Molecular evolution of octopamine receptors in Drosophila

Abstract

Octopamine (OA), the insect analog of noradrenaline, plays important roles in diverse behavioral and physiological processes, from modulating fight-or-flight behavior to regulating post-mating ovulation. In Drosophila, six OA receptors have been identified: Oamb, Oct2R, Oct{beta}1R, Oct{beta}2R, Oct{beta}3R, and Oct-TyrR, and they have been linked to different behavioral and physiological processes. Here, we investigated the evolutionary characteristics of these receptors across Drosophila species. We found that OA receptors are generally found as single-copy genes. Notably, Oct{beta}2R and Oct{beta}3R exhibit positive selection within the melanogaster group, though in different structural regions from one another. The positively selected sites in Oct{beta}2R are exclusively located in regions important for ligand binding, whereas those in Oct{beta}3R are predominantly found in regions crucial for signal transduction. Interestingly, Oct{beta}2R remains highly conserved outside the melanogaster group, so the detection of positive selection in its ligand-binding related domains within this clade raises the possibility that it has evolved an additional, melanogaster-specific ligand interaction(s), among other potential reasons. These findings highlight the evolutionary flexibility of aminergic signaling and suggest lineage-specific adaptations of OA receptor function in Drosophila, likely shaped by lineage-specific selective pressures. Article summaryOctopamine is a chemical messenger in insects, analogous to noradrenaline in vertebrates, and influences many processes such as fight-or-flight responses, locomotion, and reproduction. In fruit flies and other insects, multiple octopamine receptors detect and respond to this signal. We explored how these receptors have changed over millions of years across various fly species. We found that while some receptors remain similar, others have evolved more rapidly, possibly due to changes in the insects lifestyles, environments, or other biological demands. Understanding these differences can help reveal how insects fine-tune their behaviors and adapt to diverse challenges.