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 10⁴ plants, respectively.