Molecular genetic diversity and population structure in Eucalyptus pauciflora subsp. pauciflora (Myrtaceae) on the island of Tasmania

Abstract

Genetic diversity and population structure of Tasmanian populations of Eucalyptus pauciflora were assessed using chloroplast and nuclear microsatellite markers. Maternal trees and open-pollinated progeny from 37 populations were sampled across the species’ geographic and altitudinal distribution in Tasmania. The distribution of chloroplast haplotype richness showed a clear geographic structure with suggestion of three major refugia (Storm Bay, Tamar Valley and St Pauls River Valley), two of which are consistent with previously reported glacial refugia. Chloroplast haplotype affinities provided evidence of migration of populations from the north and east towards the south and west of Tasmania. High nuclear microsatellite diversity was observed across the species’ range. Most of this variation was distributed within populations with low but significant FST, suggesting high gene flow among populations that is more pronounced in mature stands. Higher nuclear genetic diversity in newly colonised areas compared with lowland putative refugial regions, and the converse in chloroplast DNA markers, suggest limited seed dispersal into newly colonised regions combined with high pollen flow between different source populations in newly colonised areas. Our results do not support the suggestion that highland populations of E. pauciflora originate from in situ high-altitude refugia, but instead argue they originate from lowland refugia.