Winter moth in Scandinavia: structure file

The frequency and severity of outbreaks by pestiferous insects is
increasing globally, likely as a result of human-mediated introductions of
non-native organisms. However, it is not always apparent whether an
outbreak is the result of a recent introduction of an evolutionarily naïve
population, or of recent disturbance acting on an existing population that
arrived previously during natural range expansion.  Here we use
approximate Bayesian computation to infer the colonization history of a
pestiferous insect, the winter moth, Operophtera brumata L. (Lepidoptera:
Geometridae), which has caused widespread defoliation in northern
Fennoscandia. We generated genotypes using a suite of 24 microsatellite
loci and find that populations of winter moth in northern Europe can be
assigned to five genetically distinct clusters that correspond with 1)
Iceland, 2) the British Isles, 3) Central Europe and southern
Fennoscandia, 4) Eastern Europe, and 5) northern Fennoscandia. We find
that the northern Fennoscandia winter moth cluster is most closely related
to a population presently found in the British Isles, and that these
populations likely diverged around 2,900 years ago. This result suggests
that current outbreaks are not the result of a recent introduction, but
rather that recent climate or habitat disturbance is acting on existing
populations that may have arrived to northern Fennoscandia via pre-Roman
traders from the British Isles, and/or by natural dispersal across the
North Sea likely using the Orkney Islands of northern Scotland as a
stepping-stone before dispersing up the Norwegian coast.