Evolution of Expression Pattern of the Olfactory Receptor Or103 in Aedes aegypti

Abstract

Aedes aegypti is a noteworthy example of a species that has specialized on humans. While the ancestral forest form prefers non-human animals, the derived domestic form prefers to feed on humans. Changes in the olfactory system probably play an important role in this shift, as it is what mosquitoes rely on to identify human hosts. Or103 is one of a couple of olfactory receptors that seem to be key players in the evolution of preference for humans. Interestingly, recent work has shown that the projection pattern of Or103 neurons does not follow the canonical one-receptor-one-glomerulus organization delineated in other insect olfactory systems; visualization of the antennal lobe of domestic females has shown an unusual pattern of three Or103-positive glomeruli. In this study, I visualized the projection pattern of Or103 neurons in forest mosquitoes. The aim was to investigate the differences between domestic and forest mosquitoes and determine whether the three-glomerulus pattern is a recent evolutionary change associated with preference, or whether it is conserved in ancestral forest strains. I found that Or103 neurons project to one glomerulus in forest females, indicating that its pattern of expression has evolved. Though there remains much speculation regarding the role of Or103 in host preference, this study supports the hypothesis that the increased expression of Or103 in domestic mosquitoes drives human preference.