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

Abstract

Invasive alien species are a significant threat to both economic and ecological systems. Identifying the 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.

Influence of intrinsic and extrinsic attributes on neonate survival in an invasive large mammal

“…The wild pig population on the SRS was descended from feralized domestic pigs released after the private land was converted to a government facility in 1950 44 . Later introduction of wild boar and wild boar and feral pig hybrids led to introgression of wild boar genes into the SRS wild pig population 22 , 44 . Hybridization on the SRS led to high phenotypic variability, especially in pelage coloration within and between litters (Fig.…”

“…Wild pigs ( Sus scrofa ) are among the most widely distributed and damaging invasive species worldwide 20 . Typically comprised of mixed ancestry of wild boar and domestic pigs 21 , 22 , wild pigs are ecological generalists that are highly adaptable with the greatest reproductive capacity of any mammal of their size, and thus are able to thrive and expand quickly in new environments. Globally, wild pig populations have rapidly increased in abundance and distribution over the past few decades 23 .…”

Population genomics for wildlife conservation and management

“…Hybridization and admixture can also have negative consequences for fitness and local adaptation in wildlife species, particularly with massive increases in human‐facilitated movement of organisms (Allendorf et al., 2001). One example is species invasions facilitated by hybridization (e.g., feral swine, Sus scrofa ; Smyser et al., 2020), which can negatively impact native wildlife populations. More directly, hybridization between westslope cutthroat trout ( Oncorhynchus clarkii lewisi ) and the widely introduced rainbow trout ( O. mykiss ) in western North America reduces fitness of the native species (Muhlfeld et al., 2009).…”

Loci Associated With Antibody Response in Feral Swine (Sus scrofa) Infected With Brucella suis

“…In the United States (U.S.) there are ∼6 million invasive feral swine (Sus scrofa), which are defined as any released or escaped domestic pigs, Eurasian wild boars, or hybrids of the two (1,2). Both the abundance of feral swine and extent of the geographic range have increased rapidly over the past 30 years due to the high reproductive potential of the species, limited predation pressure, abundance of food (both native flora and fauna and agricultural products), and human-mediated introduction into uninvaded habitats (3,4).…”