Open Access Research

Ecological and genetic relationships of the Forest-M form among chromosomal and molecular forms of the malaria vector Anopheles gambiae sensu stricto

Yoosook Lee1*, Anthony J Cornel2, Claudio R Meneses1, Abdrahamane Fofana3, Aurélie G Andrianarivo1, Rory D McAbee2, Etienne Fondjo4, Sekou F Traoré3 and Gregory C Lanzaro1

Author Affiliations

1 School of Veterinary Medicine, Department of Pathology, Microbiology and Immunology, University of California – Davis, Davis, CA, USA

2 Department of Entomology, University of California – Davis, Davis, CA, USA

3 Malaria Research and Training Center, Faculty of Medicine, University of Mali, Bamako, Mali

4 National Malaria Program, Ministry of Health, Yaoundé, Cameroon

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Malaria Journal 2009, 8:75  doi:10.1186/1475-2875-8-75

Published: 21 April 2009

Abstract

Background

Anopheles gambiae sensu stricto, one of the principal vectors of malaria, has been divided into two subspecific groups, known as the M and S molecular forms. Recent studies suggest that the M form found in Cameroon is genetically distinct from the M form found in Mali and elsewhere in West Africa, suggesting further subdivision within that form.

Methods

Chromosomal, microsatellite and geographic/ecological evidence are synthesized to identify sources of genetic polymorphism among chromosomal and molecular forms of the malaria vector Anopheles gambiae s.s.

Results

Cytogenetically the Forest M form is characterized as carrying the standard chromosome arrangement for six major chromosomal inversions, namely 2La, 2Rj, 2Rb, 2Rc, 2Rd, and 2Ru. Bayesian clustering analysis based on molecular form and chromosome inversion polymorphisms as well as microsatellites describe the Forest M form as a distinct population relative to the West African M form (Mopti-M form) and the S form. The Forest-M form was the most highly diverged of the An. gambiae s.s. groups based on microsatellite markers. The prevalence of the Forest M form was highly correlated with precipitation, suggesting that this form prefers much wetter environments than the Mopti-M form.

Conclusion

Chromosome inversions, microsatellite allele frequencies and habitat preference all indicate that the Forest M form of An. gambiae is genetically distinct from the other recognized forms within the taxon Anopheles gambiae sensu stricto. Since this study covers limited regions of Cameroon, the possibility of gene flow between the Forest-M form and Mopti-M form cannot be rejected. However, association studies of important phenotypes, such as insecticide resistance and refractoriness against malaria parasites, should take into consideration this complex population structure.