Pleistocene genetic connectivity in a widespread, open-habitat-adapted mosquito in the Indo-Oriental region

Aim The environmental effect of Pleistocene climatic change in the Indo-Oriental region has resulted in allopatric fragmentation and the generation of diversity in forest-associated species. The aim of this study was to determine the extent to which Pleistocene climatic change has resulted in the fragmentation and speciation of an open-habitat-adapted mosquito, Anopheles vagus s.l., across its range.

Location Anopheles vagus s.l. was sampled across the Indo-Oriental region.

Methods We generated 116 mitochondrial cytochrome c oxidase subunit I (COI) and 121 nuclear internal transcribed spacer 2 (ITS2) DNA sequences from 18 populations. Relationships between mitochondrial haplotypes were reconstructed using minimum spanning networks, and population structure was examined using analyses of molecular variance. The population history, including lineage divergence times, population expansion and gene flow, was inferred using beast and the isolation with migration (IM) model.

Results There was no evidence to support the presence of the endemic Philippines species, A. limosus; instead, Philippine populations were closely related to, and derived from, A. vagus on the eastern Southeast Asian mainland. The most distinct populations were those from Java and East Timor, which differed from all other populations by all individuals having a 4-bp insertion in the ITS2 sequence. The corresponding mitochondrial haplotypes had an estimated divergence time of 2.6 Ma [95% confidence interval (CI) 1.9-3.6 Ma]. Haplotype networks and analysis of molecular variance for COI supported western (Sri Lanka, India and Myanmar) and eastern (Thailand, Singapore, Cambodia, Vietnam and the Philippines) population groupings. This grouping structure results from the divergence of an eastern and a western mitochondrial lineage, estimated to have occurred 0.37 Ma (95% CI 0.26-0.55 Ma). Subsequent migration from the east to the west (0.16 Ma) is inferred to have created an admixture zone in Myanmar and Thailand.

Main conclusions With the possible exception of populations from Java and East Timor, A. vagus appears to be one widespread genetically diverse taxon across its extensive range. The abundance of grassland during long interglacial periods may have facilitated population connectivity and range expansion across the Oriental and western Australasian regions.