Increased heterozygosity and balancing selection in isofemale generations of Anopheles stephensi under laboratory conditions

Abstract

Background - The urban malaria vector, Anopheles stephensi, originally limited to South Asia and the Arabian Peninsula has now expanded to several countries in Africa. Despite the continuous insecticide pressure and changing urban landscapes, An. stephensi has been able to adapt, sustain, and expand. The expansion of this remarkably sturdy vector poses a grave public health threat to millions in urban Africa. Research efforts across the globe have mainly focused on understanding the genes that support and limit the development of Plasmodium in An. stephensi. Understanding the genes that are critical for adaptation and survival is important for focused An. stephensi’s control and elimination efforts. Balancing selection is an evolutionary mechanism adapted by organisms to maintain genetic diversity, especially for immune-related genes. Here, we sequenced and analyzed the genome of laboratory-reared isofemale once every 25 th generation—0 (Wild type), 25 th, 50 th, 75 th, 100 th, 125 th, and 150 th to identify loci and genes undergoing balancing selection—information that could aid in vector control. Results- Tajima’s D and beta scores were used to identify the signatures of selection in the genomes of seven isofemale An. stephensi from 0 - 150 th generation. Based on the beta scores, the top five genes undergoing balancing selection include ASTEI04624, ASTEI04623 (sensory perception), ASTEI10474 (carbohydrate metabolism), ASTEI03792 (Actin binding), and ASTEI01081 (yet to be functionally characterized). Conclusion -For its survival, a certain amount of heterozygosity and balancing selection in specific loci, especially in genes involved in carbohydrate metabolism and chemoreception is maintained by the inbred laboratory-reared isofemale An. stephensi. This could be a functional adaptation to the glucose-based diet they are fed in the laboratory.