Population and phylogenetic analysis of the cinnamoyl coA reductase gene in Eucalyptus globulus (Myrtaceae)

Abstract

Low-copy number nuclear genes are currently emerging as new markers for phylogenetic and phylogeographic analysis. This study used the single-copy gene for cinnamoyl coA reductase (CCR) to gain insights into the evolutionary history of the forest tree Eucalyptus globulus Labill. (subgenus Symphyomyrtus, section Maidenaria). A population analysis based on CCR restriction fragments from E. globulus was combined with a phylogenetic analysis of 1.5 kb of CCR sequence from the major haplotypes. Two highly divergent CCR lineages were found in E. globulus. One lineage was prominent throughout the species’ range and was identified in 16 other Maidenaria species by restriction analysis. The second lineage, which was prominent in the northern part of the species’ range, was found only in species of the E. globulus complex and surprisingly showed homology to CCR from Eucalyptus saligna Smith (subgenus Symphyomyrtus, section Latoangulatae). This finding may reflect either incomplete lineage sorting in CCR, or reticulate evolution. No statistically significant phylogeographic structure (geographic clustering of closely related haplotypes) was detected. However, patterns of CCR haplotypic diversity were congruent with patterns of chloroplast DNA diversity in several respects, and divided the range of E. globulus into four regions, supporting (1) former gene flow between King Island and western Tasmania, (2) gene flow between northern Tasmania, the Furneaux Group and Victoria, and (3) a genetic disjunction between north-eastern and south-eastern Tasmania, consistent with separate histories for these two regions.