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How a ‘sky compass’ helps fruit flies navigate

Researchers have shown that, similarly to other insects, fruit flies use polarised light in the sky to help themselves navigate.
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New insight on how fruit flies orient themselves and navigate using patterns of polarised light in the sky has been published today in eLife.

Fruit flies at rest. Image credit: Jim McLean (CC BY-NC-SA 2.0)

The study highlights the underlying neural circuitry that allows flies to use polarised light for navigation, and paves the way for further research into how these insects integrate other sensory information when travelling.

Previous studies have shown that other types of insects, such as butterflies, bees and beetles, use patterns of polarised light to navigate, in part, because these patterns may be more reliable than physical landmarks. Insects are able to see the patterns in the sky and the nervous system deciphers them, essentially giving each animal a built-in compass. The neural circuits that enable this process are known as the ‘sky compass’ pathway. But these circuits had not previously been mapped in Drosophila fruit flies, an insect that is commonly used in many types of scientific research.

“Knowing which direction to go is a fundamental challenge for all moving animals, whether it’s to find food, find home, or just to avoid becoming lost,” explains lead author Ben Hardcastle, Postdoctoral Scholar at the Department of Integrative Biology and Physiology, University of California, Los Angeles, USA. “Mapping the sky compass pathway in fruit flies allows us to use the many genetic tools available for studying Drosophila to better understand how they and other insects use polarisation patterns to navigate. This insight could also inspire new approaches to designing efficient, low-power electronic circuits for guiding autonomous robotic platforms.”

In their study, the team mapped the circuits that relay polarised light signals from the nerves in the eye and brain regions responsible for vision to the part of the fly’s brain that gives it a sense of direction.

“Vision by polarised light is hard for us to imagine, since we can’t see it, but many animals including flying insects use polarised light to navigate,” says co-senior author Mark Frye, Professor of Integrative Biology and Physiology, and Neurobiology, at the University of California, Los Angeles. “How does it work in the brain? We show that each section of the fruit fly visual pathway has nerve cells tuned to specific angles of polarisation. Together these create a circuit that relays polarised light signals from the eye to compass nerve cells in the center of the fly brain.”

“Our study lays the groundwork for further research into how the brain in flies and other insects translates complex light information into behaviours,” concludes co-senior author Volker Hartenstein, Professor of Molecular, Cell and Developmental Biology, University of California, Los Angeles. “A key challenge for future studies will be to uncover how fruit flies integrate other kinds of sensory information to help them navigate in complex environments.”

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