Spatial population genomics of a recent mosquito invasion

Population genomic approaches can characterise dispersal across a single generation through to many generations in the past, bridging the gap between individual movement and intergenerational gene flow. For recent biological invasions, simultaneous sampling of populations across a range of spatial scales can be used to assess current and past movements, while overcoming complications from stratified dispersal and high regional coancestry. Here we investigate a 2004 invasion involving Aedes albopictus (the Asian tiger mosquito) in the Torres Strait Islands (TSI), Australia. We sampled mosquitoes from 13 TSI villages simultaneously and genotyped 373 mosquitoes at genome-wide single nucleotide polymorphisms (SNPs): 331 from the TSI, 36 from Papua New Guinea (PNG), and 4 incursive mosquitoes detected south of the cordon sanitaire established in 2008 to stop the invasion reaching the Australian mainland. Within villages, spatial genetic structure varied substantially but overall displayed isolation by distance and a neighbourhood size of 232-577. Close kin dyads revealed recent movement between islands 31-203 km apart, and deep learning inference of incursion pathways showed Ae. albopictus had crossed the cordon sanitaire from both adjacent and non-adjacent islands. Private alleles and a coancestry matrix indicated direct gene flow from PNG into nearby islands. Outlier analyses also detected four linked alleles introgressed from PNG, with the alleles surrounding 12 resistance-associated cytochrome P450 genes. By treating dispersal as both an intergenerational process and a set of discrete events, we describe a highly interconnected invasive system. The movement of mosquitoes between distant islands and potential "genetic invasion" of insecticide resistance alleles are important management concerns.