Abstract
The M and S molecular forms of Anopheles gambiae s.s. have been considered incipient species for more than ten years, yet the mechanism underlying assortative mating of these incipient species has remained elusive. The discovery of the importance of harmonic convergence of wing beat frequency in mosquito mating and its relation to wing size have laid the foundation for exploring phenotypic divergence in wing size of wild populations of the two forms. In this study, wings from field collected mosquitoes were measured for wing length and wing width from two parts of the sympatric distribution, which differ with respect to the strength of assortative mating. In Mali, where assortative mating is strong, as evidenced by low rates of hybridization, mean wing lengths and wing widths were significantly larger than those from Guinea-Bissau. In addition, mean wing widths in Mali were significantly different between molecular forms. In Guinea-Bissau, assortative mating appears comparatively reduced and wing lengths and widths did not differ significantly between molecular forms. The data presented in this study support the hypothesis that wing beat frequency may mediate assortative mating in the incipient species of A. gambiae and represent the first documentation of a morphological difference between the M and S molecular forms.
Highlights
As one of the most important vectors of Plasmodium falciparum in west Africa, Anopheles gambiae s.s. has been the subject of great interest, with respect to speciation, population structure and gene flow
Mean wing size differed by both country and molecular form
As measured by wing width, appears to be a measurable phenotypic trait that may differentiate the molecular forms of A. gambiae s.s. in certain parts of its distribution
Summary
As one of the most important vectors of Plasmodium falciparum in west Africa, Anopheles gambiae s.s. has been the subject of great interest, with respect to speciation, population structure and gene flow. The two molecular forms: M and S, identified by a single nucleotide polymorphism in the ribosomal intergenic spacer [6,7], have been shown to have phenotypic divergence in different locations within their geographic range [8] that has led to their designation as incipient species. It has been proposed that the mechanism responsible for promoting divergence is prezygotic [13] and associated with mate selection either during swarm formation [14] or within a swarm [15]. One of the most difficult aspects to assess in these incipient species has been the mechanism responsible for assortative mating in wild populations. Acoustic information through the process of harmonic convergence has been suggested as a widespread mechanism for mate selection in mosquitoes [16]
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