Tracing the evolutionary history of Dracocephalum austriacum: Insight from population genomics and species distribution modelling

Austrian dragonhead ( Dracocephalum austriacum ), a rare species of mountain steppe/steppe habitats, has a highly fragmented distribution across its entire range. Due to its narrow ecological requirements, it inhabits relict habitats that are increasingly threatened by climate change, human disturbance and ongoing succession. Across Europe, the species persists in less than 90 small and spatially isolated populations. Although it is legally protected, without targeted conservation efforts and tailored rescue programmes, its future remains uncertain. Therefore, we genotyped almost all of the known populations across the species’ range using the DArTseq method to apply these data to support ongoing direct conservation efforts. We analysed key indices of genetic diversity, their spatial patterns, and phylogenetic relationships. To reconstruct the species' phylogeographical history, we also conducted MaxEnt modelling of habitat suitability. Our results reveal five geographically restricted genetic lineages considered as evolutionary significant units. The most distinct lineage in the eastern Pyrenees exhibits signs of long-term isolation and retention of ancestral polymorphism. In contrast, the remaining four lineages are of more recent origin and reflect a clear phylogeographic pattern of westward expansion from the Caucasus. The divergence between the two most distinct genetic lineages likely began during the Last Interglacial period, while a subsequent wave of east-to-west colonisation during the Last Glacial Period introduced newer lineages. Overall, genomic diversity is low and relatively uniform across the species’ range. Effective population size estimates suggest that most populations are only viable in the short term.