Genetic diversity and distribution differ between long-established and recently introduced populations in the invasive mosquito Aedes albopictus. albopictus invasive populations

The Asian tiger mosquito Aedes albopictus, native to South-eastern Asia, is currently the most invasive mosquito in the world. The spatio-temporal dynamics of its expansion through the genetic characterization of invasive populations has been challenged so far by the lack of genetic markers variable enough to infer the genetic structure in recently invaded areas. Here we applied the double-digest Restriction-site Associated DNA sequencing method (ddRADseq) to mosquitoes collected in two invaded areas, Reunion Island (12 populations) and Europe (18 populations), and in one population from the native area (Thailand). We obtained genotypes from 1,356 genome-wide distributed Single Nucleotide Polymorphisms (SNPs). Analyses of genetic diversity, Bayesian clustering, Maximum Likelihood inference and isolation-by-distance tests revealed that these SNPs are appropriate at both local and regional scales, to study the invasion history of the species and contemporary gene flows. We show that Reunion Island and Europe form two distinct genetic clusters, supporting two different and independent invasion histories. Long-established populations (Reunion Island) were genetically more diversified than recently introduced populations (Europe). The largest part of genetic variance was found at the intra-individual level (>87%) and almost all FIS values were positive, suggesting a high level of inbreeding at the local scale. The two invaded areas showed contrasted patterns of genetic structure. Significant isolation-by-distance was found among Reunion Island populations, suggesting that these populations are at the drift-migration equilibrium. In contrast, human-assisted dispersal appeared as the main mechanism in Europe, with bridgehead populations in Italy from which A. albopictus would have spread (France, Slovenia).