Abstract
Every year, millions of Australian Bogong moths (Agrotis infusa) complete an astonishing journey: In Spring, they migrate over 1,000 km from their breeding grounds to the alpine regions of the Snowy Mountains, where they endure the hot summer in the cool climate of alpine caves. In autumn, the moths return to their breeding grounds, where they mate, lay eggs and die. These moths can use visual cues in combination with the geomagnetic field to guide their flight, but how these cues are processed and integrated into the brain to drive migratory behavior is unknown. To generate an access point for functional studies, we provide a detailed description of the Bogong moth's brain. Based on immunohistochemical stainings against synapsin and serotonin (5HT), we describe the overall layout as well as the fine structure of all major neuropils, including the regions that have previously been implicated in compass-based navigation. The resulting average brain atlas consists of 3D reconstructions of 25 separate neuropils, comprising the most detailed account of a moth brain to date. Our results show that the Bogong moth brain follows the typical lepidopteran ground pattern, with no major specializations that can be attributed to their spectacular migratory lifestyle. These findings suggest that migratory behavior does not require widespread modifications of brain structure, but might be achievable via small adjustments of neural circuitry in key brain areas. Locating these subtle changes will be a challenging task for the future, for which our study provides an essential anatomical framework.
Highlights
One of the central questions in neuroscience is how animal behaviors result from neural computations
Our data allows the direct comparison of anatomical data from many individual brains, for instance data resulting from intracellular recordings combined with dye injections
The male standard brain is the average of 10 individual brains, generated by the iterative shape averaging (ISA) protocol, using the CMTK toolkit (Rohlfing et al, 2001)
Summary
One of the central questions in neuroscience is how animal behaviors result from neural computations. To delve deeper into this question, we need an animal model that shows a robust behavior and whose brain is accessible enough to allow for detailed physiological and genetic studies. Insects have long been reliable model organisms (Clarac and Pearlstein, 2007), as they have comparatively small brains that control a broad and remarkably complex behavioral repertoire. The moths return to their breeding grounds, mate, lay eggs and die. These seasonal migrations are similar to the migrations of the day-active Monarch butterfly in North America (Reppert et al, 2016), but unlike this species, which completes the migratory cycle over several generations, every Bogong moth completes the entire return journey (Common, 1954)
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