Ecological plasticity to ions concentration determines genetic response and dominance of Anopheles coluzzii larvae in urban coastal habitats of Central Africa

Abstract

In Central Africa, the malaria vector Anopheles coluzzii is predominant in urban and coastal habitats. However, little is known about the environmental factors that may be involved in this process. Here, we performed an analysis of 28 physicochemical characteristics of 59 breeding sites across 5 urban and rural sites in coastal areas of Central Africa. We then modelled the relative frequency of An. coluzzii larvae to these physicochemical parameters in order to investigate environmental patterns. Then, we assessed the expression variation of 10 candidate genes in An. coluzzii, previously incriminated with insecticide resistance and osmoregulation in urban settings. Our results confirmed the ecological plasticity of An. coluzzii larvae to breed in a large range of aquatic conditions and its predominance in breeding sites rich in ions. Gene expression patterns were comparable between urban and rural habitats, suggesting a broad response to ions concentrations of whatever origin. Altogether, An. coluzzii exhibits a plastic response to occupy both coastal and urban habitats. This entails important consequences for malaria control in the context of the rapid urban expansion in Africa in the coming years.

Figure 1

Regional distribution of An. coluzzii and An. gambiae in the collection sites.

Figure 2

Breeding sites characterization according to the physico-chemical variables. (A) Principal components selected with the Broken Stick model. (B) Canonical weight of each variable on the principal components; the arrow size indicates the importance of the parameter. (C) and (D) PCA diagrams showing the correlations between rural and urban breeding sites and physicochemical characteristics.

Figure 3

Association between environment type and altitude and An. coluzzii frequency.

Figure 4

Correlation between gene expression profiles, habitat (rural and urban) and environmental predictors. (A) Association between habitat type and expression for each gene. (B) Coinertia diagram between gene expression on the left, and environmental predictors on the right. (C) Correlogram between genes (“number” = correlation coefficients; significance code 0’***’, 0.001'**', 0.01'*', 0.05'.' and 0.1' '; each blue cross (*) corresponds to a site).