New genetic markers for identifying heritage plant species from the Aquitaine coast - ISO SGDC

The role of genetic diversity in maintaining species diversity and ecosystem functioning is now widely recognised. In the face of environmental change, this diversity contributes significantly to the resilience of ecosystems and the adaptive capacity of species. Integrating genetic diversity within species is therefore essential in order to implement management and conservation measures. The lakes and ponds of the Aquitaine coastline, ecosystems that are unique on a national and European scale, are home to significant plant biodiversity that is now seriously threatened.

While the taxonomic diversity of these communities is well known, knowledge of their genetic diversity is currently non-existent. However, improving this knowledge seems essential for better management of these ecosystems, particularly for their heritage species.

Joint analysis of the relationships between species genetic diversity within a community and taxonomic diversity of communities (species–genetic diversity correlations) provides a better understanding of how communities function and the processes responsible for the assembly of their species. Studying these two levels of diversity also makes it possible to assess whether the taxonomic diversity commonly used in conservation practices adequately takes into account the evolutionary processes revealed by genetic diversity.

Approaches

To this end, nine species belonging to the “isoetid” communities of five water bodies on the Aquitaine coast were sampled: Lobelia dortmanna, Littorella uniflora, Baldelia ranunculoides, Myriophyllum alterniflorum, Juncus bulbosus, Schoenoplectus pungens, Eleocharis multicaulis, Phragmites australis and Chara fragifera. In total, more than 4,000 individuals were collected from all the water bodies during the spring of 2022 and 2023. Around a hundred genetic markers (microsatellites) were identified and developed for each species.

Results

ISO-SGDC has enabled the development of genetic markers and a  protocol for genotyping them with high precision using high-throughput sequencing. One of the challenges was to identify experimental conditions suitable for the diversity of the plant species studied.
Analysis of the genetic structure of the different species revealed varying levels of genetic diversity depending on the species. Overall, the most common species possess greater genetic diversity, whereas rare and threatened species exhibit lower diversity. A regional pattern of diversity was highlighted for certain species, with strong genetic differentiation despite geographical proximity. A pattern of isolation by distance was identified for all species, but with varying intensity across taxa, 
reflecting contrasting dispersal capabilities.

Analysis of species-genetic diversity correlations (SGDC) reveals a marked scale dependence for all eight species. In B. ranunculoides and S. pungens, the correlation is entirely driven by environmental factors (lake surface area, hydraulic connectivity, natural cover). For the other species, the results suggest that local demographic processes and regional dispersal constraints structure biodiversity in a decoupled manner. 
These results demonstrate that dispersal limitation and environmental filtering processes act jointly to structure the biodiversity of coastal lakes in Aquitaine. The conservation of habitats of Community interest (3110) requires a balanced approach combining local management of habitat quality and regional management of functional connectivity.
This work is a continuation of the multi-partner project Vigie Lacs (https://www.biodiversite-nouvelle-aquitaine.fr/connaitre/enjeux-de-territoire/le-projet-vigie-lacs/). 

This project is eagerly awaited by managers, particularly the South Atlantic National Botanical Conservatory (CBNSA), as part of the coordination and implementation of the national action plan for these species.

Participants

INRAE units involved

• UR EABX - Unité de recherche Écosystèmes aquatiques et changements globaux
• UMR BIOGECO - Biodiversité, gènes et communautés

Partners

• Conservatoire Botanique National Sud-Atlantique
• SIAEBVELG - Syndicat Intercommunal d'Aménagement des Eaux du Bassin Versant et Etangs du Littoral Girondin
• Communauté de Commune des Grands lacs
• Réserve naturelle nationale de l’Étang Noir
• Association Landes Nature