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

Abstract

Microsatellite polymorphisms were analysed to assess the extent and pattern of genetic diversity within and between isolated populations of the rare mallee eucalypt, Eucalyptus curtisii. Twelve populations in total were sampled throughout the 500 km range of the species in South-east Queensland. Results from analysis of 5 loci indicated a high degree of clonality within many of the sites, with two populations being comprised of single genets. Estimates of radial growth rates suggest that these clones may be between 4000 and 9000 years old. Low overall levels of genetic diversity were recorded for the species, H-e=0.54, however a highly significant amount of population differentiation was observed, R-ST=0.22. There was no evidence of isolation by distance and although there were morphological differences between some populations, this was unrelated to molecular variation. The low level of genetic diversity and high proportion of interpopulation variation agrees with the findings of other studies on regionally distributed eucalypts. The findings indicate that previous estimates of the effective population size of the species are largely overestimated and that the individual populations are sufficiently differentiated that they should be treated as separate management units. Further study is recommended to elucidate the full extent of clonality in the species and to conduct germination trials on seed collected from clonal populations.