Re: Most mammals evolved to be color blind

In message <1174767380.652364.165470@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, Robert Carnegie <rja.carnegie@xxxxxxxxxx> writes

dkomo wrote:

Except for primates, mammals are dichromatic and are red-green color blind.

"All apes and Old World (African and Asian) monkeys have trichromatic
vision, which allows them to see across the visible spectrum from blue
to green to red. Most other mammals are dichromats -- they can see blue
and yellow hues but cannot perceive or distinguish red from green."

--Sean Carroll, _The Making of the Fittest_, p. 92

Whales and dolphins are monochromats -- they have no color vision at all.

On the other hand, birds have fabulous color vision. Many species of
birds can see in the ultraviolet. Reptiles and many fish also have good
color vision. Color vision must have been present in the earliest
vertebrate ancestor of fish, birds, reptiles and mammals.

So how come modern mammals came to be impoverished with respect to color
vision? The answer is that the original ancestors of mammals were small
nocturnal critters, and this shifted the dependence of these animals
from color vision in bright light to vision in dim light and darkness,
and full color vision was lost.

Is this right? Couldn't colour vision be evolved separately in
different lineages? To put it another way, is there evidence of
common descent? There are literally dozens of separately evolved
eyes, I hesitate to agree that genes for colour vision are conserved
when you don't have eyes. And I don't think whales are descended from
birds, and primates from whales.

I assume that colour vision in arthropods, molluscs and vertebrates did evolve independently. In vertebrates colour vision appears to be basal - or perhaps basal to a large subclade (including at least bony fish and tetrapods).

It is believed that mammals lost some of their colour vision, becoming dichromats, due to adopting a noctural lifestyle - hence the selection pressure for retaining "full" colour vision was reduced. Trichomatacy was regained independently in Old World Primates and a subclade of New World Primates. (And also partially in some lemurs.)

In fact, it should be fairly straightforward to find the similar
colour genes in different species where they /do/ have a common
origin.

A little digging in Google Scholar turns up

* Jacobs & Rowe, Evolution of vertebrate colour vision, Clin Exp Optom 2004; 87(4–5): 206–216 (2004)

<URL:http://www.psych.ndsu.nodak.edu/colloquia/colloq05fall/readings/jaco
bs.pdf>

Much later, full color vision was re-evolved again by an ancestor of the
Old World primates. This occurred after South America split from Africa
about 30 to 40 million years ago, so that while Old World primates are
trichromatic, their New World primate cousins are dichromatic.

How did evolution from dichromatic to trichromatic vision actually
occur? By gene duplication. One of the original two genes that codes
for proteins called opsins in the cones of the retina was duplicated.
Then the duplicate and the original gene evolved under selection to
respond separately to red and green light.

It's an interesting topic.


--
Alias Ernest Major

.

Relevant Pages

  • Most mammals evolved to be color blind
    ... mammals are dichromatic and are red-green color blind. ... "All apes and Old World monkeys have trichromatic vision, which allows them to see across the visible spectrum from blue to green to red. ... Most other mammals are dichromats -- they can see blue and yellow hues but cannot perceive or distinguish red from green." ... Whales and dolphins are monochromats -- they have no color vision at all. ...
    (talk.origins)
  • Re: Most mammals evolved to be color blind
    ... Whales and dolphins are monochromats -- they have no color vision at all. ... By gene duplication. ... They also have a variety of opsins with different color sensitivities. ...
    (talk.origins)
  • Re: Why are blue cones rare in humans?
    ... Color vision is interesting. ... It turns out that mammals ... Primates are nearly all diurnal, ... which lack colour vision. ...
    (sci.anthropology.paleo)
  • Re: Most mammals evolved to be color blind
    ... "All apes and Old World (African and Asian) monkeys have trichromatic ... Whales and dolphins are monochromats -- they have no color vision at all. ... vertebrate ancestor of fish, birds, reptiles and mammals. ...
    (talk.origins)
  • Re: Most mammals evolved to be color blind
    ... Whales and dolphins are monochromats -- they have no color vision at all. ... I hesitate to agree that genes for colour vision are conserved ... birds, and primates from whales. ...
    (talk.origins)