Phylogeography and distribution modelling reveal the history and future of a saproxylic beetle of European conservation concern

Aim: The biogeography of European forests presents many interesting case studies, as inferred from phylogeography, contemporary population genetics, and distribution modelling of saproxylic species. Here, we pose four main hypotheses: (i) the phylogeographic paradigm known for temperate species in Europe is also applicable for saproxylic taxa; (ii) current expansion is occurring only in some genetic lineages; (iii) genetic diversity decreases from east to west, reflecting differences in forest naturalness and management; and (iv) climatic changes will force a northward range shift.Location: Europe.Taxon: The saproxylic beetle, Cucujus cinnaberinus (Scopoli, 1763).Methods: Beetles from 37 locations throughout the species range were genotyped using microsatellites and mtDNA (468 and 237 individuals, respectively). Molecular data were analysed to describe population diversity, structure, and demography. 200 records were used to model distribution based on climate data.Results: mtDNA analyses revealed three clades: the most divergent in Italy and two less distinct in north-western and central - to-southeastern Europe. Microsatellites showed no clear geographic distribution pattern except for a distinct lineage in Italy. The highest genetic diversity was found in southern refugia, in natural forests of Central-Eastern Europe, and in a mixing zone in Pannonia. During the Holocene, the Italian population declined, whereas populations in the rest of Europe showed no clear changes. Distribution models revealed the existence of glacial refugia along the coasts of the Adriatic and Black Seas, and northward dispersal in the Holocene continued in the XXI century.Conclusions: C. cinnaberinus has a complex historical biogeography, discordant with patterns known for temperate or boreal taxa. The current expansion occurs only in populations from mainland Europe, whereas southernmost populations are in decline. Current genetic diversity is shaped by recent forest management, which is the least intensive in Eastern Europe. Climate change will most likely enhance northward dispersal and threaten the survival of the southernmost populations.