Population Genomic Assessment of Dudleya brevifolia for in situ Conservation Management.

Background and aims: San Diego County, United States, is a botanically biodiverse region with many rare, endangered, and endemic plants found across a wide range of habitats. Dudleya brevifolia is a small deciduous succulent that is endemic to the southwest coastal bluffs of San Diego. It is listed as critically imperiled globally (G1), with only five known occurrences, all located within a ten-kilometer radius.

Methods: To better inform conservation management strategies, we conducted molecular population genetic assessments using double digest restriction site-associated DNA sequencing data. We studied genetic diversity, inbreeding, population differentiation, genetic structure, and demographic history of seven D. brevifolia collection sites.

Key results: Genetic diversity within sites was found to be moderate, while inbreeding was relatively low (HO = 0.22- 0.25; FIS < 0.10), genetic differentiation was moderate to high (FST = 0.05- 0.27), and patterns of genetic structure and admixture supported genetic isolation with limited gene flow between three genetic clusters identified as management units. Demographic analyses suggested historical and contemporary gene flow, as well as recent population decline.

Conclusions: Population-level genetic assessments support the management of D. brevifolia through continued monitoring of sites and active augmentation of small occurrences with either seeds or new individuals collected from wild or nursery-propagated plants that share a similar genetic ancestry.