Geographic Patterns of Genetic Diversity in Karri (Eucalyptus diversicolor F. Muell.)

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Abstract
Karri (Eucalyptus diversicolor) is a large dominant timber tree which occupies a limited area of high rainfall in south-western Australia. The level and geographic distribution of genetic vadation were studied at 16 polymorphic allozyme loci. Geographical trends were observed only at the Adh-1 locus with the fastest allele restricted to the westerly end of the species distribution. The mean number of alleles per locus per population (A = 1.60) and the expected panmictic heterozygosity (He = 0.15) are generally low when compared with most other eucalypts. Much of the genetic variation in karri occurs within populations (Hs = 0.270) rather than between (Gst = 0.092), However, certain outlying populations exhibit noticeable levels of genetic divergence from the main karri forest, whereas no significant differentlation was found between populations from different river catchments within the main forest. Strategies for the conservation of genetic resources of karri are discussed in the light of these findings. The lack of genetic differentiation between the southern coastal outliers and the main forest indicates more recent separation than outlying populations to the north-east and west which probably separated from the main distribution as aridity increased from about 5000 B.P. Differences in the average fixation index F between populations, although not always significant, were sufficient to suggest that there could be real differences in the level of outcrossing between some populations.