A tale of two copies: Evolutionary trajectories of moth pheromone receptors.

Abstract

Pheromone communication is an essential component of reproductive isolation in animals. As such, evolution of pheromone signaling can be linked to speciation. For example, the evolution of sex pheromones is thought to have played a major role in the diversification of moths. In the crop pests <i>Spodoptera littoralis</i> and <i>S. litura</i>, the major component of the sex pheromone blend is (<i>Z</i>,<i>E</i>)-9,11-tetradecadienyl acetate, which is lacking in other <i>Spodoptera</i> species. It indicates that a major shift occurred in their common ancestor. It has been shown recently in <i>S. littoralis</i> that this compound is detected with high specificity by an atypical pheromone receptor, named SlitOR5. Here, we studied its evolutionary history through functional characterization of receptors from different <i>Spodoptera</i> species. SlitOR5 orthologs in <i>S. exigua</i> and <i>S. frugiperda</i> exhibited a broad tuning to several pheromone compounds. We evidenced a duplication of OR5 in a common ancestor of <i>S. littoralis</i> and <i>S. litura</i> and found that in these two species, one duplicate is also broadly tuned while the other is specific to (<i>Z</i>,<i>E</i>)-9,11-tetradecadienyl acetate. By using ancestral gene resurrection, we confirmed that this narrow tuning evolved only in one of the two copies issued from the OR5 duplication. Finally, we identified eight amino acid positions in the binding pocket of these receptors whose evolution has been responsible for narrowing the response spectrum to a single ligand. The evolution of OR5 is a clear case of subfunctionalization that could have had a determinant impact in the speciation process in <i>Spodoptera</i> species.