226 - Introgression and adaptation in Aedes aegypti mosquitoes from Saudi Arabia

Abstract: Introgression between genetically distinct populations can introduce adaptive alleles and facilitate invasion of new habitats. Five thousand years ago, the sylvatic generalist subspecies of Aedes aegypti, the yellow fever mosquito, began a domestication process when water became scarce during the Sahara Desert expansion, culminating ~220 years ago with the evolution of the highly invasive-domesticated subspecies that later spread around the world as the arbovirus vector of excellence. Admixture between the subspecies has only been reported in a few locations of the coast of Africa and in Saudi Arabia, where populations span diverse ecological regions. Understanding the genetic structure and adaptive potential of this species is critical for vector management. This study investigates the role of genetic introgression from African Ae. aegypti into Saudi Arabian populations, particularly in the southern and western regions, using a panel of 13,455 genome-wide polymorphic sites. Genomic analyses reveal pronounced genetic differentiation between western and southern populations, with Jazan Highland (southern) displaying the highest proportion of African ancestry. Admixture and phylogenetic analyses indicate multiple migratory pulses into southern Saudi Arabia, suggesting that African populations act as a reservoir of adaptive genetic variation. Selection scans on Saudi Ae. aegypti highlight genomic regions associated with metabolic pathways, protein processing, and cellular stress responses, aligning with water availability across Saudi Arabia regions. This study identifies a set of alleles across multiple loci with potential role in drought tolerance, providing a basis for further investigation into the evolutionary processes shaping Ae. aegypti adaptation to arid regions. This research highlights the role of secondary contact and hybridization between genetically distinct populations in local environmental adaptation and potential implications for vector control strategies. Future research should explore the functional roles of these adaptive genes to better understand their impact on the ecology and epidemiology of Ae. aegypti.