Origins of a morphological cline between Eucalyptus melanophloia and Eucalyptus whitei
James E. Holman A , Jane M. Hughes A and Roderick J. Fensham B C D
+ Author Affiliations
- Author Affiliations
A Griffith School of Environment, Griffith University, Nathan, Brisbane, Qld 4111, Australia.
B Queensland Herbarium, Department of Environment and Resource Management, Brisbane Botanic Gardens, Mt Coot-tha Road, Toowong, Qld 4066, Australia.
C The Ecology Centre, School of Biological Sciences, University of Queensland, St Lucia, Qld 4072, Australia.
D Corresponding author. Email: rod.fensham@derm.qld.gov.au
Australian Journal of Botany 59(3) 244-252 https://doi.org/10.1071/BT10209
Submitted: 19 August 2010 Accepted: 11 March 2011 Published: 9 May 2011
Abstract
Most theories to explain the origin and maintenance of clines in Eucalyptus are based on a morphological classification system. The true relationships between putative species along clines require detailed investigation of phylogenetic relationships. A cline between Eucalyptus melanophloia and E. whitei was examined using morphological and molecular analyses to determine whether genetic structuring in nuclear and chloroplast DNA along the cline could be explained by secondary contact between independent evolutionary lineages, or whether the cline represents a single species that has undergone primary differentiation. Morphological analysis showed phenotypic variation distributed continuously across the cline and that seedlings bred true to parental type. Microsatellite analysis indicated that there was little genetic structuring across the cline, and low levels of population differentiation. This result was further reinforced by analysis of the cpDNA. The phylogeographic distribution of cpDNA haplotypes is likely to have resulted from restricted seed-mediated gene flow with isolation by distance. A cogent explanation for the cline is that it has arisen by selection on leaf types promoted by a gradient in precipitation with the short-broad, subsessile leaves of E. melanophloia favoured under higher rainfall and the long, narrow, petiolate leaves of E. whitei favoured in arid environments.
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