Dickerson’s collared lizards. Photo from http://www.herpnation.com/wp-content/uploads/2012/05/Dickersons-Collared-Lizard-Crotaphytus-dickersonae-700×466.jpg
What the heck gives with blue lizards? Collared lizards, geckos, lacertids, teids, anoles—there’s more blue lizards than you can shake a stick at. And they stand out like a sore thumb. How can they possibly survive? And in those species in which only the males are blue, do the lady lizards really have an azure fixation?
Male Anolis allisoni from Atkins Botanical Garden, Cienfuegos, Cuba. Photo by J. Losos.
Male Anolis allisoni from Cuba are famous as the day-glo green lizard with a blue jumper. But their Honduran descendants are much less cerulean—indeed, here on Roatan, they barely have a hint of the cobalt (see below). What’s going on? It would seem that whatever has favored blueness in Cuba is not favoring it here. Do the ladies out here swoon not as much for indigo? Are the predators tougher? Is the environment different? Who knows. And has the population here reached a new, less blue, stable-state, or is it in the process of losing its turquoise entirely, returning to its verdant roots. At this point, we don’t have a good time estimate for how long allisoni has been here—if it’s a recent arrival, it would certainly be a reasonable hypothesis that the blue wash is on its way out entirely.
Male Anolis allisoni from Roatan. Photo by J. Losos
See if you can spot the lizard.
But while we’re on the topic of color craziness, here’s another question: how come green anoles can’t—or don’t—match their background? Color mavens may be offended at my non-analytic assertions, but I insist that green anoles often are conspicuous. On white tree trunks (much less brown or red ones), a green anole stands out a mile away.
How about this one?
Sure, green’s great for camouflage when you’re in the vegetation, but if you could change colors, wouldn’t you do so when on non-green backgrounds. Octopi can do it, why not anoles? Or, at least, why don’t they stay on green surfaces when they don’t want to be detected. Although, truth be told, not all greens are the same, and the bright green of these species often stands out against darker green vegetation (check out the anole in the grass in yesterday’s post, reprinted to the left).
Green lizard in the grass: not so cryptic
Now, some contrarians may claim that they’re actually trying to be conspicuous—Bob Trivers, for one, suggested that the beautiful green A. garmani intentionally perched in conspicuous sites in order to be seen. Maybe that’s so, but most of the time, anoles don’t seem like they’re trying to be seen, especially the females. And, yet, you can’t miss them.
Finally, of course, I have to acknowledge that it’s possible that I failed to spot one or two green anoles in green vegetation, especially high in trees. So, it may be that green is the color that camouflages them most effectively. Still, they could do better by changing color to match where they’re sitting, or by only sitting where they don’t stand out.
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Ted
I had a student on Roatan some many years back, her name was Allison. I found one of these beasts for her and encouraged her to capture it. When she did, she asked me what its name was and when I told her she thought I was making it up-very funny and I bet she never forgets it’s name.
Manuel Leal
The elusive mystery of background matching continues.
Leo Fleishman
We’ve been working on some experiments that suggest that it is not critical to match the specific background you are sitting on. You can think of the whole visual field as a broad area filled with discrete patches of color. We hypothesize that to avoid being noticed an animal’s color should be similar to other common natural patches of colors in the visual field. If you (the observer) are actively searching for a lizard, or if one moved and caught your attention, it may seem very easy to see. However if it’s out there in your visual periphery, and it matches other patches of color, you might never notice it. We have some preliminary lab and field data that supports this. This can obviously explain green or brown patterns, and perhaps blue as well (patches of sunlight). More when the results come in!
Peter Mudde
You should keep in mind that the most obvious predators, birds, snakes and larger lizards have a rather different perception of color then we have. Our kind of perception for colors is rather rare in nature and found mainly in primates.. It looks rather possible to me that the shades of green and blue that seem to stand out are much less standing out in ultraviolet. Maybe there is someone who has the equipment to test this…
James Stroud
Great post on a really interesting subject! In terms of blue colouration, some of Roger Thorpe’s work on Gallotia galloti may seem relevant here? Blue cheek and body patches were shown to highly reflect UV and were surrounded by areas of non-reflective skin. This is hypothesised to be an important factor in visual communication in this species, although it didn’t effect female mate choice. Variation in patch size and positioning changes with habitat type across the Tenerife ecotone (in the Canary Islands).
A good book chapter on the subject can be found here: http://www.uv.es/fon/Font%26Molina-Borja2004.pdf
I wonder if readers of Anole Annals can post if similar research has been conducted on the importance of blue colouration in terms of UV reflectance in A. allisoni? (I only know of studies on A. conspersus by Macedonia). It would seem A. allisoni would a perfect model species and system for a similar type of study…
Jerry Husak
Very interesting example here! Since you mention Crotaphytus dickersonae, I thought I’d point out work by Joe Macedonia (and colleagues) on that species. They looked at background ‘matching’ against various aspects of the surrounding environment using different visual systems (lizard, bird, visual snake) in their models. While the blue in that species is likely sexually selected, they suggested that the potential predation costs might be offset a little, tiny bit, maybe, when the blue males are viewed against a blue sky or the blue sea. ‘Sea-matching’ probably doesn’t factor in with A. allisoni color evolution, but the sky…? I dare not speculate!
http://ib.berkeley.edu/labs/mcguire/Macedonia%20et%20al.dickersonae.pdf
Joe Macedonia
Given that I’ve seen my name mentioned by several responders to this post, I will add just a few thoughts. As Jonathan pointed out, there certainly are a number of blue lizard species other than anoles. But why choose blue? Blue certainly is a rare color in terrestrial environments, so if you want stand out from the earth tones of most visual backgrounds, blue may be a good choice for achieving the necessary color contrast. In herps, a nicely chromatic blue color can be produced through the combination of (1) a reduction or removal of pteridine and carotenoid pigments in the upper (xanthophore) layer of the chromatophores, and (2) the presence or addition of a substantial base of melanin underneath the iridophores. I found the combination of these traits at work when comparing the UV/blue dewlap of Anolis conspersus to the orange dewlap its sister species Anolis grahami. This same iridophore/melanin density relationship was found by Diana Hews and Vanessa Quinn to underlie the blue abdominal coloration of Sceloporus undulatus consobrinus, and likely extends to the blue bodies of Anolis gorgonae, Crotaphytus dickersonae, Cnemidophorus lemniscatus, and many more species. As for the conspicuousness of a green-bodied anole perched on a brown or white tree trunk, this probably is no accident: anoles that possess green body coloration can mobilize melanin to turn brown (metachrosis) rather quickly. Most of us have observed this phenomenon when slowly approaching a green-bodied anole just a bit too close for its comfort. The simplest explanation may be, as Trivers suggested, that adult males remain green when perching on tree trunks for a good reason – they are advertising their presence to other males and to females. Such males may not be as conspicuous to predators, however, as they are to us. Whereas green leaves typically do not grow out of tree trunks, this may not be a consideration by anole predators, and green patches are ubiquitously interspersed with brown patches in most anole habitats. Leo Fleishman pointed out in a review paper twenty years ago that although distinguishing the body shape of an anole from the visual background may not a particularly difficult task for humans (due to the superior feature extraction abilities of our visual cortex), these abilities should not be attributed to other animals by default.
Joe Macedonia
Ooops – I apologize for all the italics. I must have left off the “>” from one of the “” markers that I used to italicize species names….