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

Abstract

Austrian dragonhead (Dracocephalum austriacum), a rare species of steppe and mountain 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 fewer than 90 small and spatially isolated populations. Despite legal protection, the species is threatened by habitat fragmentation and environmental change. We genotyped nearly all known populations across the species′ range using the DArTseq method to provide a genomic basis for conservation planning. We analysed key indices of genetic diversity, their spatial patterns, and phylogenetic relationships using genome-wide SNP data. To reconstruct the species’ phylogeographical history, we also conducted ecological niche modelling, demographic history inference and divergence time estimation. Our results reveal five geographically restricted genetic lineages that can be regarded as evolutionarily significant units. The most distinct lineage in the eastern Pyrenees exhibits signatures of long-term isolation and retention of ancestral polymorphism. In contrast, the remaining four lineages are of more recent origin and reflect a phylogeographic pattern consistent with gradual lineage diversification associated with Pleistocene habitat dynamics. The divergence between the two most distinct genetic lineages likely began during the Early Pleistocene, while a subsequent phase of range expansion and lineage diversification occurred during the Middle to Late Pleistocene. This pattern suggests that intraspecific differentiation was strongly influenced by Pleistocene climatic oscillations. Overall, genomic diversity is low and relatively uniform across the species′ range. Estimates of effective population size indicate that most populations are likely viable only in the short term, underscoring the need for coordinated conservation efforts across the species′ distribution.