Genetic monitoring for effective plant conservation: An example using the threatened Saxifraga hirculus L. in Scotland

Societal Impact Statement Many mountain plants persist in small, isolated patches on the verge of extinction. Observational methods of monitoring these populations, such as recording the number of flowering stems, do not indicate the number of genetically distinct individuals, which is crucial information for conserving small populations. Here, the rate of clonal reproduction and number of genetic individuals were measured in the threatened Saxifraga hirculus in Scotland. These methods showed that population size is a poor proxy for genotype diversity and identified highly diverse small populations that may otherwise have been overlooked. This highlights the necessity of using genetic data to ensure the successful conservation of threatened plants. Summary Habitat fragmentation and loss increase the isolation of plant populations, increasing the occurrence of within population reproduction, and the potential for negative genetic effects, such as inbreeding depression and loss of genetic diversity. We use the European protected Marsh Saxifrage (Saxifraga hirculus) in Scotland as an example for declining perennial plants and the genetic resources they encapsulate. S. hirculus has declined due to agricultural intensification, drainage, industrial afforestation and grazing. The species can spread by seed or vegetatively through the production of rhizomes. Flowering is rare though due to grazing, which limits sexual reproduction and gene flow. An almost complete genetic inventory of Scottish populations was done using 11 microsatellite markers. Furthermore, archived DNA samples were used to document temporal genetic changes. We showed that clonal growth is predominant in some populations and genetic diversity (HS and allelic richness) is relatively high. However, the number of genetically distinct individuals (genets) per population is extremely low (3–34). Archived DNA samples showed that some populations consist of the same few genets with no evidence for turnover. Thus, while clonal growth may have helped the species to persist, there is limited creation of new gene combinations. Our findings highlight that reducing grazing pressure and increasing gene flow will be essential to rescue this species from its evolutionary dead end. We demonstrate the benefits of genetic monitoring for determining census population sizes and thus effective plant management and conservation. This work further sets out a strategy for moving this species towards demographic and genetic sustainability.