Genomic diversity of the narrow endemic and endangered legume Astragalus tricarinatus

Link To Share This Poster: https://cdmcd.co/XGgLnL
Live Discussion Link: https://cdmcd.co/w3QnRR

Lynn Sweet, Center for Conservation Biology, University of California, Riverside, CA, Lorena Torres-Martinez, University of California, Riverside, Riverside, CA, Naomi Fraga, California Botanic Garden, Claremont, CA, Tasha La Doux, Joshua Tree National Park, National Park Service, Twentynine Palms, CA, Scott Heacox and Melanie Davis, Center for Conservation Biology, University of California, Riverside, Palm Desert, CA, Joel Sachs, Department of Biology, University of California Riverside, Riverside, CA

Background/Question/Methods
Plant species with narrow geographic ranges are inherently rare and face increasing threats of endangerment due to anthropogenic landscape modifications and shifts in climate. The survival of these species depends on the maintenance of genetic variation within populations and the promotion of gene flow across the species range. We evaluated patterns of genetic variation across the narrow range of the rare and endemic California legume Astragalus tricarinatus (triple-ribbed milkvetch). In 1998, A. tricarinatus was listed as endangered due to direct threats to the <100 known individuals occurring along ephemeral sandy benches in canyon bottoms in the San Bernardino (SBM) and Little San Bernardino Mountains (LSB). Since its listing, we have learned that such occurrences are waif populations found downslope from larger populations; and the role of the waifs in maintaining gene flow has been of great concern. Through genotyping-by-sequencing (GBS) of leaf tissue from 132 individuals collected within the Mojave and Colorado Deserts in the SBM, LSB and Santa Rosa Mountains (SRM), we assessed i) whether populations of this short-lived perennial herb are genetically connected, particularly between the disjunct SRM and SBM, and ii) whether waif individuals are promoting gene flow among populations found on the canyon slopes.
Results/Conclusions
Genetic variation across the species range was relatively high (Õ=0.17) with respect to other rare species, and mild divergence among sampling locations was observed (FST= 0.08). The disjunct SRM population had the lowest genetic variation, the highest divergence with respect to other locations (FST=0.30-0.20) but is genetically similar to specific populations in SBM, suggesting that a long-distance dispersal event might have founded this population. Furthermore, the levels and patterns of admixture and relatedness found among waif and canyon populations in the SBM and LSB areas indicate high genetic connectivity that is likely due to waif individuals. Our findings are the first genetic description of this dynamic system and indicate that the conservation of waif populations will be vital for the species survival.