A photo-guide to the bewilderingly complex colouration of the South African rock-dwelling agamid, Agama atra, part 2: Discussion

...continued from https://www.inaturalist.org/journal/milewski/86633-a-photo-guide-to-the-bewilderingly-complex-colouration-of-the-south-african-rock-dwelling-agamid-agama-atra-part-1#

DISCUSSION

Thermoregulation:

There is a puzzle w.r.t. pallor, in the photos shown above. This is that the dates and times of day do not suggest high temperatures.

Inferring age and stage of development from photos:

The stage of development, from infancy (https://www.inaturalist.org/observations/21258571 and https://www.inaturalist.org/observations/45588229 and https://www.inaturalist.org/observations/41674366 and https://www.inaturalist.org/observations/39396548) to maturity, is apparent from the proportional size of the head.

In full maturity, females differ from males in having

• a somewhat smaller head, proportional to the rest of the figure (fully mature female: https://www.inaturalist.org/observations/63493740 ; mature male https://www.inaturalist.org/observations/62382011),
• an obviously swollen torso when in breeding condition, and
• a tail that is less muscular at the base (https://www.inaturalist.org/observations/63968894), and cylindrical as opposed to laterally compressed.

The sexual difference in the proportional (and absolute) size of the head is shown, within a single photo, in https://www.inaturalist.org/observations/61860075.

Infants and small juveniles have camouflage-colouration (https://www.inaturalist.org/observations/62613810). They are conspicuous only when they darken on a pale background (to bask), or show pallor on a dark background (presumably to cool down).

Even adult males remain capable of full camouflage, at least when not in breeding condition (https://www.inaturalist.org/observations/69668035).

In large juveniles of both sexes, the head and forelegs start to turn blue.

There is a sexual difference in the mottled pattern on the torso, which - although subtle - is so basic that it seems to appear just after infancy. In females of all ages, the mottling tends

• to obscure any vertebral striping, and
• to coalesce into a series of parenthesis-like markings, which are dark and dull in non-breeding condition and orangeish in breeding condition (https://www.inaturalist.org/observations/99528405 and https://www.inaturalist.org/observations/144070129).

By contrast, in males,

• the pale vertebral stripe tends to override mottling on the mid-dorsal line,
• there is no parenthesis-like coalescence of the mottling on the torso,
• mottling tends to become converted to faint pale spotting (https://www.inaturalist.org/observations/20536014), and
• all mottling/spotting tends to become obscure with age and breeding condition.

In partial summary, adult females have a distinctive pattern of coalesced mottling on the torso (https://www.inaturalist.org/observations/21294558 and https://www.inaturalist.org/observations/65326350). This pattern is not seen in males, which instead tend to feature a pale vertebral stripe (https://www.inaturalist.org/observations/65263707).

This difference transcends the conspicuous colouration of breeding condition.

Yellow on the torso (https://www.inaturalist.org/observations/56830136 and https://www.inaturalist.org/observations/64351861) is exclusive to females. However, it is not a reliable clue, because it

• appears only in breeding condition,
• is individually variable,
• is somewhat subject to emotional dimming, and
• is most reliable on the abdomen just anterior to the hindleg (https://www.inaturalist.org/observations/101547517 andhttps://www.inaturalist.org/observations/63977372 and https://www.inaturalist.org/observations/63949674 and https://www.inaturalist.org/observations/62048748), where it tends to be hidden by posture and perspective.

The following individual adult female (https://www.inaturalist.org/observations/63147613) is unusual in having

• a distinct pale vertebral stripe, and
• extensive bluish hue.

A nuance of colouration in the southern rock agama:
In adult females in breeding condition, the yellowish hue on the abdomen (https://www.inaturalist.org/observations/133489094 and https://www.inaturalist.org/observations/66135312) is less subject to dimming than is the bluish hue on the head.

This makes sense, because the yellowish has an anatomical position more easily hidden by posture and perspective (https://www.inaturalist.org/observations/65650375 and https://www.inaturalist.org/observations/64931512).

Ultimately, the most reliable clues distinguishing female from male, and immature from mature, are subtle. In the following view of an individual adult female (https://www.inaturalist.org/observations/102309969), the best clue to sex is the pattern of reddish-brown mottling on the torso, and the best clue to maturity is the size of the head relative to the rest of the figure.

No subspecies seem to be recognised in the southern rock agama. Populations in Namaqualand and Namibia are distinctive in their large body size and continual, as opposed to seasonal, reproduction (https://www.ajol.info/index.php/az/article/view/154319 and https://www.tandfonline.com/doi/abs/10.1080/15627020.2000.11657095).

Is it possible that this species is colour-polymorphic w.r.t. masculine colouration?

What I have noticed is as follows:

The first hypothetical colour-morph lacks all hues other than blue/turquoise, and is conspicuous partly by means of dark/pale contrast, with a dark torso and tail, offset by a pale vertebral stripe (https://www.inaturalist.org/observations/179396975). Some individuals in this morph become suffused with blue/turquoise over the whole figure (https://www.inaturalist.org/observations/11080759).

The second hypothetical colour-morph features hues other than blue/turquoise (https://www.inaturalist.org/observations/18556540 and https://www.inaturalist.org/observations/18814684 and https://www.inaturalist.org/observations/99620263 and https://www.inaturalist.org/observations/9132995 and https://www.inaturalist.org/observations/1155363).

I refer particularly to yellowish on the tail (https://www.inaturalist.org/observations/10833032 and https://www.inaturalist.org/observations/11100269 and https://www.inaturalist.org/observations/65534572 and https://www.inaturalist.org/observations/11123055 and https://www.inaturalist.org/observations/11079497) and reddish on the abdomen and anterior surface of the upper hindleg (https://www.inaturalist.org/observations/135283106).

This morph lacks dark-pale contrast, and the yellowish on the tail is precocial (https://www.inaturalist.org/observations/11019855).

In preparation of this Post, I thrice-examined each of the 5,300 observations (>6,000 photos) of the southern rock agama in iNaturalist, learning more with each of my three consecutive bouts of scrutiny.

After this 10-day effort, much remains obscure/confusing to me. For example, both sexes, plus well-grown juveniles, can feature blue/bluish on the head, while at the same time this hue is inconsistent in all these categories.

One of the few clear findings is that yellowish on the torso is completely diagnostic of femininity (https://www.inaturalist.org/observations/11113700) in this species of lizard. However, even this falls short of being categorical, because yellowish is not apparent in some views of full feminine colouration (https://www.inaturalist.org/observations/1577168).

Publicado el 15 de noviembre de 2023 a las 01:12 AM por milewski