New research published in the journal Current Biology has uncovered a clever trick used by guppies to avoid predators. Much like matadors waving their provocative red capes, guppies focus a predator's point of attack before dodging away at the final moment to avoid injury.
Much as I’d love to write that the guppies in question arm themselves with tiny matador capes, they instead draw the attention of their attackers by turning their irises black. This makes the tiny fishes’, which are around 10 to 40 millimeters (0.3 to 1.6 inches) in length, easy to spot. Their main predator is pike cichlids, and the guppies will often approach them to test the waters in seeing if they are currently hungry and on the prowl or not. Their darkened eyes provoke the cichlids to charge at their head instead of their body, and if they take the bait, the guppies use their rapid reflexes to whip away at the last moment and escape.
"We noticed that guppies would approach a cichlid at an angle, quickly darkening their eyes to jet-black, and then waiting to see if it would attack," said lead author Dr Robert Heathcote, who undertook the experimental work at Exeter and is now at the University of Bristol, in a statement. "Whilst it seems completely counterintuitive to make a predator attack your head, this strategy works incredibly well because guppies wait until the predator commits to its attack before pivoting out of the way."
The predator-prey interaction was so speedy, at around three-hundredths of a second, that it could only be observed using a high-speed camera. When the guppies make their presence known with their darkened eyes, they're using “conspicuous coloration”, which is the behavior seen in a diverse range of species trying to attract a mate, intimidate predators, or advertise their own toxicity. The matador-like evasion technique, however, is one that hasn't been observed before but the researchers think that it’s likely also employed by other species.
"We don't know for sure, but it seems highly likely that other animals also use a 'matador' strategy like the one we have identified in guppies," said Professor Darren Croft, of the University of Exeter. "Eyes are one of the most easily recognized structures in the natural world and many species go to great lengths to conceal and camouflage their eyes to avoid unwanted attention from predators. Some species, however, have noticeable or prominent eyes and, for the most part, it has remained a mystery as to why this would be.
"Our latest research gives new insight into why 'conspicuous' and colourful eyes have evolved."