Phylogeography of a widely distributed species reveals a cryptic assemblage of distinct genetic lineages needing separate conservation strategies
Résumé
Genetic structure in broadly distributed herbs may be shaped by past climate events, leading to distinct genetic lineages, and possibly to different Evolutionary Significant Units (ESUs). We identified the potential glacial refugia, postglacial (re)colonization routes, contact zones and ESUs in the widespread but locally rare Silene nutans to propose appropriate conservation strategies related to migration history-related genetic structure. We sequenced four plastid DNA markers from 136 populations covering S. nutans European distribution range. We built a network on concatenated sequences using statistical parsimony and performed Bayesian and Maximum Likelihood analyses to build a phylogenetic tree. Haplotype genetic diversity and between-population differentiation (G(ST), N-ST) were calculated. Based on 23 plastid haplotypes, populations were ascribed to seven strongly differentiated genetic lineages. Potential refugia were identified: in the Iberian and Italian Peninsulas, expanding to south-western France and the Alps, respectively; in south-central France, reaching England and Belgium; an eastern refugium, following a north-westward expansion; in the Balkans, expanding to north-eastern Italy, and in the Carpathians. Several contact zones were identified. Silene nutans consists of a cryptic assemblage of genetically distinct taxa, with at least seven ESUs. Evaluating the distribution range, the abundance, and the conservation status of each ESU is necessary for the preservation of the S. nutans species complex at European and regional levels. Ex situ conservation and genetic restoration involving plant translocations must consider the phylogeographic history and the distinct genetic lineages to avoid the introduction of poorly adapted plants and outbreeding depression leading to non-viable hybrid progeny, especially in contact zones.