Dynamics of gene introgression in the African malaria vector Anopheles gambiae

Abstract

Anopheles gambiae is a major malaria vector in Africa and a popular model species for a variety of ecological, evolutionary, and genetic studies on vector control. Genetic manipulation of mosquito vectorial capacity is a promising new weapon for the control of malaria. However, the release of exotic transgenic mosquitoes will bring in novel alleles in addition to the parasite-inhibiting genes, which may have unknown effects on the local population. Therefore, it is necessary to develop methodologies that can be used to evaluate the spread rate of introduced genes in A. gambiae. In this study, the effects and dynamics of genetic introgression between two geographically distinct A. gambiae populations from western Kenya (Mbita) and eastern Tanzania (Ifakara) were investigated with amplified fragment length polymorphisms (AFLPs) and microsatellite markers. Microsatellites and polymorphic cDNA markers revealed a large genetic differentiation between the two populations (average F(ST) = 0.093, P < 0.001). When the two strains were crossed in random mating between the two populations, significant differences in the rate of genetic introgression were found in the mixed populations. Allele frequencies of 18 AFLP markers (64.3%) for Mbita and of 26 markers (92.9%) for Ifakara varied significantly from F5 to F20. This study provides basic information on how a mosquito release program would alter the genetic makeup of natural populations, which is critical for pilot field testing and ecological risk evaluation of transgenic mosquitoes.

Figure 1.

AFLP allele frequency change patterns in the mixed population of the Ifakara and Mbita strains of Anopheles gambiae. Solid markers represent significantly higher allele frequency than that of the Mbita parent strain, and hatched markers are those with significantly lower frequencies at P < 0.001 after a sequential Bonferroni correction. Shaded markers show no significant change in allele frequencies from that of the Mbita parent strain. An asterisk (*) indicates markers with alleles specific to one parent strain. Microsatellite markers (names beginning with AG) are used as anchors for AFLP marker orientation. AFLP markers are designated by the EcoRI primer name, the MseI primer name, and the molecular size of the fragment. For example, marker L7A27.133 represents the 133-bp fragment amplified by EcoRI primer L7 and MseI primer A27, whereas L1A10.266 represents the 266-bp fragment amplified by EcoRI primer L1 and MseI primer A10.