Genotypes and phenotypes: reconstructing the phylogeographic evolution of the Tasmanian blue gum, Eucalyptus globulus (Myrtaceae)

The Tasmanian blue gum, Eucalyptus globulus, is native to Tasmania, the Bass Strait Islands, and Victoria on the Australian mainland. Phenotypic differences between many populations are marked, and a racial classification for the species, based on quantitative traits, is used widely by breeders for genetic improvement. We used nuclear microsatellite markers and chloroplast DNA to examine genetic relationships between races and ecotypes of E. globulus. Comparisons of quantitative and molecular data show that phenotypes are influenced by directional selection, resulting in phenotypic convergence in geographically disjunct populations, as well as phenotypic divergence in parapatric populations. Hence, selectively neutral molecular markers such as microsatellites are useful for differentiating populations of E. globulus on the basis of geographic region, but may not provide information about the distribution of adaptively important traits in localised environment s within those regions. Data from chloroplast DNA, nuclear microsatellite markers and quantitative traits combine to provide a detailed picture of the phylogeographic evolution of the Tasmanian blue gum