Phylogeographical analysis of cpDNA variation in Eucalyptus loxophleba (Myrtaceae)

Abstract

Comparative phylogeography can reveal significant historical events that have had common influences on species with similar distributions. Phylogeographic analyses of eucalypts should provide insight into the influence of historical processes, since eucalypts are a dominant component of the Australian flora. However, use of chloroplast DNA in eucalypts is complicated by sharing of haplotypes among species, which has been attributed to hybridisation and introgression, although these patterns could also be accounted for by incomplete lineage sorting of ancestral polymorphism. Phylogeographic patterns in the cp genome of E. loxophleba Benth., a widespread species throughout southern Western Australia, were investigated by using RFLP analysis. The chloroplast diversity was structured into two geographically distinct lineages and nested clade analysis inferred historical fragmentation as the major influence on the phylogeographic pattern. The divergence between the lineages and their geographic distributions were similar to geographically discrete divergent lineages that have been identified in two other unrelated species from different families in southern Western Australia. Congruence of phylogeographic patterns in the three species provides evidence to support the hypothesis of significant influence of climatic instability during the Pleistocene caused by cyclic contraction and expansion of the mesic and arid zones.