Complexities in the genetic structure of Anopheles gambiae populations in west Africa as revealed by microsatellite DNA analysis

Abstract

Chromosomal forms of Anopheles gambiae, given the informal designations Bamako, Mopti, and Savannah, have been recognized by the presence or absence of four paracentric inversions on chromosome 2. Studies of karyotype frequencies at sites where the forms occur in sympatry have led to the suggestion that these forms represent species. We conducted a study of the genetic structure of populations of An. gambiae from two villages in Mali, west Africa. Populations at each site were composed of the Bamako and Mopti forms and the sibling species, Anopheles arabiensis. Karyotypes were determined for each individual mosquito and genotypes at 21 microsatellite loci determined. A number of the microsatellites have been physically mapped to polytene chromosomes, making it possible to select loci based on their position relative to the inversions used to define forms. We found that the chromosomal forms differ at all loci on chromosome 2, but there were few differences for loci on other chromosomes. Geographic variation was small. Gene f low appears to vary among different regions within the genome, being lowest on chromosome 2, probably due to hitchhiking with the inversions. We conclude that the majority of observed genetic divergence between chromosomal forms can be explained by forces that need not involve reproductive isolation, although reproductive isolation is not ruled out. We found low levels of gene f low between the sibling species Anopheles gambiae and Anopheles arabiensis, similar to estimates based on observed frequencies of hybrid karyotypes in natural populations.

Revisiting the role of introgression vs shared ancestral polymorphisms as key processes shaping genetic diversity in the recently separated sibling species of the Anopheles gambiae complex

“…These data provide a corollary of the results of microsatellite-based macrogeographic studies of differentiation in both species Kamau et al, 1998;Lanzaro et al, 1998;Simard et al, 1999;Donnelly and Townson, 2000). In general, as in microsatellite-based studies the levels of population differentiation were lower in A. arabiensis (Figure 2) (Donnelly and Townson, 2000;Lehmann et al, 2003) and the only large estimates of F ST involved an island population which is likely to have experienced founding effects/ genetic bottleneck (Simard et al, 1999;Donnelly et al, 2002).…”

“…The data in this study also serve as additional markers to compare with the large number of microsatellite-based studies that have investigated population structuring in these organisms on micro-and macrogeographic scales Kamau et al, 1998;Lanzaro et al, 1998;Simard et al, 1999;Donnelly and Townson, 2000;Wondji et al, 2002).…”

Identification and characterization of microsatellite markers in the Chagas disease vector Triatoma dimidiata

“…Both extremes could be useful for future studies, depending on the goal of the study. The apparent excess of homozygotes at locus three could be due to a null allele, the lack of amplification on one chromosome, as a result of a mutation in the primer annealing site (Lanzaro et al, 1998). Conversely, the lack of homozygote 106/106 at locus 22 could simply be attributed to a small sample size collected from several sites distributed over a large geographic region.…”

The availability of potential hosts as a determinant of feeding behaviours and malaria transmission by African mosquito populations

“…These apparently large contrasts in host choice by An. gambiae in East and West Africa may result from between-site differences in innate behavioural traits of the vectors (Touré et al, 1994;Lanzaro et al, 1998;COETZEE et al, 2000), spatial relationships of hosts, vectors and larval habitats (Kitron & Spielman, 1989;Kitron, 1998), personal protection (Lindsay et al, 1989 or housing design (Gamage-Mendis et al, 1991;Ghebreyesus et al, 2000). Of these factors, the unusually longstanding and widespread use of bednets in The Gambia deserves particular attention because such domestic personal protection measures can discourage feeding on humans and reduce human blood indices (Garrett-Jones, 1964;Charlwood & Graves, 1987;Lindsay et al, 1989;Githeko et al, 1996a;Bøgh et al, 1998).…”