UPDATE - Another paper by Stuart-Fox et al. that appeared shortly after the work on social color change shows that chameleons do indeed change color in response to predators to increase their crypsis. Specifically, this paper shows that the dwarf chameleon (Bradypodion taeniabronchum) exhibits different responses to snake and bird predators, and does so in a manner that likely optimizes its camouflage in each case. As much as I hate to admit it, chameleons are obviously much better at this whole color change thing than anoles... [Thanks to commenter Michael Meadon for pointing this out]Ask anybody why a chameleon changes its colors and you're sure to hear something about it trying to blend in with it's background. It may come as a surprise to many of you, then, that this simply isn't true. Chameleons, and most other reptiles that are into color change (e.g., Anolis carolinensis, a.k.a. "the American Chameleon"), do so almost exclusively for social reasons. Stuart-Fox and Moussali drove the nail in the coffin of this myth with a remarkable series of studies a few months back (one in American Naturalist and another in PLoS Biology). By combining data about chameleon color, the light environment in which they're displaying, and the visual systems of both chameleons and their potential predators, they were able to show that the conspicuous color-changes observed in the South African dwarf chameleon are specifically designed to stand out against their background for the purpose of social interaction. Got it? Color change in chameleons didn't evolve so that they could blend in with their background, but so that they could stand out against it! Of course, this doesn't change the fact that chameleons are still pretty damned good at being cryptic, just that the color change isn't used for this purpose.
PS - I couldn't agree more with their assertion "that quantifying signal conspicuousness to different receivers can be used to gain insights into the evolution of signal diversity in animals." In lizards, this type of work has been made possible to the remarkably thorough studies of Leo Fleishman and colleages, who have painstakingly measuring the properties of lizard visual system. Although the models remain imperfect, they're a hell of a start. Thanks Leo!
9 comments:
This is going to change our whole vernacular. We'll have to start calling those folks who try hard to stand out by wearing crazy clothes - chameleons!
Once again...beautiful proof that humans really don't rule the world.
...and here's a figurine to prove who does.
"Oh Britney, you're such a chameleon." I love it. Unfortunately, my last attempt to introduce obscure scientific jargon into the vernacular was a stunning failure. People just got confused when I called them a "cloaca."
Cool blog Rich et al. I look forward to reading future posts!
Ummmmmm... "Predator-specific camouflage in chameleons":
"A crucial problem for most animals is how to deal with multiple types of predator, which differ in their sensory capabilities and methods of prey detection. For animals capable of rapid colour change, one potential strategy is to change their appearance in relation to the threat posed by different predators. Here, we show that the dwarf chameleon, Bradypodion taeniabronchum, exhibits different colour responses to two predators that differ in their visual capabilities. Using a model of animal colour perception to gain a ‘predator's eye view’, we show that chameleons showed better background colour matching in response to birds than snakes, yet they appear significantly more camouflaged to the snake visual system because snakes have poorer colour discrimination."
Also, as I read it, the PLoS paper argued that the ability to change color evolved as a result of social signaling. But then you argue that means chameleons never change their color to camouflage themselves. Clearly, that does not follow: the ability may have evolved for social signalling, and then be exapted for camouflage.
@Michael
Thanks for pointing this research out, I hadn't come across the Biology Letters paper previously. I obviously over-extended my interpretation of the PNAS and Am. Nat. work (based partly on my anole bias, which led me to believe that color change is rarely done for the purpose of improving camouflage).
Thanks for the correction... (You've got to love scientists. They quickly and graciously change their opinion when presented with new evidence; even if they don't really want to). :-)
Anyway, I've blogged about this: http://ionian-enchantment.blogspot.com/2009/09/chameleons-do-change-their-color-to.html
(My tone is a touch harsh -- I wrote most of it before I saw your correction, and I was rather annoyed by the Cracked piece I linked to).
Who's the predator here?
http://www.youtube.com/watch?v=KMT1FLzEn9I
How do you explain this?
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