Abstract
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.
Highlights
Homogenization of ecological communities due to intensification of global trade can result in increases in the frequency and intensity of outbreaks of insect species (Samways 1999)
Five-hundred and fifty-two individual winter moths were included after removing individuals from which fewer than 20 of 24 polymorphic microsatellites were amplified as part of this study
This analysis indicated that the populations from northern Fennoscandia are most closely related to the populations from England, Northern Ireland, and Scotland, and not to the populations from southern Fennoscandia or eastern Europe as would be expected if they were the result of contiguous northward range expansion
Summary
Homogenization of ecological communities due to intensification of global trade can result in increases in the frequency and intensity of outbreaks of insect species (Samways 1999). Approximate Bayesian computation (ABC) has become a popular framework to determine both the region of origin of an outbreaking species and its timing of introduction (e.g., Havill et al 2016, Kim et al 2017, Wang et al 2017, Song et al 2018, Javal et al 2019, Lesieur et al 2019) Under this approach, dataset(s) are simulated based on scenarios that include several likely regions of origin, and summary statistics from the sample dataset are compared to those from the simulated datasets to determine the most likely scenario. Limitations aside, ABC has been used to generate credible reconstructions of extremely complex invasion histories (see Lombaert et al 2010, Stone et al 2017 for example), that might not have been possible to disentangle with other methods
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