RAD sequencing helps to unravel the phylogeography of the European spruce bark beetle, Pityogenes chalcographus
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Present distribution and genetic structure of organisms were shaped by past climatic oscillations, e. g., changes in temperature during the Pleistocene. During the last glacial maximum Europe was covered by a thick ice shield in northern regions and high elevation areas, and survival was only possible in glacial refugia. The spruce bark beetle, Pityogenes chalcographus (L.), is an insect with a life cycle closely associated with its main host tree Norway spruce. It is hypothesized that both species shared the same glacial refugia. Postglacial warming led to a range expansion and recolonization of Europe.We reassessed the glacial and postglacial history of P. chalcographusby studying individuals from a huge part of the beetle’s range. We applied ddRADSeq to disentangle the present genetic population structure and to infer glacial and postglacial processes. We confirmed and re-evaluated three glacial refugia in the Apennine-Dinaric region, in the Carpathian Mountains and in the Russian plain. Present genetic structure was strongly influenced by secondary contact during warm periods and the insect’s reproductive and dispersal behavior. Population structure analyses revealed a high level of gene flow across populations leading to a shallow genetic structure and a low level of population differentiation.