June 4, 2018, University of Exeter
Tiny fish called Trinidadian
guppies turn their eyes black to warn other fish when they are feeling
aggressive, new research shows.
A study led by the University of
Exeter, in collaboration with the University of the West Indies, found that
when facing a rival, guppiesrapidly
turn their irises from silver to black before attacking their adversary.
This makes their eyes more
conspicuous and is an "honest" signal of aggression—larger guppies do
it to smaller ones whom they can beat in a fight, but smaller ones do not
return the gesture.
As part of the study, the
researchers made visually realistic robotic guppies to see what would happen if
smaller fish displayed
their aggressive motivation—and larger fish flocked in to compete with the
small imposters for food.
Dr. Robert Heathcote, lead author
of the study and from the University of Exeter, said: "Trinidadian guppies
can change their iris colour within a few seconds, and our research shows they
do this to honestly communicate their aggressive motivation to other guppies.
"Experimentally showing that
animals use their eye colouration to communicate with each other can be very
difficult, so we made realistic-looking robotic fish with differing eye colours
and observed the reaction of real fish."
Guppies rapidly turn their irises
from silver to black before attacking smaller rivals. Credit: Robert Heathcote,
University of Exeter
Professor Darren Croft, also from
the University of Exeter and an author of the study, added: "Eyes are one
of the most easily recognised structures in the natural world and many species
go to great lengths to conceal and camouflage their eyes to avoid unwanted
attention from predators or rivals.
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