Color vision: what do other mammals see beyond the green end of the spectrum?

[John Salerno]

I'm reading a book that discusses how most mammals other than primates are dichromatic, which to some extent I already knew given the common assumption that dogs, for example, are "color blind." I understand that they aren't fully color blind, of course, but that they can see basically from blue to green in the visible spectrum (visible by humans, at least!).

 

But it got me wondering, do we have any idea what a dog (or any other dichromatic animal) sees when presented with an object that is, for example, orange or red? Does it appear black and white to them? If so, what's happening in the eye to cause this appearance? Or does it appear as some other color that they *can* see?

 

Thanks.

[Mr Skeptic]

No, it will appear as some color or another. To get a vague idea of what can be seen with two color receptors, take a paint program and just make several combinations of only two of the three colors. To get an even better idea, you'd need two colors that are more opposite each other, but that would be more complicated to do.

[Sisyphus]

Well, if it's only reflecting red light, then it would appear black, just like something that only reflects infrared appears to us.

 

However, an object that appears red to us is not necessarily a "red object" in the sense that it is only reflecting red light. That something is "really" one color is pretty rare, so the animal would interpret the color of the object based on the ratio of the stimulus of the color receptors it does have. Just like we do - pretty much everything around you is emitting infrared light, but we can't see it, so our perception of color is based only on what we can see.

 

And even that is easily confused. We interpret color based on the ratio of how stimulated our three different color receptors are. For example, green falls between blue and yellow in wavelength, so it stimulates our blue and yellow receptors to the same amount. Therefore we can't distinguish between green light and a mix of blue and yellow light. Similarly, all the colors that a bichromate could see would be mixes of two primary colors.

[John Salerno]

Thanks guys. Last night I also thought of maybe a simpler way to ask the question. Since many humans are color-blind in the same way as dogs and other mammals, I wonder what the answer would be if a color-blind person described what he/she saw when looking at an object which appears red to others. This seems like an easier way to get an idea than to ask a dog.

[Darwinsbulldog]

An excellent resource on animal vision is:-

 

Land, M. F. N., Nilsson, D.E. (2002). "ANIMAL EYES". Oxford, Oxford University Press. Needless to say, a google scholar search with the names of these two authors will produce a rich selection of papers on vision, as they are regarded as leaders in the filed.

 

There are also lots of journal articles about vision, colour vision, and so on...eg

 

 

Awata, H., M. Wakakuwa, et al. (2009). "Evolution of color vision in pierid butterflies: blue opsin duplication, ommatidial heterogeneity and eye regionalization in Colias erate." Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology 195(4): 401-408.

This paper documents the molecular organization of the eye of the Eastern Pale Clouded Yellow butterfly, Colias erate (Pieridae). We cloned four cDNAs encoding visual pigment opsins, corresponding to one ultraviolet, two blue and one long wavelength-absorbing visual pigments. Duplication of the blue visual pigment class occurs also in another pierid species, Pieris rapae, suggesting that blue duplication is a general feature in the family Pieridae. We localized the opsin mRNAs in the Colias retina by in situ hybridization. Among the nine photoreceptor cells in an ommatidium, R1-9, we found that R3-8 expressed the long wavelength class mRNA in all ommatidia. R1 and R2 expressed mRNAs of the short wavelength opsins in three fixed combinations, corresponding to three types of ommatidia. While the duplicated blue opsins in Pieris are separately expressed in two subsets of R1-2 photoreceptors, one blue sensitive and another violet sensitive, those of Colias appear to be always coexpressed.

 

Yokoyama, R. and S. Yokoyama (1990). "ISOLATION DNA SEQUENCE AND EVOLUTION OF A COLOR VISUAL PIGMENT GENE OF THE BLIND CAVE FISH ASTYANAX-FASCIATUS." Vision Research 30(6): 807-815.

Visual pigment genes have been isolated from a Mexican blind cave fish, Astyanax fasciatus. We report here the DNA sequence of these genes, which has 70% nucleotide similarity with both the human red and green pigment genes. This gene appears capable of encoding a functional protein and is probably responsible for the green-sensitive pigment found in the pineal organ of the blind cave fish (Tabata, 1982). The pattern of nucleotide substitutions most likely reflects functional adaptation of the visual pigment gene during the past 400 million years of fish evolution.

 

As you can see, blind cave fish are an interest of mine. So perhaps I should add some variety:-

 

Kevan, P., M. Giurfa, et al. (1996). "Why are there so many and so few white flowers?" Trends in Plant Science 1(8): 280-284.

This review and discussion, with 44 references, explores the possible mechanisms involved in insect detection of flowers that appear white to the human eye. Most of them reflect UV light which is picked up by UV receptors in the eye of a bee or other insect. However, evaluation of UV signals alone may not be helpful, or at least inaccurate, and an understanding of biological signalling requires a comprehensive understanding of sensory physiology and perceptual psychology. Recent research has show that honey bees have great difficulty in learning to associate food rewards with targets which appear white to them, i.e. the flowers are equally reflective across the bee's whole visual spectrum. Floral characteristics not related to colour may attract pollinators to such flowers.Though the world we see appears to be rich in white flowers, this is not the case for animals, such as insects, with ultraviolet (UV) receptors. In fact, flowers that appear white to insects are very rare. This phenomenon is analysed to highlight new discoveries in the mechanisms of insect vision that may have influenced the evolution of flower colour. This analysis reveals that an understanding of biological signalling requires a comprehensive understanding of sensory physiology and perceptual psychology. An evaluation of UV signals alone may not be helpful, as this can be as inaccurate as models based solely on the human visual system. Floral colours and their frequency in nature are interpreted from the more relevant perspective of insect colour vision.

 

Insects can see into the ultraviolet, and so what appears to us as a plain white flower looks very different to a bee or whatever. As the human-ape-monkey clades are primarily aboreal, we have good colour vision to distinguish fruits etc, but lousy smell compared to dogs. Dogs have great olfactory senses but their vision is not as good. We can only distinguish about 200-250 smells whereas dogs can distinguish millions. In both cases, loss of function was accompanied by [or rather due to] loss of genes.

[John Salerno]

Thanks for the resources!