Recent progress in the taxonomy of flat bark beetles (Cucujidae), specifically, in the genus Cucujus, has revealed great diversity in subtropical Asia, but the seemingly well-known temperate and boreal taxa need further attention because of their conservation status. Here, we used an integrative approach using morphology, DNA, and species distribution modelling to disentangle phylogenetic relations, verify the number of species, and understand the historical biogeography of Palearctic and Nearctic Cucujus beetles, particularly the C. haematodes species group. Species distinctiveness was supported for C. cinnaberinus, but present-day C. haematodes turned out to be a species complex made up of separate lineages in the western, middle and eastern parts of its Palearctic range. Cucujus muelleri was a member of that complex, being sister to Asian C. haematodes. Moreover, C. haematodes caucasicus was found to be phylogenetically closely related to Italian C. tulliae, and both to be sister to European C. haematodes. North American C. clavipes clavipes and C. c. puniceus resulted to be enough divergent to be considered different species. Interestingly, western American C. puniceus turned out to be closely related to the C. haematodes complex, whereas eastern American C. clavipes constituted a separate lineage, being distantly related to both C. puniceus and C. cinnaberinus. These patterns suggest former trans-continental connections among the ancestors of extant flat bark beetle species. Moreover, a divergent lineage of C. cinnaberinus was found in Calabria, which should be regarded at the very least as a subspecies. The ancestor of C. hameatodes group originated in mid-Miocene, and next, ca. 6.2 Mya, a line leading to C. cinnaberinus had split. Speciation of the American lineages occurred during Pliocene (4.4 Mya for C. clavipes and 3.3 Mya for C. puniceus). Species classified as C. haematodes, C. tulliae and C. muelleri, as well as distinct lineages within C. cinnaberinus split during mid Pleistocene (ca. 1.5 Mya). A comparison of species climatic requirements and their present distribution allowed to identify glacial refugia in south-eastern areas of North America (C. clavipes), south-western areas of North America (C. puniceus), and the Mediterranean and Caspian Sea Basins (European Cucujus species), or south-eastern areas of Asia and the foothills of the central Asian mountains (eastern C. haematodes). Subsequent climatic changes in the Holocene forced these beetles to move their ranges northwards along the coasts of the Pacific (C. puniceus) or Atlantic (C. clavipes), north-eastwards to central, northern, and eastern Europe (C. cinnaberinus and European C. haematodes) or Siberia (Asian C. haematodes). The combined use of molecular, morphological and climatic data allows a comprehensive understanding of the phylogenetic relations and past distributions of Cucujus beetles, highlighting the complexity of C. haematodes species group evolution.

Department of Biology Ecology and Earth Sciences University of Calabria Rende Italy

Department of Biology Faculty of Science University of Hradec Králové Rokitanského 62 500 03 Hradec Králové Czech Republic; Department of Forest Protection and Entomology Faculty of Forestry and Wood Sciences Czech University of Life Sciences Kamýcká 129 165 00 Praha Suchdol Czech Republic

Dipartimento di Scienze Agrarie e Ambientali Università degli Studi di Milano Milan Italy

Dipartimento di Scienze Agrarie e Ambientali Università degli Studi di Milano Milan Italy; BAT Center Interuniversity Center for Studies on Bioinspired Agro environmental Technology University of Napoli Federico 2 Via Università 100 80055 Portici Italy

European Invertebrate Survey Nederland Naturalis Biodiversity Center PO Box 9517 NL 2300 RA Leiden the Netherlands

Fabryczna 1a St PL 57 540 Lądek Zdrój Poland

Faculty of Environmental Sciences and Natural Resource Management Norwegian University of Life Sciences P O Box 5003 NMBU NO 1432 Ås Norway

Forest Research Institute Department of Forest Protection Sękocin Stary Braci Leśnej 3 St PL 05 090 Raszyn Poland

Forest Research Institute Department of Natural Forests Park Dyrekcyjny 6 St PL 17 230 Białowieża Poland

Institute of Entomology Biology Centre CAS Branisovska 31 Ceske Budejovice 370 05 Czech Republic

Institute of Systematics and Evolution of Animals Polish Academy of Sciences Sławkowska 17 St PL 31 016 Kraków Poland

Laboratory of Entomology Institute of Ecology Nature Research Centre Akademijos str 2 LT 08412 Vilnius Lithuania

National Institute of Biology Department of Organisms and Ecosystems Research Večna pot 111 SI 1000 Ljubljana Slovenia

National Museum of Bosnia and Herzegovina Zmaja od Bosne 3 71 000 Sarajevo Bosnia and Herzegovina

Nationalparkverwaltung Bayerischer Wald Stellvertretender Leiter Sachgebietsleiter Naturschutz und Forschung Freyunger Str 2 94481 Grafenau Germany

Nationalparkverwaltung Bayerischer Wald Stellvertretender Leiter Sachgebietsleiter Naturschutz und Forschung Freyunger Str 2 94481 Grafenau Germany; Field Station Fabrikschleichach Department of Animal Ecology and Tropical Biology Biocenter University of Würzburg Glashüttenstraße 5 96181 Rauhenebrach Germany

Naturwissenschaftliche Sammlungen Sammlungs und Forschungszentrum Krajnc Straße 1 6060 Hall in Tirol Austria

Office national des forêts 2 rue de la Forêt BP 50068 F 67131 Schirmeck Cedex France

Scientific Practical Center of the National Academy of Sciences of Belarus for Biological Resources Akademicheskaya Str 27 Minsk 220072 Belarus

University of Wrocław Department of Biodiversity and Evolutionary Taxonomy Przybyszewskiego 65 St PL 51 148 Wrocław Poland

University of Wrocław Department of Invertebrate Biology Evolution and Conservation Przybyszewskiego 65 St PL 51 148 Wrocław Poland

Zoological Department Hungarian Natural History Museum H 1088 Budapest Baross utca 13 Hungary

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