High population differentiation and extensive clonality in a rare mallee eucalypt: Eucalyptus curtisii

Abstract

Microsatellite polymorphisms were analysed toassess the extent and pattern of geneticdiversity within and between isolatedpopulations of the rare mallee eucalypt, Eucalyptus curtisii. Twelve populations intotal were sampled throughout the 500 km rangeof the species in South-east Queensland.Results from analysis of 5 loci indicated ahigh degree of clonality within many of thesites, with two populations being comprised ofsingle genets. Estimates of radial growth ratessuggest that these clones may be between 4000and 9000 years old. Low overall levels ofgenetic diversity were recorded for thespecies, H e = 0.54, however a highlysignificant amount of populationdifferentiation was observed, R ST =0.22. There was no evidence of isolation bydistance and although there were morphologicaldifferences between some populations, this wasunrelated to molecular variation. The low level of genetic diversity and highproportion of interpopulation variation agreeswith the findings of other studies onregionally distributed eucalypts. The findingsindicate that previous estimates of theeffective population size of the species arelargely overestimated and that the individualpopulations are sufficiently differentiatedthat they should be treated as separatemanagement units. Further study is recommendedto elucidate the full extent of clonality inthe species and to conduct germination trialson seed collected from clonal populations.