Australian Systematic Botany Australian Systematic Botany Society
Taxonomy, biogeography and evolution of plants
RESEARCH ARTICLE

Genetic structuring in the spotted gum complex (genus Corymbia, section Politaria)

Mervyn Shepherd A B , Shabana Kasem A , Gary Ablett A , Joel Ochieng A and Allison Crawford A
+ Author Affiliations
- Author Affiliations

A Centre for Plant Conservation Genetics and Subtropical Forestry Centre, Southern Cross University, PO Box 157, Lismore, NSW 2480, Australia.

B Corresponding author. Email: mervyn.shepherd@scu.edu.au

Australian Systematic Botany 21(1) 15-25 https://doi.org/10.1071/SB07028
Submitted: 27 June 2007  Accepted: 1 November 2007   Published: 3 April 2008

Abstract

Spotted gums (genus Corymbia, section Politaria) occur as a species replacement series along the eastern seaboard of Australia, their distributions marked by regions of disjunction and sympatry. Their taxonomy remains controversial, with species assignment often challenging and reliant on knowledge of geographic origin as well as subtle morphological or leaf-oil variation. In the present paper, we explore a classification for spotted gums, without assuming predefined geographic or taxonomic groups but instead using genetic structure at microsatellite marker loci (n = 9) and a Bayesian model-based clustering approach implemented in Structure software. The C. torelliana outgroup (n = 21; section Cadagaria) formed a well resolved cluster (minimum pairwise Fst = 0.19). Four populations were evident within the spotted gums (n = 93) but structure was weak (pairwise Fst range 0.13–0.05). Geographic distance, topography and distribution disjunction were major determinants of structure, with migration among populations approximating a linear stepping-stone model. Corymbia maculata was resolved as a taxon and had the greatest genetic distance from any other population (minimum pairwise Fst 0.08). Three clusters were evident within the northern taxa but alignment with taxonomic groupings was poor. C. citriodora material from north of a major disjunction in central Queensland formed a Northern population. C. citriodora, C. variegata and C. henryi material south of this disjunction but north of the Border Range, formed a Central population, whereas a Southern population comprised C. variegata and C. henryi from predominately south of the Border Range.


Acknowledgements

This study was supported by ARC grants ‘Eucalypt gene pool management’ LP0455522 awarded to B. Potts and R. Vaillancourt and ‘Wood properties for spotted gum’ LP0348613. The authors are grateful for the assistance and permission of Forests NSW, Queensland DPI&F and Forestry Plantations Queensland for the germplasm used in this study and D. Kleinig for assisting J. Ochieng with collections. The authors also thank T. Bean for identifying herbarium specimens, and D. G. Nikles, D. Lee, C. Nock and C. Harwood for helpful discussions and comments and G. Luker for preparation of Fig. 1.


References


Allendorf FW , Luikart G (2007) Units of conservation. In ‘Conservation and the genetics of populations’. 661 pp. (Blackwell: Malden, MA)

Asante K, Brophy J, Doran J, Goldsack R, Hibbert D, Larmour J (2001) A comparative study of the seedling leaf oils of the spotted gums: species of the Corymbia (Myrtaceae), section Politaria. Australian Journal of Botany 49, 55–56.
CrossRef |

Cornuet JM, Piry S, Lurikart G, Estoup A, Solignac M (1999) New methods employing multilocus genotypes to select or exclude populations as origins of individuals. Genetics 153, 1989–2000.
PubMed |


Dutkowski GW, Potts BM (1999) Geographic patterns of genetic variation in Eucalyptus globulus spp. globulus and a revised racial classification. Australian Journal of Botany 47, 237–263.
CrossRef |

Evanno G, Regnaut S, Goudet J (2005) Detecting the number of clusters of individuals using the software structure: a simulation study. Molecular Ecology 14, 2611–2620.
CrossRef | PubMed |

Excoffier L, Laval G, Schneider S (2005) Arlequin ver. 3.0: an integrated software package for population genetics data analysis. Evolutionary Bioinformatics Online 1, 47–50.

Hill KD, Johnson LAS (1995) Systematic studies in the eucalypts 7. A revision of the bloodwoods, genus Corymbia (Myrtaceae). Telopea 6, 185–504.

Jones M, Stokoe R, Cross M, Scott L, Maguire T, Shepherd M (2001) Isolation of microsatellite loci from spotted gum (Corymbia variegata), and cross-species amplification in Corymbia and Eucalyptus. Molecular Ecology Notes 1, 276–278.
CrossRef |

Kimura M, Weiss GH (1964) The stepping stone model of population structure and the decrease of genetic correlation with distance. Genetics 49, 561–576.
PubMed |


King R (2004) Spatial structure and population genetic variation in a eucalypt species complex. PhD Thesis, Griffith University, Brisbane.

Larmour JS, Whitfeld SJ, Harwood CE, Owen JV (2000) Variation in frost tolerance and seedling morphology of the spotted gums Corymbia maculata, C. variegata, C. henryi and C. citriodora. Australian Journal of Botany 48, 445–453.
CrossRef |

Latch E, Dharmarajan G, Glaubitz J, Rhodes O (2006) Relative performance of Bayesian clustering software for inferring population substructure and individual assignment at low levels of population differentiation. Conservation Genetics 7, 295–302.
CrossRef |

McDonald MW, Bean AR (2000) A new combination in Corymbia section Politaria: C. citriodora var. variegata (Myrtaceae). Austrobaileya 5, 735–736.

McDonald MW, Butcher PA, Bell JC, Larmour JS (2000) Intra- and interspecific allozyme variation in eucalypts from the spotted gum group, Corymbia, section Politaria (Myrtaceae). Australian Systematic Botany 13, 491–507.
CrossRef |

McDonald MW, Butcher PA, Larmour JS, Bell JC (2003) Intra- and interspecific allozyme variation in eucalypts from the spotted gum group, Corymbia, section ‘Politaria’ (Myrtaceae) (vol. 13, p. 491–507, 2000)—correction. Australian Systematic Botany 16, 643–645.
CrossRef |

Moritz C (1994) Defining ‘evolutionary significant units’ for conservation. Trends in Ecology & Evolution 9, 373–375.
CrossRef |

Ochieng JW , Baverstock PR , Henry RJ , Shepherd M (2006) Population panmixia in two sympatric spotted gums (Myrtaceae): implications for association mapping. In ‘14th IPAG Conference’, San Diego, CA. p. P657.

Pritchard JK , Wen W (2004) Documentation for structure software: Version 2. http://pritch.bsd.uchicago.edu/structure.html

Pritchard JK, Stephens M, Donnelly P (2000) Inference of population structure using multilocus genotype data. Genetics 155, 945–959.
PubMed |


Ridley M (2004) Species concepts and intraspecific variation. In ‘Evolution’. 355 pp. (Blackwell: Oxford)

Shepherd M, Kasem S, Lee D, Henry R (2006) Construction of microsatellite linkage maps for Corymbia. Silvae Genetica 55, 228–238.








Export Citation Cited By (24)