20
UWI TODAY
– SUNDAY 1 JULY, 2018
LIFE SCIENCES
Suppose you meet a mortal enemy
and combat seems
imminent. What if, then, your eyes suddenly turned an
inky-black colour, to signal to the enemy that you’re a
powerful warrior who can easily whip him in a fight?
That, in a nutshell, is what the humble Trinidad
guppy does when it’s getting ready to rumble, especially
if other guppies or other fish are threatening to steal its
valuable food. A study led by the University of Exeter,
in collaboration with the University of the West Indies,
found that when facing a rival, guppies rapidly turn their
irises from silver to black before attacking their adversary.
In TT creole culture, you could humorously say it’s like
the guppy version of “cut-eye.” It’s a built-in biological
mechanism that helps the tiny fish communicate its
aggression.
The guppy eye colour change 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, say
University of Exeter researchers.
Our own UWI St Augustine Deputy Principal,
Professor Indar Ramnarine, was part of this research
team and co-author of the recently published paper
on the guppy eye change, called “Dynamic eye colour
as an honest signal of aggression”, and published in
the journal Current Biology. The Exeter team is one of
several research teams fromdifferent universities around
the world with whom Prof Ramnarine works, pursuing
different projects. Ramnarine is Professor of Fisheries and
Aquaculture at the UWI Department of Life Sciences.
In a recent interview with UWI Today, he said:
“I’ve been collaborating with Professor Darren Croft
from the University of Exeter for the past 15 years. Dr
Robert Heathcote, lead author of the study and from the
University of Exeter, joined the research group about four
years ago. The fascinating characteristic about guppies is
that they are an ideal model to study evolution. Females
mature in just 10 weeks while males take seven weeks.
And they can live for about four years. That means there
is a quick turnover, with lots of generations to study.”
“Guppies are native to North-East South America
and Trinidad, with the males being smaller and more
colourful than the females. In Trinidad’s Northern Range,
Guppy
‘Cut-Eye’
Trinidad guppies
turn their eyes from
silver to black when
they’re ready for a fight
B Y S H E R E E N A N N A L I
The research paper “Dynamic eye colour as an honest signal of aggression” was published in the journal Current Biology, Volume 28, Issue 11, on June 4, 2018,
and was based on research done in 2016 and 2017. Its authors are Robert J.P. Heathcote, Safi K. Darden, Jolyon Troscianko, Michael R.M. Lawson,
Antony M. Brown, Philippa R. Laker, Lewis C. Naisbett-Jones, Hannah E.A. MacGregor, Indar W, Ramnarine, and Darren P. Croft.
there are natural barriers such as cascades, and these
separate two distinct guppy populations that behave
differently. Above the cascade barriers, there are hardly
any natural predators, and guppies here mature later in
life, have fewer baby guppies per pregnancy, and these
young are large. Below the natural barriers, the guppies
encounter many more predators – mainly the matawal
or pike cichlid, and the guabine or wolf-fish – and these
guppies mature much earlier in life, and have large
numbers of live young which are smaller in size than
guppies in the safer waters upstream.”
“Darren (Croft) and I were in the lab one day and
we noticed the iris colour change from silver to black
and thought, there must be a reason. Then Dr Robert
Heathcote joined the team and led this study.”
Heathcote with his colleague Jolyon Troscianko had
the idea to build latex models of guppies. Troscianko
studies animal camouflage. Science writer Ed Young
clearly describes the process of building the simulated
guppies in his lively June 4 article in The Atlantic
magazine:
“The team pressed a dead fish into some resin to
make a siliconmold that could churn out model guppies.
They then photographed live fish with black and silver
eyes, recalibrated the images for guppy vision, and
printed them onto sheets of clingfilm. They stretched
the coloured sheets over the silicone models, which they
attached to a fishing line on a motor.”
And just like that, they had great imitation guppies
whichcouldbemade todefendand thrashover abit of food.
Dr Robe r t Heat hcote s ai d of t he s tudy :
“Experimentally showing that animals use their eye
coloration to communicate with each other can be very
difficult, so we made realistic-looking fish with differing
eye colours and observed the reaction of real fish….
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.”
Professor Darren Croft 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. However, some species have
noticeable or prominent eyes and, for the most part, it
has remained a mystery as to why this would be. This
research gives a new insight into the reasons behind why
some animals have such ‘conspicuous’ eyes.”
Dr Safi Darden co-author on the study added: “It is
well known that in humans the white sclera of the eye
is used to signal gaze direction – it provides others with
information on what we are looking at. Our work shows
that just like humans, these little fish pay attention to the
eyes of their group members and that the eyes provide
important information to other rival fish”.
Prof Ramnarine comments: “Different animals
respond differently to threats. A pufferfish, for instance,
takes in water or air to make itself seem huge; other
animals also make themselves seem larger or fierce.
It’s an important strategy in the animal kingdom when
creatures come into conflict with each other. This guppy
study shows that fish can evolve a complex behavioural
strategy to communicate with other fish that they are
willing to fight.”
A recently published study shows that
guppies can change their eye colour from
silver to black to signal aggression. Guppies
are model species for studying evolution in
the wild. The rivers in the Northern Range
have natural barriers such as cascades and
waterfalls which prevent major guppy
predators from inhabiting upstream areas.
This has resulted in guppies living upstream
(low predation sites) being quite different
from guppies living downstream (high
predation sites) in terms of life history,
morphology and behaviour.
Robert Heathcote, Associate
Research Fellow, University
of Exeter
Safi Darden, Lecturer,
University of Exeter
Darren Croft, Professor
of Animal Behaviour,
University of Exeter
Indar Ramnarine, Professor of
Fisheries and Aquaculture, UWI
