Introgression of an isolated Primula lineage suggests the existence of a glacial refugium in the Écrins range (Southwestern French Alps)

The species-richness of the flora in the European Alps results from complex interactions between geographical, climatic and environmental factors. In this study, we focus on a complex of closely related Alpine plants: Primula hirsuta, P. pedemontana and their relatives. Using a large DNA dataset of thousands of single-nucleotide polymorphisms sequenced across 149 individuals spanning all the western Alps, we refine phylogenetic relationships in this clade and explore the evolutionary origins of a mysterious lineage found in one valley of the Écrins range (France): the Valgaudemar. In particular, we demonstrate that this lineage did not originate from a simple allopatric divergence, but from an isolated lineage related to Primula pedemontana, which later got introgressed by P. hirsuta. This leads us to develop a phylogeographic scenario explaining the origins of the Valgaudemar lineage, and shed light on a potential glacial refugium in the south of the Écrins range. We believe this study takes part in the deep understanding of the origins of endemism in the European Alps and more generally of the maintaining of species diversity.