Postglacial recolonization shaped the genetic diversity of the winter moth (Operophtera brumata) in Europe

Abstract

Changes in climate conditions, particularly during the Quaternary climatic oscillations, have long been recognized to be important for shaping patterns of species diversity. For species residing in the western Palearctic, two commonly observed genetic patterns resulting from these cycles are as follows: (1) that the numbers and distributions of genetic lineages correspond with the use of geographically distinct glacial refugia and (2) that southern populations are generally more diverse than northern populations (the “southern richness, northern purity” paradigm). To determine whether these patterns hold true for the widespread pest species the winter moth (Operophtera brumata), we genotyped 699 individual winter moths collected from 15 Eurasian countries with 24 polymorphic microsatellite loci. We find strong evidence for the presence of two major genetic clusters that diverged ~18 to ~22 ka, with evidence that secondary contact (i.e., hybridization) resumed ~ 5 ka along a well‐established hybrid zone in Central Europe. This pattern supports the hypothesis that contemporary populations descend from populations that resided in distinct glacial refugia. However, unlike many previous studies of postglacial recolonization, we found no evidence for the “southern richness, northern purity” paradigm. We also find evidence for ongoing gene flow between populations in adjacent Eurasian countries, suggesting that long‐distance dispersal plays an important part in shaping winter moth genetic diversity. In addition, we find that this gene flow is predominantly in a west‐to‐east direction, suggesting that recently debated reports of cyclical outbreaks of winter moth spreading from east to west across Europe are not the result of dispersal.

Identification of winter moth (Operophtera brumata) refugia in North Africa and the Italian Peninsula during the last glacial maximum

“…In that work, we genotyped field‐collected individuals from across Europe with 24 highly polymorhic microsatellie loci. In contrast to mtDNA sequence data that showed limited biogeographic structure between winter moth populations, we found evidence that individuals could be assigned to either an eastern or a western European genetic lineage, with a clear hybrid zone in central Europe (Andersen et al, ). Using approximate Bayesian computation (ABC) methods, we also hypothesized that the contemporary genetic diversity of European populations of this species was largely shaped by its retreat to refugia in the Iberian, Balkan, and Caucasus regions, and by hybridization between the Iberian and Balkan lineages postrecolonization.…”

“…We used the results from Andersen et al () to establish the relationships among the other European populations. Andersen et al () found strong support for the German lineage to be the result of admixture between the Spanish and Serbian lineages after the LGM. The authors were unable, however, to conclude whether the Serbian and Georgian lineages diverged before or after the divergence of the Spanish lineage, as these two scenarios received equivocal results.…”

“…The authors were unable, however, to conclude whether the Serbian and Georgian lineages diverged before or after the divergence of the Spanish lineage, as these two scenarios received equivocal results. To reduce complexity in scenario design, here we use a tree with the Spanish lineage diverging prior to the divergence of the Serbian and Georgian lineages [Scenario 7 from Andersen et al ()] as our root tree. Three scenarios (Figure ) were compared to determine whether the Italian population was most closely related to the Spanish, Serbian, or Georgian populations by generating a reference table based on three million simulated datasets (one million per scenario).…”

“…Previously, we examined the use of glacial refugia during the last glacial maximum (LGM) by winter moth (Andersen et al, ). In that work, we genotyped field‐collected individuals from across Europe with 24 highly polymorhic microsatellie loci.…”

“…Therefore, in this study we obtain new winter moth samples from Tunisia, Italy, and additional specimens from Spain, to further explore the biogeographic history of winter moth and its use of potential glacial refugia during the LGM. Specifically, our research objectives were as follows: (a) to genotype winter moth individuals collected in potential glacial refugia not sampled in Andersen et al (; i.e., Southern Italy and North Africa), and (b) to determine whether outbreaking populations of winter moth in Tunisia represent a native population dating back to the LGM or whether they were recently introduced to the region, and if so from where.…”