Population Genomics in Conservation: Nasturtium gambelii (Gambel’s watercress; Brassicaceae) at Vandenberg Air Force Base

Nila Le; Loraine Washburn, Ph.D.; Naomi Fraga, Ph.D., California Botanic Garden

Nasturtium gambelii (Gambel’s watercress) is a perennial herb in the mustard family that occurs in wetland habitats in California. It is federally listed as Endangered and currently occurs at only one site, reduced from its historic distribution of just ten sites in coastal southern California. Because it is known to hybridize with N. officinale (common watercress), the last remaining population is at risk of disappearing due to genetic swamping. The primary goal of this study was to examine the current genetic integrity of N. gambelii and to provide a framework that will advance key management and recovery actions to ensure its continued persistence in the wild. This study found:
(1) No evidence for genetic hybridization occurring between N. gambelii and N. officinale at Vandenberg Air Force Base (VAFB). We confirm that the VAFB population represents the last known genetically pure N. gambelii individuals in the wild, and that introgression has not occurred since a prior study in 2008;
(2) We identified 12 distinct genotypes for the 14 N. gambelii samples provided from VAFB in 2019;
(3) We estimate 33 total genotypes for each pure and hybrid sample examined in this study.
This information will help guide conservation actions, including identifying samples that can be collected for propagation to advance future restoration, identifying how to best approach its maintenance, and identifying future research needs.