ORIGINAL PAPER Microsatellite diversity and genetic structure of the commercially important tropical tree species Eucalyptus urophylla, endemic to seven islands in eastern Indonesia Kitt G. Payn & William S. Dvorak & Bernard J. H. Janse & Alexander A. Myburg Received: 27 June 2007 / Revised: 12 November 2007 / Accepted: 20 November 2007 # Springer-Verlag 2007 Abstract Eucalyptus urophylla (Timor mountain gum) is an economically important plantation species that occurs naturally in a series of disjunct populations on the volcanic slopes of seven islands in eastern Indonesia. Twelve microsatellite markers were used to investigate the distri- bution of nuclear genetic diversity among 19 geographical- ly defined E. urophylla populations. High levels of gene diversity were observed throughout the geographic range (H E =0.703 to 0.776). The level of genetic differentiation among populations was low (F ST =0.031), but the amount of differentiation increased with geographic distance. A phenogram produced by a neighbor-joining analysis illus- trated that populations clustered according to islands. However, a Bayesian clustering approach revealed a more cryptic population structure comprising two genetically homogeneous groups. Gene flow among the populations is likely responsible for the apparent weak influence of geographic insularity on the genetic diversity and structure of the island species. These findings provide direction for conservation and breeding strategies in E. urophylla. Keywords SSR . Breeding . Conservation . Eucalypt Introduction Eucalyptus urophylla (S.T. Blake) is an important planta- tion species in tropical and subtropical regions of South America, Africa, and Asia (Eldridge et al. 1993). Its natural distribution is limited to a series of disjunct populations located on the volcanic slopes of seven of the Lesser Sunda islands in eastern Indonesia. The largest stands are found on the islands of Timor and Wetar, whereas more scattered stands occur on the islands of Adonara, Alor, Flores, Lomblen (Lembata), and Pantar. Of concern is the apparent depletion in the species' genetic resource, primarily on the latter five islands, as a consequence of land conversion to agriculture (Pepe et al. 2004). Several large-scale seed collections from natural stands of E. urophylla have been carried out in an effort to capture the available genetic diversity and ensure a broad genetic base necessary for effective ex situ conservation and breeding (Martin and Cossalter 1975; Gunn and McDonald 1991; Hodge et al. 2001; Pepe et al. 2004). Proficient management of the genetic resource requires a detailed understanding of the level and structure of genetic variation across the species’ native range. In its natural habitat, E. urophylla is frequently the dominant species of advanced secondary mountain forest (Eldridge et al. 1993). It has the greatest altitudinal range Tree Genetics & Genomes DOI 10.1007/s11295-007-0128-7 DO00128; No of Pages Electronic supplementary material The online version of this article (doi:10.1007/s11295-007-0128-7) contains supplementary material, which is available to authorized users. Communicated by Y. Tsumura K. G. Payn (*) : W. S. Dvorak Camcore, North Carolina State University, P.O. Box 7626, Raleigh, NC 27695, USA e-mail: kitt.payn@fabi.up.ac.za K. G. Payn : B. J. H. Janse Mondi Business Paper South Africa, P.O. Box 31024, Merebank 4059, South Africa K. G. Payn : A. A. Myburg Forest Molecular Genetics Programme, Department of Genetics, Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria 0002, South Africa