Male and female phenotypes of the southern rock agama (𝘈𝘨𝘢𝘮𝘢 𝘢𝘵𝘳𝘢)
Many lay people are under the impression that only the males of the southern rock agama (𝘈𝘨𝘢𝘮𝘢 𝘢𝘵𝘳𝘢) develop blue heads. The truth is that both the males and the females develop blue heads during the breeding season. But how do you then tell the males and females apart?
Bearing in mind that agamas can subdue their bright colours fairly quickly if they feel threatened and also that the specific characteristics are not absolute and can vary in their extent (sometimes being absent), the following can serve as a guide regarding the breeding colouration:
Males:
• Streak of blue or purple on the side near the belly behind the front legs (never seen in females).
• Reddish area in front of the back legs.
• Fairly uniform colouration on the back (ranging from brick red to bluish grey, sometimes almost
black), but with some lighter small spots and markings of a slightly different hue.
• Tail has some colour on the sides, usually yellow, but blue to bluish-green in some populations.
Females:
• Yellow "blush" on the rump near the back legs, but often extending further forward, sometimes over
the entire rump/torso area (males never have this yellow blush).
• Greyish background where the yellow blush don't reach.
• Rust-coloured markings on the body, contrasting strongly with the yellow or grey background (the
pattern of these markings correspond somewhat to those in males, but in males they are a similar
colour to the background and thus don't stand out much).
• Tail doesn’t have any colour.
There are also some other physical aspects that may differ between the sexes, although again it is not absolute:
Males:
• Generally larger in overall size.
• Jawline is often slightly broader.
• Tail is usually better developed, slightly flattened laterally but generally more bulky, sometimes with a
little crest of larger scales running down the middle.
Females:
• Generally smaller in overall size.
• Jawline is often slightly narrower.
• Tail is usually less well developed, rounder in cross-section, thinner and sometimes shorter. No crest.
Some breeding pairs:
https://www.inaturalist.org/observations/139408521
https://www.inaturalist.org/observations/67563782
https://www.inaturalist.org/observations/61860075
https://www.inaturalist.org/observations/191175877
Some males:
https://www.inaturalist.org/observations/190412280
https://www.inaturalist.org/observations/97986502
https://www.inaturalist.org/observations/61211970
https://www.inaturalist.org/observations/147831154
https://www.inaturalist.org/observations/184891185
https://www.inaturalist.org/observations/9228425
https://www.inaturalist.org/observations/143025666
https://www.inaturalist.org/observations/188709545
https://www.inaturalist.org/observations/101385982
https://www.inaturalist.org/observations/152609597
https://www.inaturalist.org/observations/133324336
Some females:
https://www.inaturalist.org/observations/143645814
https://www.inaturalist.org/observations/146468039
https://www.inaturalist.org/observations/173464815
https://www.inaturalist.org/observations/144963903
https://www.inaturalist.org/observations/145416431
https://www.inaturalist.org/observations/104416131
https://www.inaturalist.org/observations/37026553
https://www.inaturalist.org/observations/189509923
Some of the female characteristics of 𝘈𝘨𝘢𝘮𝘢 𝘢𝘵𝘳𝘢 can also be seen in females of some other species of 𝘈𝘨𝘢𝘮𝘢.
Note the diminutive tails and contrasting rust-coloured patches in these female eastern ground agamas (𝘈𝘨𝘢𝘮𝘢 𝘢𝘤𝘶𝘭𝘦𝘢𝘵𝘢 𝘥𝘪𝘴𝘵𝘢𝘯𝘵𝘪):
https://www.inaturalist.org/observations/190557824
https://www.inaturalist.org/observations/143724380
https://www.inaturalist.org/observations/142544804
The females of Anchieta’s agama (Agama anchietae) and Bibron’s agama (Agama bibronii) can be a close match to the females of 𝘈𝘨𝘢𝘮𝘢 𝘢𝘵𝘳𝘢:
https://www.inaturalist.org/observations/10819713
https://www.inaturalist.org/observations/185586248
https://www.inaturalist.org/observations/167774913
https://www.inaturalist.org/observations/159708354
https://www.inaturalist.org/observations/148341047
https://www.inaturalist.org/observations/145327257
https://www.inaturalist.org/observations/121469067
Comments
@milewski
Many thanks for this much-needed guidance. This species is familiar to many naturalists in South Africa. Yet, scrolling through the thousands of photos on the Web feels like negotiating a labyrinth of several genera and spp., rather than a single entity. Your explanation sheds light on the patterns, and gives us clear search-images.
Do you think the following (https://www.inaturalist.org/observations/144402916) is a case of a) thermodynamic pallor or b) substrate-matching?
In the second photo in https://www.inaturalist.org/observations/143370440, male above and female below?
I have noticed that darkening of the torso seems to differ according to sex, among individuals in breeding condition.
In males in breeding condition, it seems that the torso is often dark, except for the pale vertebral stripe (e.g. https://www.inaturalist.org/observations/142171869).
In females, by contrast, the torso never seems to darken, and also never seems to feature a conspicuously pale vertebral stripe.
If I am right, then there is a basic difference in the conspicuousness of the torso in the two sexes.
In males, the boldness is mainly tonal as opposed to chromatic, i.e. it uses dark/pale as opposed to hue. There is a hint of reddish on the abdomen in males, but this a) is not bright-hued enough to be striking, and b) seems to be readily obscured by darkening.
In females, the boldness is strictly chromatic, i.e. it uses mainly yellowish and to a lesser degree orangeish hues.
An associated difference is that apprehensive dulling ('switching off') of the hues, when approached by a predator, does not produce camouflage in mature males, whereas it does so in females. This is basically because the torso of males loses its mottling in maturity, whereas that of females retains its mottling but merely converts this, in breeding condition, to a chromatically noticeable combination of yellowish ground-hue and orangeish markings.
https://www.dreamstime.com/southern-rock-agama-lizard-agama-atra-southern-rock-agama-lizard-agama-atra-its-blue-metallic-colered-head-image104639129
https://www.inaturalist.org/observations/135278582
Your thoughts?
"Do you think the following (https://www.inaturalist.org/observations/144402916) is a case of a) thermodynamic pallor or b) substrate-matching?"
If it is indeed one of the two it is more likely to be thermodynamic pallor because camouflage is already compromised by the blue head. It might also just be a lighter coloured individual.
"In the second photo in https://www.inaturalist.org/observations/143370440, male above and female below?"
Correct.
"An associated difference is that apprehensive dulling ('switching off') of the hues, when approached by a predator, does not produce camouflage in mature males, whereas it does so in females. This is basically because the torso of males loses its mottling in maturity, whereas that of females retains its mottling but merely converts this, in breeding condition, to a chromatically noticeable combination of yellowish ground-hue and orangeish markings.
Your thoughts?"
I would say that the dulling affords adequate camouflage to both sexes (although not perfect). But perhaps it could also be that dulling in males signals subordination more than being camouflage. I have to say that I'm merely guessing here.
Is these really Agama atra, as labelled ?
https://www.dreamstime.com/stock-photo-southern-rock-agama-lizard-namibia-africa-image68601433
https://www.dreamstime.com/male-southern-rock-agama-atra-bright-breeding-colors-namibia-image223921541
https://www.dreamstime.com/male-southern-rock-agama-agama-atra-bright-breeding-colors-namibia-male-southern-rock-agama-image284199653
@milewski yes I think these are all Agama atra. I am almost certain the top one was photographed in the Western Cape somewhere instead of Namibia. The bottom two could be assigned to Agama knobeli by some people, but knobeli is a problematic taxon. But the high-crested morph sometimes pop up in atra populations in many parts of its distribution. It might be more prevalent in parts of Namibia.
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