Population genetics of the malaria vector Anopheles aconitus in China and Southeast Asia

Abstract

Anopheles aconitus is a well-known vector of malaria and is broadly distributed in the Oriental Region, yet there is no information on its population genetic characteristics. In this study, the genetic differentiation among populations was examined using 140 mtDNA COII sequences from 21 sites throughout Southern China, Myanmar, Vietnam, Thailand, Laos and Sri Lanka. The population in Sri Lanka has characteristic rDNA D3 and ITS2, mtDNA COII and ND5 haplotypes, and may be considered a distinct subspecies. Clear genetic structure was observed with highly significant genetic variation present among population groups in Southeast Asia. The greatest genetic diversity exists in Yunnan and Myanmar population groups. All population groups are significantly different from one another in pairwise Fst values, except Northern Thailand with Central Thailand. Mismatch distributions and extremely significant F(s) values suggest that the populations passed through a recent demographic expansion. These patterns are discussed in relation to the likely biogeographic history of the region and compared to other Anopheles species.

Fig. 1

Localities collected for populations of An. aconitus in China, Myanmar, Vietnam, Thailand, Laos and Sri Lanka. The 22 populations with samples collected are shown with filled circles and divided into 9 population groups (in separate circles) based on their geographical distributions. The sites without samples encountered are shown with empty circles. The top-left frame shows the previously suggested distribution area of the species.

Fig. 2

Maximum-likelihood trees of sequences of mtDNA COII and ND5 genes and rDNA D3, D2 and ITS2 loci (An. filipinae and An. pampanai as outgroup taxa), showing their variation within An. aconitus and the subdivision of the Sri Lankan population to subspecies. The sample names indicate their COII haplotypes and localities. Bootstrap percentages of 1000 replicates calculated with the maximum parsimony method are shown above the branches where they exceed 50%. Branch lengths are proportional to the number of character differences.

Fig. 3

Genealogical relationships among 46 COII haplotypes of An. aconitus estimated by TCS (Clement et al., 2000). The size of a circle corresponds to the COII haplotype frequency, and a unit branch represents one mutation. Small ovals indicate COII haplotypes that were not observed.

Fig. 4

Observed mismatch distributions among pairwise differences among haplotypes for all populations except Sri Lanka, which is closely unimodal and fits to a Poisson distribution (χ²: s² = 1.32 and P < 0.001).