Mixed ancestry from wild and domestic lineages contributes to the rapid expansion of invasive feral swine

Invasive alien species are a significant threat to both economic and
ecological systems.  Identifying processes that give rise to
invasive populations is essential for implementing effective control
strategies.  We conducted an ancestry analysis of invasive feral
swine (Sus scrofa, Linnaeus, 1758), a highly destructive ungulate that is
widely distributed throughout the contiguous United States, to describe
introduction pathways, sources of newly-emergent populations, and
processes contributing to an ongoing invasion.  Comparisons of
high-density single nucleotide polymorphism genotypes for 6,566 invasive
feral swine to a comprehensive reference set of S. scrofa revealed that
the vast majority of feral swine were of mixed ancestry, with dominant
genetic associations to Western heritage breeds of domestic pig and
European populations of wild boar.  Further, the rapid expansion
of invasive feral swine over the past 30 years was attributable to
secondary introductions from established populations of admixed ancestry
as opposed to direct introductions of domestic breeds or wild
boar.  Spatially-widespread genetic associations of invasive
feral swine to European wild boar deviated strongly from historical S.
scrofa introduction pressure, which was largely restricted to domestic
pigs with infrequent, localized wild boar releases.  The
deviation between historical introduction pressure and contemporary
genetic ancestry suggests wild boar-hybridization may contribute to
differential fitness in the environment and heightened invasive potential
for individuals of admixed domestic pig-wild boar ancestry.