Flying with Bogong moths: The first time an insect uses the stars to navigate in the high-seafields of the Northern Alps
In an interview with Francis Crick Institute’sneurobiologist, she claims that the Bogong moths of Australia are very little to look at. There are small brown moths with arrow-like markings on their wings. They are pretty nondescript.
There is a thought that the moths are guided by looking at the stars. To test this, they captured wild moths and placed them in a ‘flight simulator’ — a clear cylindrical box in which the insects were tethered and their movements recorded while being shown projections of the starry sky.
Adden says it’s the first time that they’ve found an animal using the stars to navigate. The first time that anyone had seen neurons in the insect brain that respond to the sky.
They hatch in their breeding grounds in the spring in southeast Australia where it gets really hot in the summertime. “So if they were to reproduce immediately, their larvae would starve because there is not enough food,” says Adden.
During their autumn and spring migrations, both sexes were caught in the wild with either a bumblebee light or a horizontal beam search light. Almost all of the animals were caught near the Mount Selwyn Snowfields (southeast New South Wales, Australia: 35.914° S, 148.444° E; elevation, 1,600 m), which is approximately 70 km north-northeast of the nearest aestivation cave in the Main Range of the New South Wales Alps. Thus, to reach these caves in spring, these moths (a tiny subset of all moths travelling to the mountains in a multitude of directions from across southeast Australia) would be expected to fly south-southwest in spring, and returning moths might be expected to travel north-northeast in autumn (which agrees with our behavioural results). Thredbo was also a location where a few animals were caught. These moths were used for electrophysiology only. Each captured moth was transferred to its own plastic container to isolate it from influence by other moths. After capture, moths were transported to the testing site Glenhare, a rural property near Adaminaby New South Wales (36.040° S, 148.864° E; elevation, 1,250 m), fed with 20% honey solution (in water) and stored in a cool and sheltered place (exposed to the natural light cycle) to recover from stress induced by capture.
The new moths hatch in the next year. They haven’t been to the mountains. They have no parents who can tell them how to get there.”
She suspected the stars might offer just the cue they need. She says the view of the Milky Way is stunning. “And it seemed an obvious thing to use if you are a moth living in that environment.”
Adden, who was doing her PhD at Lund University in Sweden at the time, and her colleagues ran two different experiments on moths in the dead of night in the Australian Alps to test her theory.
The first was a behavioral test. It involved placing a moths inside a miniplanetarium that had a projection of the night sky and no magnetic field.
“It’s not an experiment that always works,” says Adden. “We’re reliant on the moths cooperating with us.” Fortunately, enough moths did cooperate. And the result surprised the researchers.
The Optical Encoder of Dark-adapted Moths in an Indoor Lab (Extended Data Fig. 9b-d)
“They didn’t just circle and do twists and turns, but they actually chose a fairly stable direction,” she said. “Not only that, it was their migratory direction.”
She could see that most of the brain regions that deal with visual information were active when the moth was facing south. The direction shows that the brain of the moths is processing the visual images of the Milky Way.
An indoor lab located at Glenhare Adaminaby was designed to be ferromagnetic-free and was used for both behavioural and neurological studies. 1c). Each experiment has its own special earth separated from the mains earth through a 12-m long copper strap buried below the concrete slab. At this rural site, there are very low background levels of radio-frequency interference. All of the experiments were done on dark-adapted moths, which glow in the dark at night. Black out blinds and dark cloth covering the experimental apparatus were used to achieve darkness.
For tethering within the behavioural arena (performed in dim red light to maintain a dark-adapted visual state), the arena lid holding the optical encoder was lifted and the tungsten stalk of a vigorously flying moth (held with medical forceps) was attached to the bottom end of the encoder shaft through a 1.5 cm length of thin rubber intravenous medical tubing that connected the stalk to the shaft (Extended Data Fig. 1e). Once the lid was brought back to the arena, there was a mechanism that allowed the insect to choose any flight direction. Once the moth was mounted in the arena, it was gently pointed manually towards geographical north. The heading direction count was reset and the optical Encoder was allowed to register the flight heading direction at a sampling rate of 5 frames per second under a nighttime sky condition. The insects were tested for 5 min in each condition.
Upward light intensity and spectrum measurements of the starry night sky were made underneath the projection screen in each rig with the probe located at the position of the moth (Extended Data Fig. 9b–d). The light metre used was a calibrated Ocean Optics QE65PRO The Ocean Optics Spectrometer is a tool for studying the ocean.
It was important to confirm the difference in the flight directions between nature and sky conditions for any single sky condition.
Brains of butterflies in the Amira v.5: micromicroscopy and MRI microscopy during the migratory season
Brain samples were scrutinized with a microscope and objective that looked like 20 oil-immersion points. For optimal resolution, the scan settings were set to 1,024 × 1,024 pixels, 12-bit pixel depth, 3 times line accumulation and 400 lines per s in the photon-counting mode of the hybrid detector. The brain of a butterfly was registered into the standard brain in Amira v.5 and Amira v.6.
The P-97 Flaming-Brown micropipertte had a typical resistance of 50– 100 M and was capable of pulling glass electrodes from borosilicate glass. The rest of the electrode was filled with 1 M KCl and the tip was filled with 4% Neurobiotin. Electrodes were moved into position with a non-magnetic Sensapex micromanipulator. Signals were recorded using Spike2 software, used to amplify signals using the BA-03X amplifier and headstage (NPI Electronic), and then digitally uploaded using the CED Micro 1401-3 (Cambridge Electronic Design). The signals from MATLAB were recorded in Spike2. During the recording, the brain was kept hydrated with moth ringer solution47.
We target an area in the brain where we expected to find a wide range of cells, as well as a specific part of the brain in the back of the eyes. They discarded the neuron that did not respond to the initial sky rotation. 79 neurons were assessed as potentially responding to the stimulus and, of these, 28 (35%) met the inclusion criteria of a unimodal or bimodal response profile. The remaining 51 neurons were classified as uniform in their response to stellar rotation (that is, showed no obvious response) and were therefore excluded from the analysis.
To maximize the success rate of the demanding intracellular recordings during the short migratory season, these experiments were performed both in the afternoon and during the natural nocturnal flight time of the moths. For afternoon experiments, we removed the two 1.2 log unit ND filters in front of the projector lens (as described above) to generate a starry sky projection around 250 times brighter than the one used at night (to account for the circadian-rhythm-induced light-adapted state of the moths). For night experiments, the ND filters were reinserted. The results were obtained in two different situations. The moths were shorn off of the custom-made 3D-printed animal holder. The brain was exposed with a square piece of the cuticle being removed from the head capsule. The neural sheath was digested with Pronase (Sigma-Aldrich) for about 30 s and then carefully washed. It was removed using a pair of sharp instruments. A second small hole was cut into the cuticle above the proboscis muscle and a chlorinated silver wire was inserted into this muscle to serve as reference electrode.
Most procedures used in this study have been described before. Before attachment of tethering stalks, moths were chilled in a freezer for 5–10 min to immobilize them. The scales on the thorax of a caterpillar were removed using a micro-vacuum pump. A thin vertical germano stalk was created to create a small circular footplate and was fastened to the thorax using contact cement and a weighted down plastic mesh. There were Moths on the day of the attachment.
Source: Bogong moths use a stellar compass for long-distance navigation at night
Improved Randomized Starry Sky Images for a Detecting Spike Train in 2019 and its Visualisation Using a Custom-made LED Ring in Front of a Projector
The positions of the individual stars of the natural night sky image were changed to new positions randomly and the resulting randomized images were saved asPNG files. 9a). These featureless stellar conditions provided an identical stimulation intensity but provided no celestial spatial information. The randomized starry skies used during spring and autumn 2019 were improved by randomizing groups of pixels containing individual stars, therefore retaining the stars but removing spatial variations in the night sky (such as the Milky Way) that could be used for orientation (again maintaining identical intensity). Here, the image was divided into squares of 13 13 pixels as the star in the image was roughly the same size. The positions of these squares were now randomly reassigned and the resulting image was saved as a PNG file. Randomising the positions of individual visible stars was used to Generate a final Improved RandomizedStimuli. The position and size of each star were detected using a multi scale Laplacian of a greyscale version of the test stimulus, before the local maxima detection. The resulting spatial information was used to make a new background image of the stars in the sky, with the same intensity and colour as the original test image, but instead of being part of a star. The location of the stars on the randomized image is drawn from any desired distribution. A uniform distribution was used to place the star in the middle of the image.
The projector did not emit UV light and as a result, we installed a custom-made 120mm diameter LED ring in front of the projector. Several layers of ND filters were fixed in front of the LEDs to bring the UV intensity into a natural range, and custom written software was used to adjust the brightness of the LEDs.
Spike train data were analysed using custom-written code in MATLAB (v.2019a and 2022b, MathWorks). Circular statistical analysis was done in R using the maximum-likelihood estimation package. Responses were classified as unimodal (models M2A, M2B or M2C in the R-library CircMLE) or bimodal (models M4A or M4B) based on the Akaike information criterion. Only responses that were classified as unimodal were analysed further with regard to the half-width of the rotation tuning curve.
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Diverse ecosystems could help modern humans migrate out of the continent around 50,000 years ago: Humpback whales try to communicate with humans through blowing bubble rings
New research suggests that shortly before modern humans successfully migrated out of Africa, they massively expanded the range of ecosystems they lived in. By combining climate modelling with data from archaeological sites across the African continent, researchers put forward evidence that 70,000 years ago, humans expanded the ecosystems they lived in to include diverse habitat types from forests to deserts. The authors suggest this ability to live in different places may have helped the later humans that migrated out of the continent around 50,000 years ago.
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“The first time we saw them flying under the night sky with no other cue and flying in the right direction we had to hold on to the edge of the table,” says study co-author Eric Warrant, an entomologist at Lund University in Sweden.