Plasticity of the Worker Bumblebee Brain in Relation to Age and Rearing Environment

Abstract

The environment experienced during development can dramatically affect the brain, with possible implications for sensory processing, learning, and memory. Although the effects of single sensory modalities on brain development have been repeatedly explored, the additive or interactive effects of multiple modalities have been less thoroughly investigated. We asked how experience with multisensory stimuli affected brain development in the bumblebee Bombus impatiens. First, to establish the timeline of brain development during early adulthood, we estimated regional brain volumes across a range of ages. We discovered significant age-related volume changes in nearly every region of the brain. Next, to determine whether these changes were dependent upon certain environmental stimuli, we manipulated the visual and olfactory stimuli available to newly emerged bumblebee workers in a factorial manner. Newly emerged bumblebees were maintained in the presence or absence of supplemental visual and/or olfactory stimuli for 7 days, after which the volumes of several brain regions were estimated. We found that the volumes of the mushroom body lobes and calyces were larger in the absence of visual stimuli. Additionally, visual deprivation was associated with the expression of larger antennal lobes, the primary olfactory processing regions of the brain. In contrast, exposure to plant-derived olfactory stimuli did not have a significant effect on brain region volumes. This study is the first to explore the separate and interactive effects of visual and olfactory stimuli on bee brain development. Assessing the timing and sensitivity of brain development is a first step toward understanding how different rearing environments differentially affect regional brain volumes in this species. Our findings suggest that environmental factors experienced during the first week of adulthood can modify bumblebee brain development in many subtle ways.

Neuronal Plasticity in the Mushroom‐Body Calyx of Bumble Bee Workers During Early Adult Development

“…Most importantly, both parameters remain at a constant level after this initial change, suggesting that structural neuronal maturation during adult development is not only initiated but also completed at a very early stage in bumble bees. This coincides with the pattern found by Jones et al () in B. impatiens where calyx volume was shown to increase at a similar rate and data on B. occidentalis by Riveros and Gronenberg () who suggest an age‐related increase in MB volume exclusively within the first few days. Altogether, these findings indicate an exceptional position of bumble bees among social insects regarding their adult neuronal development.…”

Brain composition in Heliconius butterflies, posteclosion growth and experience‐dependent neuropil plasticity

“…Finally, it is also notable that plasticity, and particularly age‐related growth, is not restricted to the MB. Several visual and olfactory neuropils show age‐ and experience‐dependent expansions in Heliconius, as they do in other insects (Kühn‐Bühlmann and Wehner, ; Snell‐Rood et al, ; Ott and Rogers, ; Smith et al, ; Heinze and Florman, ; Jones et al, ). We also find evidence of plasticity in components of the CX.…”

Developmental exposure to pesticide contaminated food impedes bumblebee brain growth predisposing adults to become poorer learners

“…Furthermore, we found no consistent reduction in 289 volume of the optic lobes (medullas & lobulas) or central body for pesticide exposed workers. neuronal development and re-organisation therefore increases the risk of neurotoxic exposure interfering 298 with this process; iii) Our experimental setup was stimulus deprived and not void, therefore whilst 299 mushroom body volumetric increase is likely to be more experience independent than dependent, we 300 could not rule out investment in olfactory processing to compensate for a lack of visual information 301 (Fahrbach et al, 1998;Jones et al, 2013); iv) the change in growth of non-mushroom body neuropils was 302 simply too subtle for our μCT technology and/or sample sizes to detect. 303…”

“…Furthermore, the impact from brood exposure appeared irrecoverable despite no 22 exposure during adulthood. 23 2 24 1998; Jones et al, 2013;Maleszka et al, 2009;Riveros and Gronenberg, 2010). To distinguish the effects 65 of pesticide exposure from variation caused by other interacting factors, we therefore: i) attempted to 66 standardise experience and sensory input across tested workers, ii) tested workers of controlled age, and 67iii) compared between young and old age cohorts.…”