Population genetic analysis of Aedes aegypti reveals evidence of emerging admixture populations in coastal Kenya.

Background: The Aedes aegypti mosquito is widespread in tropical and subtropical regions. There are two recognized subspecies; the invasive Aedes aegypti aegypti (Aaa) and the ancestral Aedes aegypti formosus (Aaf). Aaf is common throughout Kenya whereas Aaa, which was historically confined to coastal regions, has undergone a range expansion. In areas of sympatry, gene flow may lead to admixed populations with potential differences in vectorial capacity. We hypothesize that coastal Ae. aegypti populations have a higher proportion of Aaa ancestry than those from inland locations of Kenya, influenced by their distance to the coast. Methodology: Adult Ae. aegypti mosquitoes were collected using Biogent (BG) sentinel traps baited with carbon-dioxide (CO2) from cities and towns along the Kenyan northern transport corridor. Aedes aegypti population structure, genetic diversity, and isolation by distance were analyzed using genome-wide single nucleotide polymorphism (SNPs) datasets generated with an Ae. aegypti microarray chip targeting ≈50,000 SNPs. Kenyan Aedes aegypti populations were placed into a global context within a phylogenetic tree, by combining the Kenyan dataset with a previously published global database database. Results: A total of a total of 67 Ae. aegypti mosquitoes population from Kenya were genotyped, we found that western Kenya Ae. aegypti constitute a genetically homogenous population that clusters with African Aaf, whereas coastal mosquitoes showed evidence of admixture between the two subspecies. There was a positive correlation (Observation = 0.869, p = 0.0023) between genetic distance (FST) and geographic distance, suggesting isolation by distance. The phylogenetic analysis and the genetic structure analysis suggest that an Asian Aaa population is the source of Aaa invasion into Kenya. Conclusions: These results provide evidence of the emerging an admixed population of Ae. aegypti in coastal Kenya between the sylvatic Aaf and the domesticated-human preferring Aaa. The observed gene flow from Aaa into Kenya may positively influence Ae. aegypti vectorial capacity, potentially increasing human feeding preference, biting rates and vector competence and could be promoting the observed dengue and chikungunya outbreaks. Author's summary: Aedes aegypti is of great public health concern due the viruses they transmit. The vector is highly invasive and is expanding to new geographic regions, quickly adaptiting to new environment. This study focuses in understanding the genetic structure of Ae. aegypti in cities along the northern transport corridor in Kenya, which are at risk of vector invasion. We analyzed Ae. aegypti populations using a panel of Single Nucleotide Polymorphism (SNPs) markers distributed across the genome. Our analysis show admixture in the coastal region between Aaf and Aaa, with Asian mosquitos being the putative source of Aaa ancestry, while the western populations are more related to African Aaf. This research provides a broad picture of the nature and dynamics of the Ae. aegypti populations across Kenya and sets the bases for further genetic studies focused on improving vector control strategies and developing novel mosquito control methods. [ABSTRACT FROM AUTHOR]

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