Phylogeography of the medically important mosquito Aedes (Ochlerotatus) vigilax (Diptera: Culicidae) in Australasia

Aim Within Australia the Carpentaria Barrier has been identified as an important biogeographical barrier. Here we test this long-standing hypothesis using a medically important mosquito, Aedes (Ochlerotatus) vigilax. Location We obtained samples of Ae. vigilax from throughout its Australian distribution and from New Caledonia. Methods We constructed a distributional database from 602,417 specimens and obtained sequence data from 66 female specimens from 16 localities. The distributional database of Ae. vigilax comprised historical data from 13 organizations and was used to develop our molecular sampling strategy. Genetic structure within Ae. vigilax was examined via haplotype networks, FST values, analysis of molecular variance and neutrality test statistics based on one mitochondrial (cytochrome c oxidase subunit I, COI) and two nuclear (alpha amalyse and zinc finger) loci. The historical demography of Ae. vigilax was investigated using extended Bayesian skyline plot (EBSP) methods, with past migration rates estimated using migrate. Results We identified three distinct lineages within Ae. vigilax; however, two of the three lineages show a large distributional overlap across the Carpentaria Barrier. The mitochondrial locus suggested a pattern of significant genetic differentiation, with high FST values, significant genetic differentiation within the COI locus, and significantly more variation between the lineages than within. A higher number of migrants per generation were estimated for the overlapping lineages and both the neutrality test statistics and EBSP suggested the occurrence of post-population expansion in these lineages. Main conclusions Significant deviation from genetic neutrality, in combination with estimates of migration and the demographic history of Ae. vigilax lineages, suggests that the incongruence of the Ae. vigilax phylogeny with the hypothesized Carpentaria Barrier could be attributed to the separation of eastern and western populations of Ae. vigilax around 770 ka and subsequent secondary contact within the last 100 kyr. Sea-level and precipitation fluctuations within the Carpentaria area during the late Quaternary could have facilitated the current biogeographical patterns of Ae. vigilax. Mosquitoes represent one of the most medically important insect groups; however, understanding the factors that influence past and present distributions of mosquitoes is critical in the face of a range of emerging arboviruses.