Colour blindness gives monkeys a helping hand

Published: 11 January 2012 at 13:07

Anglia Ruskin scientist discovers dichromats are better at catching camouflaged prey

An Anglia Ruskin University scientist has discovered that colour blind monkeys are better at catching camouflaged prey than monkeys with “normal” eyesight.

Dr Andrew Smith, from Anglia Ruskin’s Department of Life Sciences, led the project, which also involved scientists from the University of Stirling, the University of Cambridge and the University of Sussex, and the results have been published in the journal Animal Behaviour.

While studying three species of tamarin monkey – saddleback, moustached and red bellied – in the Amazon rainforest in Peru and in captivity at Belfast Zoo, Dr Smith found that levels of colour vision affects the rate and type of insect capture.

Tamarins with normal colour vision (trichromats) catch more prey than colour blind tamarins (dichromats).  However, the colour blind tamarins were significantly better at catching camouflaged insects, such as crickets.

Dr Smith said:

“Colour blindness has several possible advantages for the tamarins.  There is evidence in humans that dichromats see better in dim light than trichromats, it is thought that dichromats may have improved spatial vision and, crucially, dichromats appear to be superior at visually breaking camouflage.
“Experiments have shown that colour blind humans and nonhuman primates are better able to detect targets based on texture or outline while for colour normal humans and primates the target is camouflaged by colour.  This means that colour blind wild primates actually have an advantage in their natural habitat when it comes to detecting both camouflaged prey and predators.”

Monkeys and apes are thought to have evolved good colour vision to help them find ripe fruit in trees, which is often a red or orange target against a green background.  Colour blindness, most commonly the inability to tell red from green, is more common in humans than in other apes, possibly due to the fact that for apes, such as chimpanzees and gorillas, not being able to find ripe fruit is more of a disadvantage than it is for the average man.

Unlike Old World monkeys, apes and humans, New World monkeys from Central and South America have colour vision that varies between individual members within each species.  For most New World monkeys all males and some females are colour blind, but some females have normal colour vision similar to that of most humans.  

However due to a genetic quirk, New World monkeys such as tamarins routinely have six types of colour vision; three types of colour blindness (dichromacy) and three types of colour normal vision (trichromacy).  The scientists were able to discover the type of colour vision of an individual wild monkey by examining DNA extracted from faeces collected from the forest floor.

“It is possible that in a group of six tamarins, no two members would see the world in the same way,”

added Dr Smith. 

“This could provide greater scope for an individual group member to be relatively better or worse than the other members at particular visual tasks.
“This could have major advantages for the group as it relieves competition, as they would each be able to specialise on different tasks such as catching camouflaged prey or finding fruit.  It might also help to explain why such a seemingly contradictory system of both colour blind and colour normal monkeys is maintained in natural populations.”