Genetic Diversity and the Conservation of Eucalyptus crucis Maiden

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Abstract
E. crucis Maiden occurs as small, isolated populations confined to granite outcrops in south-western Australia. The level and distribution of genetic diversity at 11 allozyme loci in 10 populations were estimated. Ten loci were polymorphic. However, many alleles were fixed in populations and occurred at low frequencies in others. The mean expected panmictic heterozygosity for populations was low when compared with tree species in general but similar to other tree species occurring in small, isolated populations. The level of population differentiation was high, as expected for small, isolated populations undergoing genetic fixation through genetic drift. The majority of the differentiation was attributable to between-population rather than between-subspecies differentiation. Analyses of allozyme data suggest that the mating system of E. crucis may be adapted to maintain diversity within populations by selection favouring heterozygous, presumably outcrossed progeny. The optimal strategy for the conservation of the genetic resources of E. crucis and other eucalypts with similar distribution patterns is considered in the light of this and previous studies.