Essay About Trichromatic Colour Vision And Primate Colour Vision

Color Vision
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Evolution and selection of trichromatic
vision in primates
Alison K. Surridge1, Daniel Osorio2 and Nicholas I. Mundy3
1School of Biological Sciences, University of East Anglia, Norwich, UK NR4 7TJ
2Biological Sciences, University of Sussex, Brighton, UK BN1 9QG
3Department of Zoology, University of Cambridge, Cambridge, UK CB2 3EJ
Trichromatic colour vision is of considerable importance
to primates but is absent in other eutherian mammals.
Primate colour vision is traditionally believed to
have evolved for finding food in the forest. Recent work
has tested the ecological importance of trichromacy to
primates, both by measuring the spectral and chemical
properties of food eaten in the wild, and by testing the
relative foraging abilities of dichromatic and trichromatic
primates. Molecular studies have revealed the
genetic mechanisms of the evolution of trichromacy,
and are providing new insight into visual pigment gene
expression and colour vision defects. By drawing
together work from these different fields, we can gain a
better understanding of how natural selection has
shaped the evolution of trichromatic colour vision in primates
and also about mechanisms of gene duplication,
heterozygote advantage and balancing selection.
Among eutherian mammals, primate vision is unique.
Across primate taxa, colour vision is remarkably diverse
and studies of how and why such vision has evolved span
many fields in ecology and evolution. Although vision is
clearly of interest to those studying primate behaviour and
forest ecology, the underlying genetics of colour vision
provide important insights into polymorphism and population
genetics and also into the evolution of gene function
and regulation.
Our knowledge of the genetic basis for colour vision now
enables us to understand how it evolved, but much work
still focuses on why colour vision evolved. Such theories
are often controversial, and can be difficult to test. One
long-standing hypothesis is that enhanced colour vision in
primates evolved to detect ripe fruit on a dappled background
of leaves [1,2]. In the past few years however, this
has been challenged by the idea that foraging for young
leaves, which are often red in colour, explains such
adaptive variation [3,4]. A recent finding indicates that
primate colour vision might have evolved much earlier
than was previously thought, and provides some evidence
that an ancestral primate was possibly diurnal rather than
nocturnal [5]. However, paleontologists and taxonomists
tend to disagree [6]. Interestingly, in some primate taxa,
the variety of colours that can be discriminated differs,
even among individuals of the same species and sex. This
polymorphism enables a direct comparison of individual
primates with a variety of colour vision phenotypes to be
made, and links differences in a single gene to changes in
behaviour. Emerging experiments can now test models of
natural selection that were first proposed some 20 years
ago [7]. These studies follow the behaviour of individual
animals whose genotype and phenotype are known, and
provide an exciting way forward for understanding the
mechanisms of selection.
Seeing colours
Vertebrate colour vision requires both the presence of
PHOTORECEPTOR (see Glossary) cells, called CONE CELLS, in
Glossary
Allelic trichromacy: trichromatic vision achieved through the presence of
multiple alleles at the single X-linked opsin locus. Only females can be