Different dung beetle species use different celestial cues for navigation

Some beetles prefer the patterns of the stars, while others like the direct glow of the moon and sun.

By Brooks Hays

TUCSON, Aug. 25 (UPI) -- Dung beetles are one of only a few insects known to use celestial cues for navigation, but until now, scientists didn't really know how they did it.

New research suggests their use of skyward navigational beacons is dependent on their species, specifically on whether the dung beetle is diurnal or nocturnal. Depending on the time of day, the light conditions and the lunar calendar, the beetles use varying celestial cues to roll their balls of excrement in a straight line.


A team of researchers -- scientists from the University of Arizona and Sweden's Lund University -- discovered the beetles' navigational methods by placing specimens in an enclosed space where celestial cues could be simulated and manipulated.

By playing around with various sources of light while monitoring the specimens' neurons using electrophysiological instruments, researchers were able discern which beetles paid attention to which cues.

Their experiments proved that nocturnal beetles primarily use the polarized skylight patterns -- provided by the scattered glow of the moon and stars -- in the nighttime sky to navigate their darkened surroundings. When nocturnal beetles are coaxed into daytime movement, they use direct rays of the sun to orient themselves.


Diurnal beetles, on the other hand, use celestial bodies during both the day and night. Navigational neurons in the brains of diurnal beetles are attuned exclusively to sunlight -- whether direct or bouncing off the moon -- whereas the neurons of nocturnal beetles can switch between polarized light patterns and direct light from celestial sources.

"These neurons encode the preferences for particular celestial cues and alter their weighting according to ambient light conditions," researchers wrote in their new paper on the subject, published in the journal PNAS. "This flexible encoding of celestial cue preferences relative to the prevailing visual scenery provides a simple, yet effective, mechanism for enabling visual orientation at any light intensity."

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