Monkey see (colors), Monkey do (was RE: Marsupials see colors)

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> T. Michael Keesey
>
> On 3/27/06, Guy Leahy <xrciseguy@sbcglobal.net> wrote:
> > This is interesting... This would appear to knock more
> > holed in the hypothesis that black and white vision is
> > predominant in mammals because they started out as
> > nocturnal animals in order to avoid competition with
> > dinosaurs (who were hypothesized to be primarily
> > diurnal, although that might not be true, either.)
> 
> It looks like only one marsupial species has been investigated:
> _Sminthopsis crassicaudata_, the Fat-Tailed Dunnart. Isn't it also
> possible that trichromacy is a synapomorphy of some metatherian
> subclade that includes _S. crassicaudata_?

Apparently in honey possums and wallabies, too.

> After all, trichromacy
> evolved at least twice among placentals (platyrrhine and catarrhine
> simians).

If only it were that simple...

The following is discussed in "The Howler Monkey's Tale" by Dawkins & Wong in 
Dawkins' _The Ancestor's Tale_ (and refs therein).

New World monkeys have odd sex-linked trichromatism (distinct from human 
sex-linked color-blindness: male color-blind humans are genetically 
trichromatic, apparently, but one of their opsins doesn't operate correctly).

Blue opsin genes are present in both sexes, and are not sex-linked. Red and 
green opsins are on the X chromosome.

So a male will have blue and either red or green. And females have blue and one 
of the following: only red, only green, or red and green.

And that's merely for the presence of the gene: not whether it's activated or 
not! But assuming both copies are active, any population of New World monkeys 
contains:

RB males
BG males
RB females
BG females
RBG females

In howlers, a gene duplication and/or translocation has resulted with both R & 
G on X, making them trichromats.

                Thomas R. Holtz, Jr.
        Senior Lecturer, Vertebrate Paleontology
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
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