Postglacial genetic legacies and climate-driven demography inform conservation of silver fir

BACKGROUND AND AIMS: This study explores the genetic diversity and past range dynamics of silver fir (Abies alba) with the objective of delineating the past demography of the species, the main postglacial colonization pathways and the current vulnerability of past glacial refuges. METHODS: We applied restriction site-associated DNA sequencing (RAD-seq) to 26 A. alba populations to explore their phylogeographic structure and historical demographic changes. KEY RESULTS: Three lineages were identified. One comprised populations from the southern range, whereas northern populations formed two lineages with subtle genetic differentiation between western and eastern populations. Northern Balkan and north-eastern Apennine samples clustered within introgression zones at the intersection of postglacial recolonization routes, consistent with their intermediate geographic positions. Demographic analyses indicated that southern populations remained relatively stable as glacial refugia, whereas northern populations experienced population declines during the middle Pleistocene associated with glaciations. Although the demographic events that shaped the current spatial structure of genetic diversity of silver fir go back to the Pleistocene, human pressure during the Holocene likely led to an abrupt range decline. CONCLUSIONS: We present a timely and broadly applicable framework for delineating the phylogeographic lineages of silver fir, leveraging the high resolution provided by SNP markers to identify major genetic discontinuities, contact zones and refugial areas. Inferences of past demographic dynamics indicate that certain rear-edge populations warrant priority in conservation strategies.