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Abstract
BackgroundOlfaction plays a significant role in insect behavior during critical steps of their life-cycle, such as host-seeking during foraging or the search for a mate. Here, we explored genetic polymorphism within and divergence between sibling species of the African malaria mosquito, Anopheles gambiae sensu lato in the gene sequence and encoded peptides of an odorant receptor, Or39. This study included sympatric specimens of An. gambiae sensu stricto, An. coluzzii and An. arabiensis sampled together in the village of Dielmo, Senegal.ResultsA 1,601 bp genomic sequence composed of 6 exons and 5 introns was obtained for Or39 from 6–8 mosquitoes in each of the 3 species. DNA sequence analysis revealed a high level of molecular polymorphism (π = 0.0154; Haplotype diversity = 0.867) and high overall genetic differentiation between taxa (Fst > 0.92, P < 0.01). In total, 50 parsimony informative sites were recorded. Throughout the whole dataset, there were 13 non-synonymous mutations resulting in aminoacid changes in the encoded protein. Each of the 6 different identified peptides was species-specific and none was shared across species. Most aminoacid changes were located on the intracellular domains of the protein. However, intraspecific polymorphisms in An. gambiae and An. arabiensis as well as species-specific mutations also occurred in the first extracellular domain.ConclusionsAlthough obtained from a limited number of specimens, our results point towards genetic differences between cryptic species within the An. gambiae complex in a gene of biological relevance that might be of evolutionary significance when exposed to disruptive selective forces.
Highlights
Olfaction plays a significant role in insect behavior during critical steps of their life-cycle, such as host-seeking during foraging or the search for a mate
We provide new data on Or39 molecular polymorphism by i) expanding the breadth of the sequencing effort to cover a larger portion of the gene, including 6 exons and 5 introns, and ii) exploring molecular polymorphism and divergence in this gene among specimens of An. gambiae, An. coluzzii and An. arabiensis collected in Senegal (West Africa), a geographic area where the 3 species co-exist and where genetic admixture between An. gambiae and An. coluzzii has been reported [11,25,26]
A 1,608-bp DNA sequence was obtained for the entire Or39 gene from 7 An. gambiae and 6 An. coluzzii specimens
Summary
Olfaction plays a significant role in insect behavior during critical steps of their life-cycle, such as host-seeking during foraging or the search for a mate. The Anopheles gambiae sensu lato complex groups together 8 sibling species, including 2 of the most powerful African human malaria vectors, An. arabiensis (Patton, 1905) and An. gambiae sensu stricto (Gile, 1902). The latter comprises 2 incipient species named An. gambiae (formerly, An. gambiae S form) and An. coluzzii (formerly, An. gambiae M form) which are genetically and studies using the previous molecular forms’ nomenclature have shown that swarming and mating mainly involved mosquitoes of the same form [13,14,15] and that males and females engage in close-range acoustic interactions by shifting their flight tones to match each other prior to copulation [16]. Different populations of the 2 incipient species are known to exhibit different levels of reproductive isolation in different geographic locations across their range [10,11,25]
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