Standardization of the Compass Neuropils of the Australian Bogong Moth, Agrotis infusa

Abstract: Every summer the Australian Bogong moth migrates from southern Queensland to the Australian Alps in southern New South Wales. Other migrants such as the monarch butterfly use a time-compensated sun compass. However, the Bogong is nocturnal and only has access to skylight cues such as the moon, polarized light or the Milky Way. Since these are considerably unreliable only being visible short periods of time, another navigational mechanism could be a magnetic compass. In the Monarch the brain regions (neuropils) involved in navigation are the central complex, the lateral accessory lobes and the anterior optic tubercles; which together are called the ‘compass neuropils’. As the brain anatomy is the structural basis for all information processing underlying orientation and navigation, it can be used as an access point to understand this extraordinary migratory behaviour. We therefore performed 3D-reconstruction of the compass neuropils of the Bogong moth brain. By generating a standardized version of the compass neuropils I have created a common frame of reference for registration of neuron morphologies and networks, as well as providing reference volumes that were compared to those of the monarch. The Bogong moth brain was found to contain all the compass neuropils, however there was a significant difference between the two species neuropil-volumes. Interestingly, all components of the central complex were larger in the Bogong, while the upper unit of the anterior optic tubercle was substantially larger in the Monarch.