Insular East Asia pig dispersal and vicariance inferred from Asian wild boar genetic evidence

The Formosan wild boar () is an endemic subspecies in Taiwan. Understanding the origins and spread of the Formosan wild boar could help clarify East Asian wild boar dispersion. Although in situ domestication of the wild boar occurred at a number of domestication centers across East Asia, corroborating archaeological and genetic evidence of pig domestication on Taiwan is lacking, leading to domestication being described as cryptic. This characterization applies to the Lanyu pig-a domestic pig breed found on Taiwan. To better understand pig domestication, this study examines the sympatric Formosan wild boar and domestic Lanyu pig to build a model of potential wild boar domestication on Taiwan and elucidate wild boar domestication patterns in the region. To this end, a comprehensive phylogenetic study of the Formosan wild boar and the Lanyu pig was conducted on animals sourced from Taiwan, Lanyu, and the Philippines. Phylogenetic analyses were conducted using full mitochondrial control-region sequences from 345 wild boars and domestic pigs. These were studied in concert with existing reports on 206 Asian wild boars. Genetic characteristics and Bayesian phylogenetic tree results identified 2 wild boar lineages of remote phylogenetic relationship. These were Formosan wild boar lineage (FWBL) and Formosan wild boar with Lanyu sign lineage (FWBLYL). Molecular clock analyses indicate that FWBLYL diverged earlier than other insular East Asia wild boars and show that FWBLYL and FWBL diverged approximately 0.60 million years ago. This result supports boars of FWBLYL being the earliest wild boars to have spread and become isolated in insular East Asia. In addition, the study proposes 6 Asian wild boar dispersion routes during glacial periods. At least 3 of these events occurred in insular East Asia with subsequent geographical isolation after glacial recession. This isolation potentially led to allopatric differentiation of wild boar subspecies. Also, the similar genetic signature and phylogenetic uniqueness of Lanyu pigs to wild boars of FWBLYL suggests such wild boars were the wild ancestor of domestic Lanyu pigs. This result indicates potential in situ domestication occurring on Taiwan. Finally, pigs possessing FWBLYL's genetic signatures were continuously distributed among Taiwan, Lanyu, and the Philippines. This pattern may signify human-mediated pig dispersal routes.