Abstract
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.
Highlights
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
Bombus impatiens N:K ratios were significantly higher in mature males than in newly eclosed males (Fig. 2b; t = − 5.12, df = 16, p = 0.0001, Hedges’ g = 2.48)
Results for calyx volume were similar when normalized to Kenyon cell volume instead of whole brain, such that the calyces were larger in mature males in both species, and mushroom body lobes were significantly enlarged in mature B. impatiens males when normalized to Kenyon cell volume
Summary
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. 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, 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. In the obligately eusocial bumble bee Bombus impatiens (Apidae), males mate only with reproductive gynes and not the abundant workers present among large c olonies[27] In both species, males remain in the nest for at least a few days following eclosion, and eventually leave or are ejected, presumably as they become reproductively mature[27,28]. If neuroplasticity coincides with reproductive maturation, mushroom bodies should expand with age, independent of experience
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