South African dung beetles compete fiercely for the chance to eat the poop of other animals. When a beetle comes across a pile of dung in the savannah, it quickly cuts off a piece, rolls it into a ball, and heads off in reverse with its stinky prize, away from other hungry beetles. To efficiently escape with their trophy, the beetles move in a straight line, orienting themselves with celestial objects such as the sun or moon. However, new research from Marie Dacke and colleagues from Swedish, German and South African universities suggest that the beetles can also steer based on changes in wind direction.
First, Dacke and colleagues tested whether beetles in their natural habitat steer dung balls in a straight line using cues from the wind in addition to the celestial cues they are known to use. The researchers tested the beetles when the sun was at three different positions above the horizon – low (15–30 deg), medium (45–60 deg) and high (>75 deg) – and observed whether they continued to roll their dung balls in the same direction in response to a 180 deg artificial change in wind direction. When the sun was at its highest elevation and the experimenters switched the direction of the wind, the beetles started rolling their dung balls in the opposite direction. However, when the sun was at the lower elevations, the beetles kept rolling their balls in the same direction no matter how the wind changed. This suggests that the beetles orient themselves based on a single cue at a time, either the sun or the wind, and that they might, in fact, have a ‘wind compass’ they use when the sun is high in the sky.
The team then took the beetles back to the lab to better understand how they coordinate using wind and sun cues. First, the scientists changed the number of sensory inputs the beetles received between each roll of their dung balls forward: they provided the beetles with multiple inputs on their first rolls (wind from a fan and a bright light to mimic the sun, set perpendicular to each other). They then removed one of the inputs during the second revolution of the dung ball – leaving the insects to navigate either by artificial ‘wind’ or a fake ‘sun’ alone. In response, the beetles continued rolling their dung balls in straight lines despite switching from multiple to individual sensory inputs, which was surprising, as under natural conditions in the savannah the beetles seemed to position themselves based on one sensory input at a time. However, the beetles’ ability to continue moving in a straight line suggests that they store directional information from both the wind and the sun in their internal compass systems. The researchers then tested whether orientation information from the sun and wind sensory systems can be stored and exchanged between different brain areas. They realised that the beetles were able to depend on directional information from the sun and moon collected at different times, suggesting that information from the two systems is shared somewhere in the brain.
Dacke and colleagues are the first to show that wind is important for helping South African dung beetles roll away from hungry competitors with their dinner. Additionally, their research highlights that information from the wind and the sun might be stored in the same place in the beetles’ brains. For an animal that feasts on other animals’ poop, the South African dung beetle has quite a sophisticated navigation system.
