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Parallel evolution or purifying selection, not introgression, explains similarity in the pyrethroid detoxification linked GSTE4 of Anopheles gambiae and An. arabiensis

Wilding, CS and Weetman, D and Rippon, EJ and Steen, K and Mawejje, HD and Barsukov, I and Donnelly, MJ (2015) Parallel evolution or purifying selection, not introgression, explains similarity in the pyrethroid detoxification linked GSTE4 of Anopheles gambiae and An. arabiensis. MOLECULAR GENETICS AND GENOMICS, 290 (1). pp. 201-215. ISSN 1617-4615

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Abstract

Insecticide resistance is a major impediment to the control of vectors and pests of public health importance and is a strongly selected trait capable of rapid spread, sometimes even between closely-related species. Elucidating the mechanisms generating insecticide resistance in mosquito vectors of disease, and understanding the spread of resistance within and between populations and species are vital for the development of robust resistance management strategies. Here we studied the mechanisms of resistance in two sympatric members of the Anopheles gambiae species complex – the major vector of malaria in sub-Saharan Africa – in order to understand how resistance has developed and spread in eastern Uganda, a region with some of the highest levels of malaria.

In eastern Uganda, where the mosquitoes Anopheles arabiensis and An. gambiae can be found sympatrically, low levels of hybrids (0.4%) occur, offering a route for introgression of adaptively important variants between species. In independent microarray studies of insecticide resistance, Gste4, an insect-specific glutathione S-transferase, was among the most significantly up-regulated genes in both species. To test the hypothesis of interspecific introgression, we sequenced 2.3kbp encompassing Gste4. Whilst this detailed sequencing ruled out introgression, we detected strong positive selection acting on Gste4. However, these sequences, followed by haplotype-specific qPCR, showed that the apparent up-regulation in An. arabiensis is a result of allelic variation across the microarray probe binding sites which artefactually elevates the gene expression signal. Thus, facevalue acceptance of microarray data can be misleading and it is advisable to conduct a more detailed investigation of the causes and nature of such signal. The identification of positive selection acting on this locus led us to functionally express and characterise allelic variants of GSTE4. Although the in vitro data do not support a direct role for GSTE4 in metabolism, they do support a role for this enzyme in insecticide sequestration. Thus, the demonstration of a role for an up-regulated gene in metabolic resistance to insecticides should not be limited to simply whether it can metabolise insecticide; such a strict criterion would argue against the involvement of GSTE4 despite the weight of evidence to the contrary.

Item Type: Article
Additional Information: The final publication is available at Springer via http://dx.doi.org/10.1007/s00438-014-0910-9
Uncontrolled Keywords: 0604 Genetics
Subjects: Q Science > QH Natural history > QH301 Biology
Q Science > QL Zoology
Divisions: Natural Sciences and Psychology
Publisher: SPRINGER HEIDELBERG
Related URLs:
Date Deposited: 18 Jan 2016 10:14
Last Modified: 08 Sep 2017 00:10
DOI or Identification number: 10.1007/s00438-014-0910-9
URI: http://researchonline.ljmu.ac.uk/id/eprint/2636

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