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 AA 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.
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