There and back again: The neural basis of migration in the Bogong moth

Research output: ThesisDoctoral Thesis (compilation)

Abstract

The Bogong moth (Agrotis infusa) is a small, night-active Australian moth that has a remarkable lifestyle. After
hatching from its pupa in spring, it migrates over 1000 km to the Australian Alps, where it spends the summer in
cool alpine caves. In the beginning of autumn, the moths emerge from the caves and fly back to their breeding
grounds, where they mate, lay eggs, and die. The following year, a new generation of moths repeats the same
journey to the mountains.
Migration is a difficult and dangerous task. If the moths get lost on the way, they will not arrive at the caves in time
and will instead perish in the hot Australian summer. It is therefore crucial that they are efficient and reliable
navigators. However, the brains of these moths are tiny – only 3 mm in diameter. How can such a small brain
compute the trajectory of this extraordinary migration?
In this thesis, I investigated the neural basis of navigation and migration in the Bogong moth. I began by describing
the Bogong moth brain in detail (Paper I). In insects, neurons in a brain region known as the central complex process
spatial information and provide the spatial context for behavioural decisions. The central complex of the Bogong
moth is well developed and can be expected to have the same function as in other insects. From previous studies,
we know that brain regions that are of special importance for an animal tend to be bigger. I therefore compared the
volume of several higher processing neuropils, including the central complex, across several moth species (Paper
II), including both migrants and non-migrants. I found that that the relative volumes of the central complex across
species were very similar. In fact, the central complex scaled hypo-isometrically, suggesting that the neural networks
in this brain region are so fundamentally important that even the smallest moths cannot afford to reduce them further.
Therefore, instead of being reflected in the overall volume of the central complex, migratory behaviour may be
reflected in the response properties of individual neurons in this brain region. Knowing that the Bogong moth can
chose a migratory heading based on the starry sky alone, I recorded from neurons in the central brain while
presenting the moth with a rotating starry sky (Paper III). I found several neurons that consistently responded to this
stimulus. Some of these neurons had branches in the optic lobes, the central complex or the lateral complex, which
are all associated with visual compass processing. Thus, these neuropils provide a suitable substrate for processing
compass cues during the moths’ nocturnal migration. Finally, I investigated how a compass signal in the central
complex is transmitted to downstream motor centres that coordinate wing and leg movement. To this end, I built a
computational model of a proposed steering network (Paper IV). I showed that this network can theoretically steer
based on input from olfaction as well as vision, providing a putative connection between the compass system in the
central complex and thoracic motor centres. Taken together, these results have not only shed light on the neural
basis of migration in the Bogong moth, but also on neural processing in the insect central complex and lateral
accessory lobes in general. In the future, combining these results with insights from other insects may lead to a
complete understanding of the neural basis of migration, from the sensory inputs to the behavioural output.

Details

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Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Zoology
Original languageEnglish
QualificationDoctor
Awarding Institution
Supervisors/Assistant supervisor
Award date2020 Jan 31
Place of PublicationLund
Publisher
  • Lund
Print ISBNs978-91-7895-382-0
Electronic ISBNs978-91-7895-383-7
Publication statusPublished - 2020 Jan 3
Publication categoryResearch

Bibliographic note

Defence details Date: 2020-01-31 Time: 13:00 Place: Blue Hall, Ecology Building, Sölvegatan 37, Lund External reviewer(s) Name: Ritzmann, Roy Title: Professor Affiliation: Case Western Reserve University, Cleveland, USA ---

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