Brain differences between social castes precede group formation in a primitively eusocial bee.

Area of Science:

• Neuroethology
• Insect social behavior
• Comparative neuroanatomy

Background:

• Social interactions significantly influence brain development.
• In primitively eusocial insects, the mushroom body (MB), crucial for sensory integration and learning, is larger in queens than workers.
• This size difference may stem from neural investment strategies or plastic responses to social environments.

Purpose of the Study:

• To investigate whether larger mushroom bodies in reproductives precede social group formation.
• To compare brain structures between solitary nest foundresses and workers in the primitively eusocial sweat bee Augochlorella aurata.

Main Methods:

• Comparative analysis of brain structure sizes.
• Measurement of whole brain size, mushroom body size, optic lobe size, and antennal lobe size in foundresses and workers.

Main Results:

• Nest foundresses possess significantly larger mushroom bodies (MBs) than workers.
• No significant differences were observed in whole brain size or optic lobe size.
• Foundresses also exhibit larger antennal lobes compared to workers.

Conclusions:

• Increased neural investment in mushroom bodies occurs before the establishment of social groups.
• Larger MBs in foundresses may be attributed to factors like enhanced larval nutrition and absence of social aggression.
• These findings provide insights into the developmental plasticity of the brain in response to social and nutritional factors in primitively eusocial insects.