Abstract: Reconstructing the geographic origins of invasive
species is critical for establishing effective management strategies.
Frequently, molecular investigations are undertaken when the source
population is not known, however; these analyses are constrained both by
the amount of diversity present in the native region and by changes in
the genetic background of the invading population following bottlenecks
and/or hybridization events. Here we explore the geographical origins of
the invasive winter moth (Operopthera brumata L.) that has caused
widespread defoliation to forests, orchards, and crops in four discrete
regions: Nova Scotia, British Columbia, Oregon, and the northeastern
United States. It is not known whether these represent independent
introductions to North America, or “stepping stone” spread among
regions. Using a combination of Bayesian assignment and approximate
Bayesian computation methods, we analyzed a population genetic dataset
of 24 polymorphic microsatellite loci. We estimate that winter moth was
introduced to North America on at least four occasions, with the Nova
Scotian and British Columbian populations likely being introduced from
France and Sweden, respectively; the Oregonian population likely being
introduced from either the British Isles or northern Fennoscandia; and
the population in the northeastern United States likely being introduced
from somewhere in Central Europe. To our surprise, we found that
hybridization has not played a large role in the establishment of winter
moth populations even though previous reports have documented widespread
hybridization between winter moth and a native congener. We discuss the
impact of genetic bottlenecks on analyses meant to determine region of
origin.
Keywords: Approximate Bayesian computation, region of origins,
invasive species, biosecurity