Sex-Specific Neuroplasticity in the Brain of a Facultatively Social Orchid Bee.

Neuroplasticity enables the brain to reorganize in response to developmental change and experience, thereby supporting behavioral flexibility. In insects, both age and experience are known to influence neural structure, but how these factors differ between the sexes remains largely unexplored. Here, using micro-CT scanning, we quantify volumetric plasticity across eight brain regions in the orchid bee Euglossa dilemma, a facultatively social species with pronounced sexual dimorphism in behavior. We show that neuroplasticity follows sex- and region-specific trajectories that map onto the distinct reproductive behaviors exhibited by male and female bees. Consistent with other insect species, both sexes exhibited neuroplasticity in the mushroom bodies but only males showed an experience-dependent expansion, which we attribute to the navigational demands of reproductive behaviors. This was further supported by the expansion of olfactory and visual processing centers associated with the sensory demands of perfume collection and courtship display. Females, in contrast, undergo an exclusively age-dependent volumetric expansion of the mushroom bodies, an experience-dependent expansion of the antennal lobes, and a reduction of the visual neuropils. These patterns of plasticity correlate with female nesting behavior and may reveal potential energy trade-offs during reproduction. Our findings provide the first evidence of exclusively age-driven neuroplasticity in the mushroom bodies of social female bees and establish E. dilemma as a valuable comparative model for studying the evolution of brain plasticity and behavioral adaptation in social insects.