A well-documented phenomenon among social insects is that brain changes occur prior to or at the onset of certain experiences, potentially serving to prime the brain for specific tasks. This insight comes almost exclusively from studies considering developmental maturation in females. As a result, it is unclear whether age-related brain plasticity is consistent across sexes, and to what extent developmental patterns differ. Using confocal microscopy and volumetric analyses, we investigated age-related brain changes coinciding with sexual maturation in the males of the facultatively eusocial sweat bee, Megalopta genalis, and the obligately eusocial bumble bee, Bombus impatiens. We compared volumetric measurements between newly eclosed and reproductively mature males kept isolated in the lab. We found expansion of the mushroom bodies—brain regions associated with learning and memory—with maturation, which were consistent across both species. This age-related plasticity may, therefore, play a functionally-relevant role in preparing male bees for mating, and suggests that developmentally-driven neural restructuring can occur in males, even in species where it is absent in females.

We conducted this study in on Barro Colorado Island (BCI), Republic of Panama from March to May 2015 (Megalopta genalis) and at Utah State University, UT, USA from August to December 2018 (Bombus impatiens). For M. genalis newly eclosed (NE; < 24-h old) males from their natal nests, consisting of dead sticks or branches. For B. impatiens NE males were generated from microcolonies containing 5 workers (all from the same source colony). For both species, NE males were designated to one of two treatment groups: 1) newly-emerged (NE) or 2) lab-reared bees. NE males were sacrificed immediately (< 24-h old), whereas lab-reared males were housed individually in the laboratory for 6 d (M. genalis) or 10 d (B. impatiens). Laboratory rearing duration was determined based on the expected reproductive maturity of males within the species.

The deposited datasets include raw volumetric measurements from separate brain regions. These volumes were obtained using autofluorescence-based confocal microscopy (Zeiss LMS 710, Jena, Germany) on whole-brain mounts to generate image stacks for all samples. Each structure and the whole brain were traced individually on each slice of the confocal stack. We conducted unilateral traces (i.e., structure either on the left or right side of the brain) in 10 µm intervals. Volumetric measurements were generated using serial reconstruction.

ReadMe Files are included.