Thursday, March 10, 2011

Evolution, Why So Blue?--An Idle Speculation on Coloration

Seed question that propagated this blog:  Why are some skink tails blue?

Then, the questions kept rolling in:
  • Why is blue a relatively rare color in nature?  Is it actually rare?  What percentage of different clades like flowers, reptiles, birds, etc. are blue?
  • Is blue the anti-red/orange?
  • Could it actually be to attract predators to its tail (so as to distract from its body/head) much like false eye spots/false heads?
  • Does it serve a mating purpose?
  • Why do some of the same species of skink have red or pink tails?
  • Does the skink's tail detach?  Would a predator attacking its tail as opposed to its body actually make it more likely to survive?
  • Is sight an important sense for the important predators of the skink?  What are the main predators?  Is there variation in coloration in areas that have more of a certain kind of predator?
  • Are the pigments that create blue difficult to evolve or metabolically costly to make?
Hypothesis Number One: Blue is the anti-red/orange.  Meaning it functions as the opposite of a warning color.

You may be well aware that many species use the bright red/orange coloration to advertise themselves as poisonous, venomous or foully flavored.  It's literally a bold move, but for many, many organisms it's a great way to avoid getting eaten.

So, why on earth would you do the opposite of that warning coloration and essentially advertise that you're edible?  It seems suicidal, but there may be strategy in it yet.  First, consider some other animals that do something sort of similar:

False Eye Spots (so a predator goes toward the end that you're best at getting away from and that is the least vital to survival):

False head Tails:

I've even seen video where this guy (or perhaps a similar species) will move their wings up and down to create a motion with the false antennae that is picture perfect of the real deal. 

How we could test to see what the purpose of the tail really is:
  • Paint the tails other colors such as red or the normal color of the skinks body and observe
    • Differentiation of mating success
    • Differentiation of death by predation
  • Find out predator distribution and abundance in areas that have color variations such as red or pink.
  • Test the break-ability of the tail during predator attacks to see if attracting predators toward tail and away from body/head is actually effective or not.
  • Count the number of broken/attacked tails in a normal population in comparison to comparable lizard species to in comparison to skinks with variant tail colorations to determine if the tails does in fact serve as a escape mechanism.

Second hypothesis: Blue is the anti-red/orange for mating displays.  Blue is dangerous since it is the opposite of a warning coloration and therefore red would more likely be used first, but once red/orange is taken subsequent species will want to contrast themselves to avoid inbreeding and watering down their evolved adaptations.

Is it just coincidence that blue footed boobies and the red decorated frigate bird nest on the same islands?

How we could test it:
  • See if there areas that have blue species but no red species
  • Count and establish the coloration break down as percentages
  • In areas that there is variation or even reversal of coloration establish population sizes of both contrast species as well as the significance of predation.
  • Genetically trace the age of species and see if blue species or red species split first from a common ancestor.

Their hypothesis:  Blue is the anti-red/orange for displays in flowers.
  • Same as above.
Hypothesis Meltdowns?

Images are from here, here, here, here, here, here, here, here, here, here, here, herehere, here and here.

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