Using high-density SNP genotyping to determine the origin of wild boar dispersers outside the geographic range margins in Norway

Mammalian dispersal is characterized by long distance movements, and
whether dispersal is sex-dependent and occurs at pre-saturation densities
affects colonization speed and concurrent pathogen spread. In Scandinavia,
Sweden classifies wild boar (Sus scrofa) as a native species and retains
high densities, while Norwegian authorities consider them an alien
invasive species and maintain the population at a minimum. With a long
shared border and the recent detection of African swine fever (ASF) in
Sweden, long distance dispersal of wild boar into Norway is a concern.
Using high-density single nucleotide polymorphism (SNP) analysis of
relatedness among 192 wild boar distributed across Sweden and Norway, we
report sex and determined the likely origin of seven dispersing
individuals detected far outside of the current Norwegian range margins.
Dispersal distances varied from 61 to 431 km (mean = 230) and all seven
dispersers were males, which reduces the likelihood of successful
reproduction and establishment. Five of the wild boar originated from the
low-density population at the colonization border in Norway, indicating
pre-saturation dispersal. Sweden is of interest given the risk of pathogen
spread. However, in the current epidemiological situation, we nevertheless
consider it very unlikely that ASF will enter Norway by long-distance wild
boar dispersal.