimental consequences for the persistence of rare species. However, many hybrid combinations have not been investigated with combined use of genetic markers and morphology. We assessed the efficiency of the STRUCTURE program and morphological intermediacy for identifying hybrids between the uncommon tree, Eucalyptus aggregata, which putatively hybridizes with the common congeners, E. rubida and E. viminalis in south-eastern Australia. We sampled 1,005 seedlings across 27 populations, all seedlings were genotyped at 6 allozyme loci and scored for 22 stem and leaf characters. Both marker sets confirmed that E. aggregata is hybridizing with both E. rubida and E. viminalis. Allozymes revealed hybrids from E. aggregata trees in 88% of populations and hybrids comprised 7.3% of all seedlings. Both genetics and morphology indicated that ~50% were likely to be F1 hybrids, and both simulations and morphological characteristics indicated that the remainder were mostly backcrosses. Morphological analysis correctly distinguished 71% of F1 hybrids from parentals and was least accurate when dealing with potential backcrosses (50% success). Hence, techniques using genetic data (no prior information) and the assessment of appropriate admixture thresholds through simulations provided the most accurate estimates of hybrid frequency. In this study, potential introgression and the high frequency of hybrids in small populations (~30%), suggests that hybridization should be considered in the management and conservation of E. aggregata.

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Acknowledgements

We thank Andrew Slee and John Connors for assistance with Eucalyptus classification. We also thank Linda Broadhurst, Anthony Whelan, Tony Brown, Leanne Cox, Robert Godfree, Liz Gregory, and Melinda Pickup for assistance. This work was conducted while (D.L.F.) was receiving a University of Wollongong Post-graduate Research Award and ‘top-up’ scholarship from CSIRO Plant Industry.

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Authors and Affiliations

  1. Department of Ecology and Evolutionary Biology, 25 Willcocks street, Toronto, ON, Canada, M5S 3B2

    David L. Field

  2. School of Biological Sciences, Institute for Conservation Biology, University of Wollongong, Wollongong, NSW, 2522, Australia

    David J. Ayre & Rob J. Whelan

  3. CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia

    Andrew G. Young

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  1. David L. Field
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Correspondence to David L. Field.

Appendix

Appendix

Table A1 Description of morphological traits scored on pure-bred and hybrid Eucalyptus seedlings (n = 1,005) and tests for differentiation between genealogical classes (d.f. = 6) and population (d.f. = 27)
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Field, D.L., Ayre, D.J., Whelan, R.J. et al. Molecular and morphological evidence of natural interspecific hybridization between the uncommon Eucalyptus aggregata and the widespread E. rubida and E. viminalis . Conserv Genet 10, 881–896 (2009). https://doi.org/10.1007/s10592-008-9649-3

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