Bluff- and baffle-displays in lizards, part 2: Chlamydosaurus, Callisaurus

(writing in progress)

...continued from https://www.inaturalist.org/journal/milewski/68250-bluff-and-baffle-displays-in-lizards-part-1-several-overlooked-aspects-of-the-aberrant-skink-tiliqua-rugosa#

Wikipedia on deimatic behaviour = startle displays, with particular reference to lizards:
 
The following review in Wikipedia of startle behaviour (deimatic behaviour) http://en.wikipedia.org/wiki/Deimatic_behaviour
is a pleasant surprise. I note that it gives the Australian frill-necked lizard (Chlamydosaurus) as a classic example of a deimatic display in lizards, and I’d agree with that. However, it makes no mention of Australia as a place where deimatic behaviour is taken to extremes by lizards.
 
An overlooked point is that morphologically specialised deimatic displays, although common among Australian lizards and taken for granted by both herpetologists and the lay person in Australian lizards, are actually rare anywhere else in the world, the only other prominent example being the bluff so familiar in chameleons.
 
The difference, I suggest, is that chameleons don’t actually have body parts devoted exclusively to deimatic (anti-predator) displays. The colour inside their mouth is not particularly lurid, and I think the hissing and flattening of the body and swaying are used in intraspecific antagonism as well as in anti-predator bluff. What we’re looking for in the lizards of the world is deimatic displays that have special morphological features evolved to support them. The frill-necked lizard does use its frill intraspecifically but I’d argue that such an extreme modification (which necessitates an actual lengthening of the neck skeleton to accommodate the frill) did not evolve mainly as an intraspecific adaptation, but is instead mainly an anti-predator adaptation which is then used intraspecifically as well. Important in my rationale is that there is no sexual dimorphism (this does need checking as a fact) in the size or shape of the frill in Chlamydosaurus.
 
The North American iguanid Phrynosoma does squirt blood from the corner of its eyes, which is deimatic bluff, but the anatomical modifications involved (in the vascular system of the eyelids/orbits) are not in themselves visible to a predator. This is rather different from the huge ‘beard’ of the Australian agamid Pogona barbata, the huge frill of the Australian agamid Chlamydosaurus kingii, the fleshy tongues of sundry Australian skinks and pyogopodids, the lurid colours inside the mouths of the Australian  Tiliqua and related large skinks, and even the pied whole-body colouration of Bell’s form of Varanus varius.
 
Have I overlooked some other group of lizards on another continent that does show clear morphologically-based deimatic behaviour after all?

Type of sexual dimorphism in frill-necked lizard chlamydosaurus indicates that frill evolved for interspecific rather than intraspecific displays: 
 
I cite the case of the frill-necked lizard (Agamidae: Chlamydosaurus kingii) as an example of how Australian lizards have evolved morphological features specialised for bluff-displays against potential predators. Since the Wikipedia site for this species mentions that the frill is also erected in ‘territorial’ displays, someone might suggest that the original evolution of the frill was intraspecific (i.e. social) and that the anti-predator application is a corollary or epiphenomenon of that. I don’t think so, for the following reason. Chlamydosaurus is indeed sexually dimorphic, but the difference – while great – seems to be purely in overall body size, NOT in either the development of the frill or in colouration. Since the females are as encumbered as the males by the frill (which requires this lizard to have a remarkably long neck by the standards of an agamid, and indeed a lizard in general), and there is sexual dimorphism, the logical conclusion is that the frill has not been evolved by sexual or social selection. I’ve never seen this distinction discussed in the literature on this species.
 
http://en.wikipedia.org/wiki/Frill-necked_lizard

Zebra-tailed lizard of North American semi-desert has threat display lacking morphological specialisations for anti-predator bluff
 
The zebra-tailed lizard (Callisaurus draconoides) lives in the semi-deserts of North America, particularly in creosotebush (Larrea) flats.

This is a fast-running, diurnal lizard.

Callisaurus belongs to the Phrynosomatidae, which is the local equivalent of fast-running agamids in Australia.

Here is a good series of photos illustrating this species: http://www.californiaherps.com/lizards/pages/c.d.rhodostictus.html .
 
Please see http://www.californiaherps.com/lizards/images/cdraconoidesnvdw807.jpg. This threat display seems, at first glance, to emulate the kind of bluff seen in various Australian lizards. However, I do not think that this lizard displays to predators in this way, and I suspect that this photo was of a male displaying to another male, i.e. social = intraspecific antagonism.
 
Please see http://en.wikipedia.org/wiki/Zebra-tailed_lizard#mediaviewer/File:ZebraTailed-Lizard-640px.jpg.
This shows a normal posture in this lizard, in which it raises its conspicuously barred tail to advertise the tail, possibly as a distraction to raptors from the vulnerable head. The tail can be lost in an attack survived by the lizard, which is a common ploy among lizards.
 
The dull-orange dewlap in the threat-displaying male below may seem to be analogous with the morphological specialisations I have pointed out in sundry Australian lizards, for interspecific (= anti-predator) bluff, but I do not think that’s the case. I think this is a male feature used exclusively in a social = intraspecific way.
 
The difference between this lizard and the syndrome I have described in Australia is that the zebra-tailed lizard depends on a combination of speed and distraction, rather than standing its ground and bluffing.

I think the whole strategy vs predators is different. The Australian lizards I refer to are relatively slow-moving and inconspicuously coloured until they display against predators, whereas this North American lizard is not particularly inconspicuous because it tends to move rapidly in its normal foraging behaviour.

I document this example here because I see this as one of the reasons why the Australian focus of the bluff strategy has hidden in plain sight, overlooked by herpetologists.
 
The North American genus that squirts blood from the corner of its eyes, which certainly is a bluff display because the blood is harmless, belongs to the same family, Phyronosomatidae. That genus might marginally qualify as analogous to the Australian pattern I refer to, of reliance on and morphological specialisation for bluff.

However, I do not think the zebra-tailed lizard qualifies at all, despite the fact that it does have markings and physical structures in its body that advertise it as opposed to hiding it.
 
(writing in progress)

Posted on Ιούλιος 31, 2022 0756 ΜΜ by milewski