Butterfly brains change in morphology and in gene splicing patterns after brief pheromone exposure

How insect brains differ between the sexes and respond to sex-specific pheromones is still not well understood. Here we briefly exposed female Bicyclus anynana butterflies to wild type and modified male sex pheromone blends, previously shown to modify females' sexual preferences, and examined how their brains were modified at the morphological and molecular levels 3 days later. First, we 3D-reconstructed male and female brains of this species and explored changes in the size of the 67 glomeruli present in the olfactory lobe. Then we showed that one glomerulus changed in volume after a blend exposure, potentially implicating it in sex pheromone perception. Finally, we found that a few genes were differentially expressed but many more were differentially spliced between male and female naïve brains, and between naive and pheromone blend-exposed brains. These code for primarily calcium-binding channel proteins and RNA-binding proteins, respectively. A learned preference for changed levels in a single pheromone component was linked to different protein isoforms involved in synaptic transmission. Our work shows that naïve male and female brains differ primarily in gene splicing patterns and that a brief, 3-min, exposure to pheromones produces slight changes in brain volume and large changes in the splicing of genes involved in neural development, which correlate with changes in sexual preferences in females.