The adaptive benefits of adult structural plasticity in the mushroom bodies of freely behaving forager honey bees

The mushroom bodies (MBs) are insect brain regions associated with sensory integration and learning. The dendrites of the intrinsic MB neurons (the Kenyon cells) are in the calycal neuropil, where they receive input from primary sensory neuropils. The calyces are larger in older forager honey bees than in younger non-foragers. Additionally, the microglomeruli in the MB calyces reorganize with age such that older individuals have fewer but larger microglomeruli than younger individuals. It is suggested that such changes in MB organization support learning of complicated foraging tasks. Prior studies focused on the experiences that promote MB growth and the cellular processes that cause this growth; however, the consequences of MB growth for an individual have never been examined. Experience clearly fine-tunes brain structure in animals, but how does this feed forward onto behavior? We developed a field-based visual-discrimination task that mimics aspects of natural foraging. Foragers learned to associate the hue of an artificial flower with a sucrose reward. Each forager was monitored over 12 visits to the flower patch and scored on the rate at which the association was learned. This task revealed three behavioral cohorts: 30% of foragers learned the association in fewer than 6 visits (Category 1), 30% of foragers learned the association in 6 or more visits (Category 2), and 40% of foragers did not learn the association within the 12 allowed visits (Category 3). Learning scores were correlated with microglomerular organization in the MB calyces via whole-brain immunolabeling and confocal microscopy. While our age-based results closely match those of previous studies, we found no differences in the volume of individual microglomeruli or the density of microglomeruli (number of microglomeruli per unit volume of MB calyx) using standard statistical analyses between the most extreme behavioral cohorts (Category 1 and Category 3). New statistical approaches using randomization tests on distributions of microglomerular volume suggest that the structural differences between the Category 1 and Category 3 brains are very subtle. Microglomerular volume and density changes have been reported to vary with overall MB calycal volume, however the subtle differences we found have never been examined before.

Grantor dc:publisher

Wake Forest University

Year dc:date.issued

2016

Author dc:creator

• Van Nest, Byron N.

• Apis mellifera

Language dc:language.iso

en

Handle dc:identifier.uri

http://hdl.handle.net/10339/59282

OAI identifier oai:identifier

oai:wakespace.lib.wfu.edu:10339/59282