Abstract
BackgroundUnderstanding population genetic structure in the malaria vector Anopheles gambiae (s.s.) is crucial to inform genetic control and manage insecticide resistance. Unfortunately, species characteristics such as high nucleotide diversity, large effective population size, recent range expansion, and high dispersal ability complicate the inference of genetic structure across its range in sub-Saharan Africa. The ocean, along with the Great Rift Valley, is one of the few recognized barriers to gene flow in this species, but the effect of inland lakes, which could be useful sites for initial testing of genetic control strategies, is relatively understudied. Here we examine Lake Victoria as a barrier between the Ugandan mainland and the Ssese Islands, which lie up to 60 km offshore. We use mitochondrial DNA (mtDNA) from populations sampled in 2002, 2012 and 2015, and perform Bayesian cluster analysis on mtDNA combined with microsatellite data previously generated from the same 2002 mosquito DNA samples.ResultsHierarchical analysis of molecular variance and Bayesian clustering support significant differentiation between the mainland and lacustrine islands. In an mtDNA haplotype network constructed from this and previous data, haplotypes are shared even between localities separated by the Rift Valley, a result that more likely reflects retention of shared ancestral polymorphism than contemporary gene flow.ConclusionsThe relative genetic isolation of An. gambiae on the Ssese Islands, their small size, level terrain and ease of access from the mainland, the relative simplicity of the vectorial system, and the prevalence of malaria, are all attributes that recommend these islands as possible sites for the testing of genetic control strategies.
Highlights
Understanding population genetic structure in the malaria vector Anopheles gambiae (s.s.) is crucial to inform genetic control and manage insecticide resistance
Few physical barriers to An. gambiae dispersal are known across continental Africa and very shallow spatial population genetic structure exists continent-wide, with the notable exception of populations separated by the Rift Valley [9, 13,14,15,16,17]
Using either whole protein-coding mitogenomes or a relatively small fragment of the mitochondrial DNA (mtDNA) nad5 gene, we obtained evidence consistent with restricted connectivity between the Ssese Islands in Lake Victoria and the Ugandan mainland, despite the fact that the islands sampled were within 60 km of the mainland
Summary
Understanding population genetic structure in the malaria vector Anopheles gambiae (s.s.) is crucial to inform genetic control and manage insecticide resistance Species characteristics such as high nucleotide diversity, large effective population size, recent range expansion, and high dispersal ability complicate the inference of genetic structure across its range in sub-Saharan Africa. Anopheles gambiae (s.s.) (formerly An. gambiae S-form) is a principal vector of malaria in sub-Saharan Africa, where 91% of an estimated 445,000 malaria deaths worldwide occurred in 2016 [1] This species is distributed broadly across most of tropical Africa, including its offshore islands, occupying a diversity of ecological settings but almost invariably in association with rural or peri-urban human populations [2,3,4]. The magnitude of genetic differentiation (FST) between populations on opposite sides of the continent (~6,000 km apart) is ~0.03, while the corresponding value between populations on either side of the Rift Valley (~400–500 km) is ~0.1 [14,15,16,17]
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