Female olfactory sensitivity is temporally asynchronous with male courtship in a butterfly

Signal efficacy is crucial to communicative behaviors. To be effective, a signal once broadcast must be capable of being received and interpreted by a receiver or receivers. In addition to maximizing the amount that a signal stimulates receptive organs, the timing of when a signal is broadcast would optimally synchronize with a receiver's peak receptivity. Here, we investigated whether peak timing of male courtship, which includes release of a pheromone required for copulation to occur, is synchronized with female pheromone sensitivity in the butterfly Bicyclus anynana (Lepidoptera: Nymphalidae). To do this, we performed behavioral, pheromone, and electrophysiological assays at dawn, noon and dusk. We also investigated the diel rhythmicity of antennae gene expression by performing RNA sequencing on antennal tissues collected at the same three time points. We found that although males court most often near dusk and produce pheromones at constant levels throughout the day, females are more sensitive to odorants in the morning. Furthermore, female antennae exhibited differential and diurnally rhythmic expression of olfactory receptors and genes associated with learning and sexual receptivity, as well as gene ontology (GO) terms related to fatty acid metabolism and trehalose biosynthesis, supporting our diel electrophysiological results. Previous literature indicates that females form both positive and negative mate preference associations with male pheromones in the morning, regardless of whether males court females. Thus, this asynchrony may enable female B. anynana to learn mate preferences before they are courted by conspecific (or potentially heterospecific) males.