I have detected James' draft post on shrimp circularly polarised light detection: I have a National Geographic at home which says a particular species of shrimp can detect something around 21 wavelengths/polarisations of light. Quite impressive...

Another group from BIOL1040 that I asked questions of had found research on the different spectra that primates can detect. Humans are generally trichormats (3 frequencies + rods), as are most Old World primates (and most marsupials) whereas except for Howler Monkeys, New World primates and most other mammals are dichromats (2 frequencies + rods). The interesting bit about New World primates is that their gene structure allows females to be trichromats whilst males are dichromats. This occurs because the gene for red and green colour sensing (blue/violet apparently was the first type to develop) occupies the same locus (i.e. spot) on the NW primate X-chromosome, so females can have both genes (one on each X chromosome) and are trichormats (unless they recessively possess only the same gene on both X chromosomes) but males can only ever possess one of the genes (on their single X chromosome). Howler monkeys are thought to have re-developed trichromatic vision from gene duplication; apparently mammals in dinosaur times were tetrachromats (could see 4 colours). The evolutionary reason for this unusual set-up in NW primates was suggested to be that darker conditions favour dichromatism (it's better in low light conditions, apparently) whereas in lighter conditions, trichromatism is more useful (you can tell the differences between fruits, for example, or between paintings, local creatures of the Amazon)—communities of primates of one species can therefore utilise all of the members' vision ranges to the group's advantage. I was a little skeptical about this point, however, as I don't really see why trichromatism is a disadvantage in low light conditions; surely low light sensitivity is more dependent on rods and eye structure?

An analysis of the wavelengths of the opsin pigments would be interesting. I must also remember to post another BIOL1040 response on eye structure and detection pigments (e.g. opsin) in cubozoans (i.e. box jellyfish) compared with other lineages (e.g. vertebrates).

Other interesting visual patterns include lungfish, which see four wavelengths, bees, which see UV, green and blue, and many bird species in which juvenile members see four wavelengths but adults only see three or two.

Then there are crustaceans....

Also, an interesting thing I read in a Scientific American concerned the human brain's way of interpreting colours. Apparently, we see in a blue-yellow channel and a green-red channel, preculding the existence of greeny-reds and bluey-yellows. Unless you torture a subject's poor brain for some time. I may have to search for the issue, I read it in a doctor's surgery some time ago....