Genomic insights into ancestry and genetic structure of wild boar in northern Europe

The distribution and genetic structure of ungulates are shaped by a mixture of ancient and recent processes, reflecting both natural colonization and human-mediated translocations following the last glaciation, and, in some cases, hybridization with domestic forms. Here, we present the first comprehensive analysis of the genetic structure of wild boar Sus scrofa (n = 101) in northern Europe, analysed in relation to samples from continental Europe, Asia and North Africa (755 wild boar and 273 domestic pigs, S. domesticus). We tested the consistency of historical accounts suggesting that wild boar colonized Finland from the Baltic states via Russia, whereas the Swedish and Norwegian population originated from animals that escaped from Swedish game parks and enclosures in the 1970s, with ancestry from Germany or Central Europe. As predicted, wild boar from Finland clustered with populations from the Baltic region, whereas individuals from Sweden and Norway formed a distinct genetic cluster most closely related to wild boar from western Europe. We also corroborated historical records indicating multiple release sites in Sweden, which are reflected in southern, northwestern, and eastern genetic clusters. Wild boar that colonized Norway originated from both the eastern and northwestern Swedish clusters. Populations in Norway and Sweden exhibited relatively low genomic diversity and signatures of recent inbreeding. We detected evidence of minor introgression from domestic pigs in wild boar from Finland, Sweden, and Norway. Wild boar is a controversial species due to its high invasive potential and epidemiological importance as a reservoir for notifiable diseases such as African swine fever. We discuss how our results inform the differing management status (native vs. invasive) in the Fennoscandian countries. Overall, our study highlights the complex history of large mammals at the northern edge of their European distribution, shaped by an interplay of natural expansion and human-mediated translocations.