If antelopes could smell lions stalking them upwind, then lions wouldn’t catch many antelopes. Smells travel in water as well as air, so a river predator should just stay downstream of prey and it will keep the element of surprise - right? Not quite, writes Richard Northover.
In Sweden, Jonas Dahl and colleagues at Lund University have found that Gammarus pulex, a small shrimplike animal, has a cunning adaptation for detecting potential predators waiting downstream. Its body shape creates small ‘backflows’ - turbulent areas in front of it where water, and chemical cues, flow upstream. Gammarus travels downstream at night, when light levels are low, and can smell predators and avoid them, before being seen and becoming fishfood.