ddRAD data for: Multiple introductions and overwintering shape the progressive invasion of Aedes albopictus beyond the Alps

Aedes albopictus originates from Southeast Asia and is considered one of the most invasive species globally. This mosquito is a nuisance and a disease vector of significant public health relevance. In Europe, Ae. albopictus is firmly established and widespread south of the Alps, a mountain range that forms a formidable biogeographic barrier to many organisms. Recent reports of Ae. albopictus north of the Alps raise questions of 1) the origins of its recent invasion, and 2) if this mosquito has established overwintering populations north of the Alps. To answer these questions, we analyzed population genomic data from >4000 genome-wide SNPs obtained through double digest restriction-site associated DNA sequencing. We collected SNPs data from specimens from 6 sites in Switzerland, north and south of the Alps, and analyzed them together with specimens from other 33 European sites, 5 from the Americas, and 5 from its Asian native range. At a global level, we detected 4 genetic clusters with specimens from Indonesia, Brazil and Japan as the most differentiated, whereas specimens from Europe, Hong Kong and USA largely overlapped. Across the Alps, we detected a weak genetic structure and high levels of genetic admixture, supporting a scenario of rapid and human-aided dispersal along transportation routes. While the genetic pattern suggests frequent re-introductions from Italian sources into Switzerland, the recovery of a pair of full siblings in two consecutive years in Strasbourg, France, suggests the presence of an overwintering population north of the Alps. The finding of overwintering populations of Ae. albopictus north of the Alps and the expansion patterns points to an increased risk of further northwards expansion and the need for increased surveillance of mosquito populations in northern Europe.