Breeding system and population genetics of the vulnerable plant Dillwynia tenuifolia (Fabaceae)

Dillwynia tenuifolia Sieber ex DC. is a vulnerable species endemic to the Sydney region in Australia. This investigation focused on the breeding system and genetic structuring of the species in locations encompassing its entire geographical range. A field pollination experiment showed that D. tenuifolia produced fruit from both self- and cross-pollination events, and thus has a facultative breeding system. Fruiting success from self-pollination was approximately half that observed from cross-pollination. The genetic structure of D. tenuifolia populations was investigated by using allozyme electrophoresis. A survey of 16 loci revealed a high level of genetic variation with approximately two-thirds of the loci being polymorphic and a mean of 1.84 alleles per loci. The genotype frequencies deviated from the Hardy-Weinberg equilibrium, with the observed level of heterozygosity significantly less than expected. The inbreeding coefficient was 0.31. There was very little divergence between populations (F ST = 0.04) but the fixation indices were high within populations. Spatial autocorrelation, using Moran's I, showed that neighbouring plants were closely related (I>0.4). The genetic neighbourhood and effective population size in the species were estimated at one location as 1.1 ha and 10 4 plants, respectively.