Bumblebee queens differ in brain morphology but not learning performance across life stages

Area of Science:

• Zoology
• Neuroscience
• Behavioral Ecology

Background:

• Animal cognition and brain morphology are influenced by social and ecological factors throughout an individual's life.
• Bumblebees face distinct ecological pressures depending on their life stage, such as foraging workers/gynes versus overwintering/reproductive queens.

Purpose of the Study:

• To compare visual learning and brain morphology in bumblebees (Bombus impatiens) across different social roles: workers, young queens (gynes), and reproductive queens.
• To investigate if foraging-stage gynes outperform reproductive queens in visual learning and if visual brain regions are reduced in reproductive queens, as seen in other social insects.

Main Methods:

• Behavioral assays measuring visual learning performance in age-matched workers, gynes, and reproductive queens.
• Comparative analysis of brain morphology, specifically focusing on visual (medulla, lobula) and olfactory (antennal lobes) regions.
• Examination of how brain region size scales with body size across different castes.

Main Results:

• Gynes and reproductive queens performed similarly in visual learning tasks, both outperforming workers.
• Reproductive queens possessed significantly larger olfactory regions (antennal lobes) compared to gynes.
• Visual brain regions (medulla and lobula) did not differ between gynes and reproductive queens.
• Brain regions exhibited different scaling relationships with body size between gynes and workers.

Conclusions:

• Social and ecological roles within a bumblebee colony significantly shape cognitive abilities and neural investment.
• Contrary to expectations based on other social insects, reproductive queens did not show reduced visual learning or smaller visual regions compared to gynes.
• The observed increase in olfactory regions in reproductive queens suggests a shift in sensory priorities associated with their reproductive stage and colony-founding responsibilities.