The bunfight at the poo pile

Dung beetle in sun cap
It’s almost like they have a Swiss Army knife of skills to deal with the orientation problem, but there must be one skill set that is the absolute minimum requirement.
Professor Marcus Byrne
Researchers from South Africa and Sweden have found that certain species of dung beetle use the line of stars that make up our galaxy to steer themselves away from potential competitors. Despite the beetle’s tiny brain and poor eyesight, they have become the first animals documented as using the Milky Way as an orientation tool.

The research findings were published in the Cell Press journal Current Biology this week. While there are around 800 species of dung beetle in South Africa alone, this study focused on just one of several nocturnal species.

Professor Marcus Byrne, teaches zoology and entomology at the University of the Witwatersrand (Wits University) in Johannesburg. He collaborates with Professor Clarke Scholtz of University of Pretoria and Professor Eric Warrant and Dr Marie Dacke of Lund University in his work on orientation in dung beetles; work which may enable humans to solve difficult visual processing problems. Professor Byrne spoke to whilst out doing fieldwork and outlined both what has been found and the impetus of current research.

Other researchers have provided evidence that various animals are able to use celestial bodies for orientation, and indeed Professor Byrne and his colleagues have already shown that members of the dung beetle family are able to use the sun, the moon and polarised light as visual cues.

"We know that seals, for instance, can orient themselves by the stars and there is also evidence that some species of frog do the same," said Professor Byrne. "As far as we’re aware, this is the first time that anybody has looked at the Milky Way per se in terms of orientation."

For the dung beetles, aligning their paths with a distant light source is valuable way of reducing competition. Professor Byrne likens the situation to a buffet, where you have to grab what food you can and move away from the buffet table as quickly as possible. To avoid circling back and meeting rivals for resources at the dung pile, they use the stars to ensure they travel in a straight line.

"By heading off in a straight line you no longer need to know where you’re going, as long as you know where you’ve been," the professor explained.

In their previous experiments, the researchers blocked light from reaching dung beetles by fitting them with miniature caps. They observed the beetles performing a so-called ‘orientation dance’ to get their bearings on top of their balls of dung. After conducting further experiments with the nocturnal species in the simulated environment of the Wits Planetarium, Professor Byrne and the team are trying now to unravel exactly which different environmental cues the dung beetles use, and to find out whether a hierarchy of preference exists amongst these cues.

"We are studying a nocturnal species so the beetle can’t use the sun, but it would be able to use the moon – specifically, polarised light from the moon – and the Milky Way itself is another cue," he said.

Both create a light intensity gradient across the sky; if the moon is out the sky will be brighter on one side and darker on the other. The team are very pleased by the fact that they have been able to isolate the Milky Way’s array of stars as one of the dung beetle’s points of reference.

As Professor Byrne pointed out, if you walk a few metres across the planet, the sun appears to stay in one place, but if you walk past a light its location will appear to move from in front of you to behind you. A moth which keeps its body at a constant angle to a candle will move in a circle around the flame. I was curious about the potential effects of light pollution on the dung beetle’s ability to effectively make a fast getaway from dung piles.

"We do our work out in the bush; at the moment we are 70 km from the nearest big town," Professor Byrne stated. "There is a very, very faint glow on the horizon, and that wouldn’t affect the behaviour of the beetles, but certainly bright lights in cities affect the orientation of insects because they’re completely unnatural.

"Light pollution does affect animal orientation and in this case it will almost certainly swamp any cues," he affirmed.

One of the reasons Professor Byrne cites for carrying out the research on this particular insect is that they are absolutely tenacious. The predictability of the beetle’s behaviour means it can be relied on always to do exactly what it wants to do, which is to roll a ball. This means that all sorts of questions can be answered by studying it.

"The questions we’re asking at the moment are to do with the light intensity gradient across the sky, and also how temperature affects the beetle’s orientation," confided Professor Byrne. "We’re trying to find out exactly how the hierarchy of cues works.

"It’s almost like they have a Swiss Army knife of skills to deal with the orientation problem, but there must be one skill set that is the absolute minimum requirement. That’s what we’re ultimately looking for – the absolutely basic orientation cue that the beetle needs to find its way around."

Although, as Professor Byrne admitted, this study about the dung beetles may appear to be trivial in itself, by finding out how an insect with only 200,000 or so neurons solves a fairly complex orientation problem, we may gain the knowledge needed to build machines able to do the same with minimal computing power. However, that’s not the only purpose of the research.

"It’s not just about answering blue-sky questions," Professor Byrne insisted. "It has to be fun!"



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