On the edge: Conservation genomics of the critically endangered dwarf mountain pine Pherosphaera fitzgeraldii

Pherosphaera fitzgeraldii, the Dwarf Mountain Pine, is a critically endangered conifer restricted to cliff ledges within the spray zones of waterfalls in the Greater Blue Mountains Area of New South Wales, Australia. This species is under threat from pollution, invasive weeds, and limited recruitment, which are contributing to its declining population. Using a comprehensive conservation genomic approach, we assessed the population health of P. fitzgeraldii and developed strategic recommendations for its management. Genomic analysis of P. fitzgeraldii revealed the presence of two distinct genetic groups despite the limited distribution of the species. This genetic structure aligns with prevailing wind currents, indicating potential restrictions to pollen or seed exchange between subpopulations. Furthermore, limited gene flow was observed even among nearby subpopulations, emphasizing the risk of increased genetic differentiation due to ongoing isolation. Clonality is widespread in some subpopulations, and all subpopulations displayed signs of inbreeding and genetic depletion despite subdioecy, indicative of historical constraints on gene flow and small population sizes. We offer genomic-based recommendations for prioritizing conservation sites, enhancing genetic diversity in ex situ collections, and guiding future management. Further studies to uncover the sex determination mechanism of P. fitzgeraldii could help maintain balanced sex ratios in ex situ collections and support future genetic rescue efforts. This study underscores the value of genomics in informing protection and recovery of unique threatened species.