Population structure and interspecific hybridisation of two invasive blowflies (Diptera: Calliphoridae) following replicated incursions to New Zealand
Rates of biological invasion are increasing globally, with associated negative effects on native biodiversity and ecosystem services. Among other genetic processes, hybridisation can facilitate invasion by producing new combinations of genetic variation that increase adaptive potential and associated population fitness. Yet the role of hybridisation (and resulting gene flow) in biological invasion for invertebrate species is under-studied.Calliphora hilli and Calliphora stygia are blowflies proposed to have invaded New Zealand separately from Australia c. 1779-1841 that are now widespread throughout the country. Here, we analysed genome-wide single nucleotide polymorphism (SNP) data, generating genotyping-by-sequencing data for 154 individuals collected from 24 populations across New Zealand and Australia to assess the extent of gene flow and hybridisation occurring within and between these blowflies and to better understand their overall population structure.We found that New Zealand populations of both species had weak genetic structure, suggesting high gene flow and an absence of dispersal limitations across the country. We also found evidence that interspecific hybridisation is occuring in the wild between C. hilli and C. stygia in both the native and invasive range, and that intraspecific admixture is occurring among populations at appreciable rates. Collectively, these findings provide new insights into the population structure of these two invasive invertebrates and highlight the potential importance of hybridisation and gene flow in biological invasion.