Multiple Origins of Knockdown Resistance Mutations in the Afrotropical Mosquito Vector Anopheles gambiae

João Pinto,Nadine P Randle,Martin J Donnelly,Federica Santolamazza,José L Vicente,Jacques Derek Charlwood,Marta Moreno,Alessandra Della Torre,Adalgisa Caccone,Amy Lynd,Gabriele Gentile,Virgílio E Do Rosário,Frédéric Simard,Niyaz Ahmed

doi:10.1371/journal.pone.0001243

Abstract

How often insecticide resistance mutations arise in natural insect populations is a fundamental question for understanding the evolution of resistance and also for modeling its spread. Moreover, the development of resistance is regarded as a favored model to study the molecular evolution of adaptive traits. In the malaria vector Anopheles gambiae two point mutations (L1014F and L1014S) in the voltage-gated sodium channel gene, that confer knockdown resistance (kdr) to DDT and pyrethroid insecticides, have been described. In order to determine whether resistance alleles result from single or multiple mutation events, genotyping of the kdr locus and partial sequencing of the upstream intron-1 was performed on a total of 288 A. gambiae S-form collected from 28 localities in 15 countries. Knockdown resistance alleles were found to be widespread in West Africa with co-occurrence of both 1014S and 1014F in West-Central localities. Differences in intron-1 haplotype composition suggest that kdr alleles may have arisen from at least four independent mutation events. Neutrality tests provided evidence for a selective sweep acting on this genomic region, particularly in West Africa. The frequency and distribution of these kdr haplotypes varied geographically, being influenced by an interplay between different mutational occurrences, gene flow and local selection. This has important practical implications for the management and sustainability of malaria vector control programs.

Highlights

The development of insecticide resistance is regarded as a favored empirical model to study the molecular evolution of adaptive traits
Knockdown resistance associated alleles were not homogeneously present in the samples analysed (Figure 1; Table S1): i) in Western African samples (2N = 202 sequences), from Nigeria to Senegal, the L1014F was the only mutation found; ii) in the West-Central region of Africa (2N = 254), comprising Angola, Gabon, Equatorial Guinea and Cameroon, both kdr alleles co-occurred in 8 localities surveyed
Analysis of the upstream intron-1 of the kdr locus suggests at least four independent origins of kdr alleles in the principal Afrotropical malaria vector A. gambiae S-form

Summary

Introduction

The development of insecticide resistance is regarded as a favored empirical model to study the molecular evolution of adaptive traits. The resistance phenotype is usually associated with a few major genes or gene classes and mutations therein that confer the trait [1]. Within this framework, particular attention has been given to determining how often resistance mutations arise in natural populations. Multiple origins of resistance alleles involving different genes have been documented in several insect species These include point mutations at the voltage-gated sodium channel gene of Bemisia tabaci and Myzus persicae [4,5], c-aminobutyric acid (GABA) receptors in Tribolium castaneum [6] and esterase genes in Lucilia cuprina [1]

Methods

Results

Conclusion