Science Questions

Is there a metabolic cost to the generation of bright colours in animals?

Sun, 4th May 2008

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Gary Stab asked:

Is there a metabolic cost to the generation of bright colours in animals?


Itís a very good question and youĎre absolutely right and there are pigments that animals use to attract mates. Thatís generally what itís all about. These are molecules that are quite costly to create. Not to mention the fact that you also look more obvious to things like predators. This was a question that someone, a guy called Geoffrey Hill looked at. Heís from the University in Alabama. He looked at house finches that grow colourful feathers in yellows and orange and reds using carotenoid pigments. Similar to what Dave was talking about earlier. What he did was he actually fed a bunch of house finches with these types of pigments in water. He fed half of these birds lots of food so they were nice and happy and were doing great. The other half he restricted their diets, which wasnít very nice. Basically he wanted to know what the difference was when they did and didnít have enough food to eat. As you might imagine, the ones that didnít get enough food were much more drab than the ones that had lots of food who grew lots of night, shiny colourful feathers. Thatís a really good way of showing to us that yes, producing pigments is expensive in food and if you havenít got enough food to do that then you tend to not be able to produce such brightly coloured feathers.


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Gary Staab asked the Naked Scientists: It there a metabolic cost to the generation of bright colours on certain animals? Some birds for instance have brighter breeding colours. Thanks for any help you can give. regards, Gary What do you think? Gary Staab, Fri, 25th Apr 2008

Can't see why there would be.  There may be a risk in some case in higher predation (rather depends on the animal - in many species, bright colours are a warning of poison, and so may help against predation).

If the colour is a warning of toxins, then I would guess the toxins would probably have a metabolic cost; and it is conceivable that certain particular cases of bright colours might be indicative of a more complex process that has a cost.

Bear in mind that what may seem bright in the visual spectrum on one animal, may not be visible at all as a colour within the visual spectrum of another animal, since different species of animals can have very different ranges of colour they are able to see. another_someone, Fri, 25th Apr 2008

I suspect that there would be, although it probably depends on how the bright colors are created. Bright colors in some animals are due to pigments, whereas others are due to certain optical effects caused by microstructures (as in certain butterflies). In birds, both forms are known.

If the pigment needs to be created by the bird's metabolism, then cellular machinery that was inactive or less active in the nonbreeding phase would need to become more active during the breeding phase. This would require some expenditure of energy. On the other hand, carotenoid pigments can be obtained from a bird's diet (such as in the northern cardinal), which probably requires much less metabolic effort than generating pigments from scratch.

EDIT: Actually, I can think of a possible scenario where putting on breeding colors would be less expensive metabolically than having their normal coloration. I don't know if this is the case in any species, but it seems plausible. Let's say that a bird is normally green due to a combination of yellow pigmentation and blue iridescence (due to the microstructures I mentioned earlier). Let's also say that the breeding color of this particular bird is blue. In order to achieve that color, all it would have to do is stop producing yellow pigment. All that's left would be the blue iridescence. Hence, a lack of pigment could produce new coloration. Supercryptid, Fri, 25th Apr 2008

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