GENE FLOW AND CONSERVATION GENOMICS OF DUDLEYA ABRAMSII SSP. SETCHELLII, AN ENDANGERED SUCCULENT IN SANTA CLARA COUNTY

Understanding how gene flow shapes the distribution of genetic variation is essential for the conservation of rare and geographically restricted species. We investigated genomic structure, clonality, and mechanisms of gene flow in the federally endangered, serpentine endemic Dudleya abramsii ssp. setchellii (Jeps.) Moran using low-coverage whole-genome resequencing of 52 individuals representing 13 populations of D. a. ssp. setchellii, four populations of the geographically adjacent D. cymosa (Lem.) Britton & Rose, and two other subspecies of D. abramsii from San Luis Obispo County. Genome-wide comparisons were combined with analyses of clonality, isolation by distance, principal component analysis, phylogenetic reconstruction, pollinator observations, and a controlled seed dispersal experiment. Strong isolation by distance was detected both within a focal population and among populations across the species' range, indicating that genetic differentiation increases predictably with geographic separation. Clonal reproduction was present, but restricted to individuals separated by only a few centimeters, contributing little to broader spatial genetic structure. Genomic analyses recovered D. a. ssp. setchellii as a distinct lineage exhibiting geographic subdivision within the species and identified a putative hybrid with D. cymosa. Field observations identified bumblebees as the dominant floral visitors, suggesting the potential for pollen-mediated gene flow, whereas a controlled seed dispersal experiment showed that most seeds traveled only a few meters under the artifically optimal experimental wind conditions. Together, these results suggest that limited seed dispersal may contribute to the pronounced spatial genetic structure observed in this serpentine endemic, although the relative contributions of pollen-mediated gene flow, geographic isolation, and genetic drift remain unresolved. These findings provide a genomic framework for conservation and identify geographically structured populations (east vs. west of Coyote Valley) as important units for long-term management.