A major task completed during the project – and which was (and will be) essential for our progress – was the construction of a new magnetic-free laboratory building at our field site in Australia (which is free from magnetic artefacts: Fig. 2). This is the only lab building of its kind in the southern hemisphere and only the second magnetic-free lab building in the world. This lab houses a non-magnetic electrophysiology rig (with Helmholtz coils to provide precise Earth-strength magnetic stimulation – Fig. 2C-D) and a behavioural arena (also with Helmholtz coils – Fig. 2F,G). We also replicated the non-magnetic electrophysiology lab in Lund.
The results of our project are as follows:
1. We have shown that nocturnal migratory insects - like nocturnal migratory birds - sense the Earth’s magnetic field and rely on it to determine compass directions (N, S, E and W) to steer migration in the inherited migratory direction (Fig. 3), which is a major discovery (and currently being repeated). We also investigated whether the Bogong moth magnetic sense is based on a light-dependent radical pair mechanism present in cryptochrome molecules. Unfortunately our attempts to localise where in the nervous system these cryptochromes reside (thus revealing the possible location of the magnetoreceptor) have so far been inconclusive. Moreover, the riskiest part of the project has also not succeeded so far (despite a large effort) – identification and characterisation of the elusive magnetic sensor and the higher-order cells in the brain that process magnetic information.
2. We have shown that the Bogong moth uses the Australian starry night sky as a true compass to steer migration in the inherited migratory direction (Fig. 4), the first invertebrate known to do so (the only other animals known to possess this ability are humans and some species of night-migratory birds). Moreover, the moths are able to compensate for the nightly rotations of the stars in order to maintain a constant migratory heading. These are also major discoveries. In addition, we have determined the structure of the Bogong moth brain [1] identified a number of visual cells in the moth’s central brain that respond exclusively to rotations of the starry night sky, and which are therefore likely to be involved in the stellar compass network that analyses stellar information to set and correct the migratory course (Fig. 5). This work is currently being written up for publication in Nature.
3. We have sequenced and annotated the genome of the Bogong moth. This is allowing us (and others) to ask a number of very important fundamental questions regarding the biology, ecology, conservation, migration and sensory biology of this keystone species (whose mass migration to the Australian Alps is critically important for the health of the alpine ecosystem). This work is currently being written up for publication in iScience.
4. We used the new genome to show that the Bogong moth population has no genetic structure (i.e. it is panmictic: [2]). Nonetheless we were able to show that there are four genetic loci tightly coupled to the geographic origin of the moths, and thus to the inherited migratory direction, suggesting that the migratory direction is indeed passed down from generation to generation at each geographical location within the vast breeding grounds of the Bogong moth.
5. We have pioneered new methods for detecting and tracking migrating insects [2-7]. Our new automatic camera tracking system (“Camfi”) and our new vertical LIDAR system (Fig. 6), coupled with traditional vertical radar, will allow us and others to identify, monitor and track insects during their migration with unprecedented clarity. These methods are currently being used in the field to monitor populations of the endangered Bogong moth, and can be used for monitoring the health of insect populations in regions of the world where their decline is extremely worrying.
[1] Adden, A., Wibrand, S., Pfeiffer, K., Warrant, E.J. and Heinze, S. (2020). The brain of a nocturnal migratory insect, the Australian Bogong moth. Journal of Comparative Neurology 528: 1942-1963. doi: 10.1002/cne.24866.
[2] Wallace, J.R.A Maleszka, R. and Warrant, E.J. (2023). Large-scale whole-genome sequencing of migratory Bogong moths Agrotis infusa reveals genetic variants associated with migratory direction in a panmictic population. Manuscript. bioRxiv 2022.05.27.49380 doi.org/10.1101/2022.05.27.493801
[3] Hao, Z., Drake, V.A. Taylor, J.R. and Warrant, E.J. (2020). Insect target classes discerned from entomological radar data. Remote Sensing 2: 673. doi:10.3390/rs12040673.
[4] Drake, V.A. Hao, Z. and Warrant, E.J. (2021). Heading variations resolve the heading-direction ambiguity in vertical-beam radar observations of insect migration. International Journal of Remote Sensing 42: 3873-3898.
https://doi.org/10.1080/01431161.2021.1883202(s’ouvre dans une nouvelle fenêtre)[5] Li, M., Seinsche, C., Jansson, S., Hernandez, J., Rota, J., Warrant, E.J. and Brydegaard, M. (2022). Potential for identification of wild night-flying moths by remote infrared microscopy. Journal of the Royal Society Interface 19: 20220256. doi.org/10.1098/rsif.2022.0256
[6] Wallace, J.R.A Reber, T., Dreyer, D., Beaton, B., Zeil, J. and Warrant, E.J. (2023). Camera-based automated monitoring of flying insects (Camfi). I. Field and computational methods. Frontiers in Insect Science 3:1240400. doi.org/10.3389/finsc.2023.1240400.
[7] Wallace, J.R.A Dreyer, D., Reber, T., Khaldy, L., Mathews-Hunter, B., Green, K., Zeil, J. and Warrant, E.J. (2023). Camera-based automated monitoring of flying insects in the wild (Camfi). II. Flight behaviour and long-term population monitoring of migratory Bogong moths in Alpine Australia. Frontiers in Insect Science 3:1230501. doi.org/10.3389/finsc.2023.1230501
