Ecological genetic studies in the chromosomal form Mopti ofAnopheles gambiae s.str. in Mali, West Africa

Abstract

Among the sibling species of the Afrotropical Anopheles gambiae complex, the nominal taxon (An. gambiae s.str.) is the major malaria vector. Its bionomics suggest a man-dependent speciation process which involves, in West Africa, various incipient species chromosomally recognized by different combinations of 2R paracentric inversions. One of the most recent evolutionary steps of such a speciation process appears to be the chromosomal form Mopti, which is associated with dry season irrigation in arid zones, and is characterized by a remarkable ecological flexibility related to three 2R alternative arrangements, namely bc, u and +, whose expected karyotypes are found in Hardy-Weinberg equilibrium. The study of this chromosomal polymorphism in samples from a 16-locality transect in Mali shows wide variations and highly significant correlation with both temporal and spatial climatic differences. Mosquitoes homokaryotypic for 2Rbc are the actual dry season and arid areas breeders. The regular rise of 2Rbc frequency, up to fixation, during each dry season, corresponds to the South-North clinal increase of the same arrangement along the transect, from about 30% in the humid savanna to near fixation in the South-Saharan zone. This coherent ecological genetics case provides full support to the hypothesis of the adaptive nature of paracentric inversions. Moreover, the very peculiar system of combinations of contiguous 2R inversions, utilized by Mopti as well as by other chromosomal forms of An. gambiae, suggests a process of polygenic reorganization based on linkage disequilibria and involving the inversions as driving selection units.

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).…”

Population genetic structure of the malaria vector Anopheles minimus A in Vietnam

“…In West Africa different chromosomal forms of An. gambiae have been identified associated with ecoclimatological zones (Coluzzi, 1992;Toure et al, 1994;Powell et al, 1999). Yet, the taxonomic status of these chromosomal forms is still debated (Black and Lanzaro, 2001).…”

Comparative genomic analysis in the region of a major Plasmodium -refractoriness locus of Anopheles gambiae

“…Since this work was completed, a similar conclusion has been reached in the whole-genome sequencing effort (R. Holt, personal communication). A. gambiae (sensu strictu) has been distinguished into several different ecotypes on the basis of floating chromosomal inversions, whose prevalence varies geographically and seasonally, suggesting that they may ''lock in'' specific allelic combinations important for malaria transmission (35,36). More recently, a small number of molecular markers have also suggested the existence of flexibility and even mosaicism in the A. gambiae genome (37,38).…”