Natural selection on feralization genes contributed to the invasive spread of wild pigs throughout the United States.

Despite a long presence in the contiguous United States (US), the distribution of invasive wild pigs (Sus scrofa × domesticus) has expanded rapidly since the 1980s, suggesting a more recent evolutionary shift towards greater invasiveness. Contemporary populations of wild pigs represent exoferal hybrid descendants of domestic pigs and European wild boar, with such hybridization expected to enrich genetic diversity and increase the adaptive potential of populations. Our objective was to characterize how genetic enrichment through hybridization increases the invasiveness of populations by identifying signals of selection and the ancestral origins of selected loci. Our study focused on invasive wild pigs within Great Smoky Mountains National Park, which represents a hybrid population descendent from the admixture of established populations of feral pigs and an introduction of European wild boar to North America. Accordingly, we genotyped 881 wild pigs with multiple high-density single-nucleotide polymorphism (SNP) arrays. We found 233 markers under putative selection spread over 79 regions across 16 out of 18 autosomes, which contained genes involved in traits affecting feralization. Among these, genes were found to be related to skull formation and neurogenesis, with two genes, TYRP1 and TYR, also encoding for crucial melanogenesis enzymes. The most common haplotypes associated with regions under selection for the Great Smoky Mountains population were also common among other populations throughout the region, indicating a key role of putatively selective variants in the fitness of invasive populations. Interestingly, many of these haplotypes were absent among European wild boar reference genotypes, indicating feralization through genetic adaptation.

Parasite Prevalence in Feral Swine (Sus scrofa) from the Great Smoky Mountains National Park, USA.

Feral swine (Sus scrofa) are an introduced species to the Great Smoky Mountains National Park (GSMNP), US, and serve as carriers of several diseases that are considered a threat to other wildlife, domestic animals, and humans. During 2013 and 2015, fecal samples from 67 feral swine from the GSMNP within both Tennessee and North Carolina, US, were opportunistically collected as part of a feral swine removal program and submitted to the University of Tennessee College of Veterinary Medicine, Knoxville, Tennessee, for parasite screening by centrifugal sugar flotation. Ten taxa from the phyla Acanthocephala, Apicomplexa, and Nematoda were identified: Ascaris spp., Strongylid-type spp., Capillaria spp., Trichuris suis, Metastrongylus spp., Macracanthorhynchus spp., Coccidia, Sarcocystis spp., and Cryptosporidium spp. In 98.5% of samples, at least one parasite was found. No differences in parasite prevalence or species diversity were noted based on state of collection (Tennessee or North Carolina), sex, or age. The high prevalence of gastrointestinal parasites in these feral swine, some of which are zoonotic, represents a potential public health risk as well as a concern for free-range swine farmers.

Toxoplasma gondii seroprevalence and genotype diversity in select wildlife species from the southeastern United States.

BACKGROUND: Toxoplasma gondii is a widespread protozoan parasite that infects humans and other animals. Previous studies indicate some genotypes of T. gondii are more frequently isolated in wildlife than agricultural animals, suggesting a wild/feral animal diversity model. To determine seroprevalence and genetic diversity of T. gondii in southeastern US wildlife, we collected sera from 471 wild animals, including 453 mammals and 18 birds, between 2011 and 2014. These serum samples were assayed for T. gondii infection using the modified agglutination test (MAT). Heart or tongue tissues from 66 seropositive animals were bioassayed in mice and 19 isolates were obtained. The isolated parasites were genotyped by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method employing 10 genetic markers. RESULTS: One hundred and ninety-six of 471 samples (41.6%) had a titer ≥1:32 and were considered positive for T. gondii infection. Of 453 mammals, 195 (43%) were seropositive, whereas only one (5.6%) of 18 birds was seropositive. The seroprevalence in mammals was significantly higher than in the birds. Mammalian hosts with adequate samples size (≥ 20) comprised white-tailed deer (n = 241), feral hogs (n = 100), raccoons (n = 34) and coyotes (n = 22), with seroprevalences of 41.0%, 51.0%, 50.0% and 72.7%, respectively. Coyotes had significantly higher seroprevalence than the white-tailed deer. Genotyping revealed five distinct genotypes, including the ToxoDB PCR-RFLP genotype #5 (a.k.a type 12) for 15 isolates, genotype #3 (a.k.a. type II) for 1 isolate, and genotypes #154, #167 and #216, each for 1 isolate. The results showed moderate to high infection rates of T. gondii in white-tailed deer, feral hogs, raccoons and coyotes. Genotyping results indicated limited genetic diversity and a dominance of genotype #5, which has been reported as a major type in wildlife in North America. CONCLUSIONS: We conclude that T. gondii infection is common in game animals (white-tailed deer and feral hogs) in the southeastern US, which may pose a food safety risk to humans. Further research is necessary to understand T. gondii transmission from wildlife to farm animals and humans.