Ctenophorus decresii ( Duméril and Bibron, 1837 )

Dong, Caroline M., Johnston, Greg R., Stuart-Fox, Devi, Moussalli, Adnan, Rankin, Katrina J. & McLean, Claire A., 2021, Elevation of Divergent Color Polymorphic and Monomorphic Lizard Lineages (Squamata: Agamidae) to Species Level, Ichthyology & Herpetology 109 (1), pp. 43-54 : 46-47

Ctenophorus decresii ( Duméril and Bibron, 1837)

Tawny Rock Dragon

Figures 1A–C , 4A–B , 5A

Grammatophora decresii ( Duméril and Bibron, 1837: 472–

474). Amphibolurus decresii ‘southern race’ ( Houston, 1974: 51). Ctenophorus decresii ‘southern lineage’ ( McLean et al., 2013:

52).

Types.— The original description was based on two syntypes, a male and a female, from L’Île de Decrès (Kangaroo Island) and registered as MNHN 6545 ( Duméril and Bibron, 1837). We designate the male as lectotype (MNHN 6545; Fig. 5A ) and the female as paralectotype (MNHN 6545A; Fig. S2 ; see Data Accessibility) because only the male exhibits the diagnostic coloration .

Diagnosis.— Ctenophorus decresii is a member of the C. decresii species group ( Houston, 1974; Houston and Hutchinson, 1998). Within the C. decresii species group, C. decresii is distinguishable by the following combination of characters: snout scales smooth to longitudinally keeled; vertebral scales flat; presence of a broad dark undulating lateral stripe, often constricted into blotches and interrupted to form two separate blotches posterior to the tympanum; and in males, the throat is blue or blue and yellow with yellow to orange margins.

Description.— A moderately sized lizard reaching a maximum SVL of approximately 88 mm and total length of 230 mm. Head and body depressed. Tail long and tapered to a fine tip. Forelimbs moderately long, almost reaching groin when adpressed. Hindlimbs long and reaching or almost reaching snout when adpressed. Finger lengths: 4. 3. 5. 2. 1; toe lengths: 4. 3. 5. 2. 1. Characteristic of the genus, a distinct row of enlarged keeled scales extending from the nostril, below the eye to above the tympanum ( Houston and Hutchinson, 1998). Ear membranes exposed and scale-free. Scales on snout are smooth to longitudinally keeled. 12–18 supralabial scales; 11–16 infralabial scales; 4–6 scales between rostral and nasal; 4–6 scales between supralabial and nasal; 10–13 internasal scales; 21–29 subdigital lamellae on the fourth toe ( McLean et al., 2013). Dorsal crest is small, no more than a series of keeled scales, becoming smaller posteriorly and not reaching base of tail. Nuchal crest low or absent. Scales on the dorsal surfaces of the limbs and tail are keeled. The gular fold is strongly developed and extends across the shoulders. 40–46 femoral and precloacal pores are arranged in a straight line along the thighs. Pores are present but smaller in females.

Adult male base color varies from gray-blue to brown, with pale blue flanks ( Figs. 1C , 4A ). The dorsolateral surface of the head is orange to yellow, extending past the shoulders. The extent of this coloration varies among individuals and depends on location but does not extend further than the mid-point of the axilla-groin length. A broad black lateral stripe begins posterior to the tympanum and terminates at the groin ( Figs. 1C , 4A ). The lateral stripe forms two separate blotches on the shoulder, one circular and enclosed entirely by orange to yellow coloration, while the other is elongated and wraps partly around the other. The remaining length of the lateral stripe is wavy edged or broken. On the ventral surface, males are cream with orange flushes on the belly, hindlimbs, and the length of the tail during the breeding season. A dark chest patch tapers to a point midbody and sometimes extends along the undersides of the forelimbs. This dark patch may vary in intensity, from black to gray. Male throat coloration in mainland populations is ultraviolet-blue with yellow to orange coloration along the gular fold ( Fig. 1A ); in Kangaroo Island populations, the base blue color is overlain with yellow reticulations ( McLean et al., 2014a; Fig. 1B ).

Adult females are cryptically colored, predominantly graybrown to orange-brown, densely patterned with darker and lighter speckling ( Fig. 4B ) and sometimes a thin, pale vertebral line. Similar to males, a black lateral stripe runs along the flanks, similar in shape to that of males but sometimes less prominent. White to cream on the ventral surface. Varying degrees of gray reticulations on the throat, sometimes with a blue tinge. Orange to yellow flushes on the belly and gular region during the breeding season. Juveniles resemble adult females in coloration and pattern. Color patterning remains visible in fresh spirit-preserved specimens but fades with time.

Measurements (mm) and meristic characters of lectotype.— (Bilateral meristics as left [L] and right [R]) SVL, 80; TL, 146.5; AGL, 37; HL, 25; HW, 19.5; HD, 11.5; EYE, 4.7; SL, 9.3; JL, 13.5; NW, 6.5; HUML, 14; RADL, 11.5; HANL, 14; FINL, 10.5; FEML, 17.6; TIBL, 21.3; FOOT, 30.1; TOE, 16.5; SUPRA, 15R/ 14L; INFRA, 18R/17L; ROSNAS, 5R/5L; SUPRANAS, 5R/5L; INTERNAS, 11; SDL, 30R/NA-L; FP, 24R/ 21L.

Distribution and natural history.— Ctenophorus decresii inhabits rocky areas and outcrops, sheltering in rock crevices. The species occurs in the Mount Lofty Ranges, on the Fleurieu Peninsula, and on Kangaroo Island in South Australia, Australia ( Figs. 2C , 3A , 6 ). These lizards occupy temperate habitats with varying levels of vegetation. Adults occur almost exclusively on rocks, perching conspicuously on elevated sites to bask and/or perform territorial and courtship displays. They are active in hot weather and, if disturbed, will run into a crevice or beneath a rock slab.

Figures

FIG. 1. (A) The blue mainland male throat of C. decresii sensu stricto and (B) the blue reticulated with yellow throat found on Kangaroo Island. The four male throat morphs of Ctenophorus modestus: (D) orange, (E) yellow, (F) orange-yellow (yellow with an orange central patch), and (G) gray. Male dorsolateral patterning and coloration differ where (C) C. decresii sensu stricto has a more ‘‘pinched’’ or broken lateral stripe with a greater extent of bordering orange or yellow coloration, and (H) C. modestus has a relatively straight edged lateral stripe with cream and orange coloration terminating at the shoulder.

FIG. 4. Males (A, C) and females (B, D) of Ctenophorus decresii (A, B) from Palmer and Mengler’s Hill Lookout, respectively, and C. modestus (C, D) from Telowie Gorge, all from South Australia, Australia (photos: copyright Adam Elliott).

FIG. 5. (A) Dorsal (left) and ventral (right) photographs of the lectotype of Ctenophorus decresii (Duméril and Bibron, 1837; MNHN 6545). This specimen is an adult male collected from Kangaroo Island, South Australia, in January 1803 (photos: Nicolas Vidal, Muséum national d’Histoire naturelle Paris). (B) Dorsal (left) and ventral (right) photographs of the lectotype of Ctenophorus modestus (Ahl, 1926; ZMB 54516). This specimen is a subadult male from ‘‘Australien’’ without an exact locality or reference to a collector or donor (photos: Frank Tillack, Museum für Naturkunde Berlin).

FIG. 2. Genetic divergence between Ctenophorus modestus (northern Flinders Ranges [NFR], southern Flinders Ranges [SFR], Olary Ranges [OR]) and C. decresii (mainland south [MS] which encompasses the Mount Lofty Ranges and Fleurieu Peninsula, and Kangaroo Island [KI]) and specimens examined for morphological analyses. (A) Results of a Bayesian analysis of ancestry in the program STRUCTURE (K ¼ 2). Each vertical bar represents an individual and individuals are ordered by population and latitude (from north to south). The proportion of white and gray represents the proportion of C. modestus and C. decresii ancestry in each individual, respectively. (B) Two-dimensional principal coordinate plot (PCoA) showing pairwise genetic distances between individuals: Ctenophorus modestus (squares), C. decresii (circles). 95% confidence ellipses of each population are shown. Both A and B were constructed from a genomic SNP dataset of 1333 SNPs (n ¼ 148). (C) Map showing geographic locations of samples of C. modestus and C. decresii shown in A and B.

FIG. 3. (A) Map showing localities of examined museum specimens: Ctenophorus modestus (squares); C. decresii sensu stricto (circles); C. fionni (triangles); and C. vadnappa (plus [þ]). Specimens without GPS coordinates are excluded. (B–C) Linear discriminant analyses of (A) males and (B) females based on 23 variables: Ctenophorus modestus (squares); C. decresii (circles); C. fionni (triangles); and C. vadnappa (plus [þ]). 95% confidence ellipses are shown. The lectotypes (males) and paralectotypes (females) of C. modestus and C. decresii are indicated with arrows.

FIG. 6. Geographic distribution of Ctenophorus modestus (squares) and C. decresii (circles) based on specimens in Australian Museums from the Atlas of Living Australia (data: https://doi.org/10.26197/ 5d91626857226); coordinates which were likely inaccurate (e.g., unsuitable habitat) were removed. Protected areas described in the Collaborative Australian Protected Areas Database (CAPAD, 2018) are shown as gray areas. The extent of occurrence is shown for C. modestus (49,102 km2; orange lines) and C. decresii (6,604 km2 total [mainland: 5,772 km2; Kangaroo Island: 832 km2], blue lines).