High genetic diversity with moderate differentiation in Juniperus excelsa from Lebanon and the eastern Mediterranean region

BACKGROUND AND AIMS Juniperus excelsa is an important woody species in the high mountain ecosystems of the eastern Mediterranean Basin where it constitutes the only coniferous species found at the tree line. The genetic diversity within and among J. excelsa populations of the eastern Mediterranean Basin is studied in the light of their historical fragmentation. METHODOLOGY Nuclear microsatellites originally developed for Juniperus communis and J. przewalskii were tested on 320 individuals from 12 different populations originating from Lebanon, Turkey, Cyprus, Greece and the Ukraine. PRINCIPAL RESULTS Among the 31 nuclear microsatellite primers tested, only three produced specific amplification products, with orthology confirmed by sequence analysis. They were then used for genetic diversity studies. The mean number of alleles and the expected heterozygosity means were N(a)=8.78 and H(e)=0.76, respectively. The fixation index showed a significant deviation from Hardy-Weinberg equilibrium and an excess of homozygotes (F(IS)=0.27-0.56). A moderate level of genetic differentiation was observed among the populations (F(ST)=0.075, P<0.001). The most differentiated populations corresponded to old vestigial stands found at the tree line (>2000 m) in Lebanon. These populations were differentiated from the other populations that are grouped into three sub-clusters. CONCLUSIONS High levels of genetic diversity were observed at species and population levels. The high level of differentiation in the high-mountain Lebanese populations reflects a long period of isolation or possibly a different origin. The admixture observed in other populations from Lebanon suggests a more recent separation from the Turkish-southeastern European populations.