Clonality and inbreeding amplifies genetic isolation and mate limitation in a rare montane woody plant (Persoonia hindii; Proteaceae)

Small populations have genetic attributes that make them prone to extinction, including low effective population size (Ne), increased levels of inbreeding, and negative impacts from genetic drift. Some small populations are also clonal with low levels of genetic diversity, restricted seed dispersal, and high levels of genetic structure. Together, these attributes make species with small, isolated, clonal populations unlikely to persist under environmental change. We investigated an endangered woody plant species (Persoonia hindii) in eastern Australia to answer key questions about genetic differentiation, migration rates, population sizes, size of clones, mating system and Ne. We identified 587 single nucleotide polymorphisms. Of the 88 individual stems collected from 15 sites across the entire distribution of P. hindii, we identified 30 multi-locus genotypes (MLG). Additional fine-scale genotyping of two sites (49 and 47 stems) detected a dominant genet within each site occupying a minimum area of 20 m2. Global population differentiation was high (FST 0.22) with very low migration rates (0.048 - 0.064). We identified some population structure with variable site pairwise differentiation (0.015 - 0.32) with no detectable spatial autocorrelation. Species wide inbreeding coefficient was 0.42 (FIT), supporting the direct estimate of 82% selfing. Estimated Ne was extremely small (15), indicating that genetic drift may be reducing genetic diversity and increasing genetic load through fixation of deleterious alleles. Clonality and inbreeding combined with negligible gene flow suggests limited adaptive capacity to respond to climate challenges. Genetic rescue, through assisted gene migration and experimental translocations, would enhance the persistence of natural populations.