Estimates of gene flow among Anopheles maculatus populations in Thailand using microsatellite analysis.

We report an analysis of seven microsatellite loci in eight populations of Anopheles maculatus mosquitoes dispersed over a distance of approximately 1,100 km in Thailand. A wide spectrum of genetic variability, with mean heterozygosities ranging from 0.738 to 0.847 were found. Based on microsatellite analysis, geographic populations of An. maculatus can be grouped into two clusters; one includes upper and lower northern populations that extend from approximately 11 degrees to 16 degrees north latitude, and the other (southern populations) extends south from about 7 degrees to 6 degrees north latitude. Wright's F(ST) and Slatkins's R(ST) for all seven microsatellite loci indicated low estimates of differentiation among all populations (mean values of F(ST) and R(ST) = 0.0406 and 0.051, respectively, corresponding to the Nm values of 5.91 and 4.65, respectively), and suggested that gene flow occurs among populations. However, there is some restriction of gene flow between the northern and southern populations. Geographic barriers could be limiting factors for greater gene flow between populations.

Microsatellite polymorphism in Anopheles maculatus, a malaria vector in Thailand.

Dinucleotide microsatellites were characterized from Anopheles maculatus, a species of mosquito that transmits malaria. A partial genomic library of An. maculatus, consisting of 3,960 kilobases (kb), was screened with either (GT)12 or (CT)12 probes. Approximately 1.5% of the recombinants contained sequences that hybridized to either (GT)12 or (CT)12 dinucleotide probes, suggesting that microsatellites are abundant in the genome of An. maculatus. Estimation of abundance of the two dinucleotide repeats revealed that (GT)n or (CA)n microsatellites occur on average every 68 kb and (CT)n or (GA)n repeats every 495 kb. Among 23 microsatellite loci sequenced, four loci were selected to synthesize primers to perform polymerase chain reaction scoring for genetic polymorphism in a population of An. maculatus. A high level of polymorphism was observed with all four microsatellite loci analyzed. The number of alleles detected at each locus ranged from eight to 12 and the heterozygosities ranged from 0.25 to 0.54. A total of 42 alleles were found among four microsatellite loci. The large number of alleles and polymorphic nature resolved from microsatellite loci make these markers valuable for the study of population genetic structure and gene flow. Knowledge of gene flow is required to develop vector control strategies using genetic manipulations of malaria vector populations.