Ptenopus circumsyrticus, Becker & Alexander & Tolley, 2025

Becker, François S., Alexander, Graham J. & Tolley, Krystal A., 2025, Singing on key: An integrative taxonomic revision of barking geckos (Gekkonidae: Ptenopus) with six additional species and keys for morphology and advertisement calls, Vertebrate Zoology 75, pp. 277-323 : 277-323

Ptenopus circumsyrticus sp. nov.

Figures 13 , 14 , 20 E

Common names.

Interdune barking gecko

Afrikaans: Duinstraat blafgeitjie

Chresonymy.

Ptenopus garrulus (in part) – Brain (1962: fig. 3; central Namib)

Ptenopus garrulus maculatus (in part) – Haacke (1969: fig. 3 b – c), Haacke (1975: 225; central Namib Desert, notably Gobabeb)

Comment.

Specimens of P. circumsyrticus sp. nov. were not included in the earliest mentions of the name P. g. maculatus (e. g., FitzSimons 1935), but were included in several later works, including notably those of Haacke (1964, 1969, 1975). Haacke (1969) described the calls of both P. maculatus sensu stricto and P. circumsyrticus sp. nov. from the area surrounding Gobabeb, under the name ‘ P. g. maculatus ’, noting the clear differences. However, Haacke did not manage to match the two distinct calls with particular specimens in the area where they are sympatric (on the gravel plains of the central Namib Desert), and hence was uncertain about whether the different calls reflected intraspecific or interspecific variation. It is also worth noting that, in this sympatric zone, the two species can be readily distinguished by the internasal scale in P. circumsyrticus sp. nov. being large and in broad contact with the rostral, separating the nasal scales clearly, whereas P. maculatus has one or more small and rounded granules, barely separating the nasal scales. This morphological distinction is less clear in allopatric populations.

Holotype.

NMNW R 11394 , adult male, collected from the interdunes plains south of the Kuiseb River from Gobabeb Research Station , || Karas Region, Namibia ( –23.57053, 15.03618, 415 m a. s. l.), by Francois S. Becker on 6 September 2022.

Paratypes.

NMNW R 11395 ( allotype, adult female), R 11396 and R 11622 ( adult males), with the same collection details as the holotype ; R 11346 ( adult male) and R 11371 ( adult female), collected near the type locality ( –23.5697, 15.0388), by Francois S. Becker on 17 September 2021 .

Additional material examined.

See Table S 1 for vouchered (3) and unvouchered photographed specimens (13), DNA samples (16 available, 11 sequenced), and call recordings (11) included (total n = 25 excluding types).

Etymology.

This species is named in reference to its habitat: It occurs in and around the sand sea, on interdune plains or dune streets, and on sandy plains at the edge of the sand sea. They do not occur on the dunes themselves. Thus, we use the specific epithet “ circumsyrticus ”, the Latin adjective meaning “ around the dune ”, framed in the male genitive to match the gender of Ptenopus .

Diagnosis.

A moderately small Ptenopus ( SVL max. 54.9 mm, mean 48.6 mm, n = 16) with a short tail ( TL 62 % [range 48–73] of SVL, n = 8) and a lean appearance. It is distinguished from P. kochi , P. carpi , and P. sceletus sp. nov. by being substantially smaller; toes being intermediately fringed laterally (vs. weakly fringed in P. carpi and P. sceletus sp. nov. and extensively fringed in P. kochi ), with fringe length being at least half the breadth of the toe between fringes (vs. generally less than half in P. carpi and P. sceletus sp. nov., generally equal to in P. kochi ), although fringing can be more extensive in specimens found in looser sand, such as close to Walvis Bay or Far East Dunes; by dorsal colour pattern, characterised by paired, large, subsymmetrical, light ovoid markings interspaced by dark blotches (vs. spotted pattern in P. kochi and banded pattern in P. carpi and P. sceletus sp. nov.). It is further distinct from P. carpi and P. sceletus sp. nov. by the nasals being more swollen and the nostrils partially covered by internal projections of the upper labials; from P. kochi by having fingers laterally fringed with pointed triangular scales (vs. elongated pointed scales in P. kochi ), having white pigmented scales on entire ventral surface (vs. pink, unpigmented patches on the tail and limbs in P. kochi ), and having MBSR 108–179 (vs.> 180 in P. kochi ), with finer lepidosis presenting in specimens found in looser sand.

From congeners previously included in ‘ P. garrulus ’ it is distinguished by: The internasal scale usually being larger and broader than other species, with IN / INSBB being generally lower (median 4.5, range 3.6–5.8, but usually <4.7) than other species (usually> 5.0); having higher RB / RH (median 1.27, usually> 1.17) than P. adamanteus sp. nov., P. australis sp. nov., and P. garrulus (usually <1.17); having higher INS / NB (~ 1.61, usually> 1.10) than P. adamanteus sp. nov., P. australis sp. nov., and P. garrulus (usually <1.20); having lower MBSR (median 144, usually <160) than P. kenkenses sp. nov. and P. garrulus (usually> 160); higher IOS / MBSR (median 0.31, usually> 0.25) than P. maculatus and P. garrulus (usually ≤ 0.25); having only one inernasal scale in contact with the rostral, while P. australis sp. nov. has three; having no pink, inpigmented scales on the soles (vs. some unpigmented scales in P. garrulus and P. australis sp. nov.).

Holotype description.

(Fig. 13 ). Adult male, SVL 48.75 mm with original tail 35.79 mm (73.42 % SVL). Body and head covered with minute hexagonal to round scales of a similar size, dorsally and ventrally, with scales on limbs notably larger. Small mid-ventral incision for removal of liver sample. Body and head slender, MBSR 129, IOS 53, HL 14.62 mm, HW 10.99 mm, HH 5.57 mm, EED 5.81 mm. Upper and lower labials 8, six granules bordering the mental. Clear but not prominent superciliary ridges tapering above mid-eye level; a single row of elongated scales around the anterior and upper margins of the eye with curved tips posteriorly, the scales being smaller and rounder along the posterior and dorsal edges; nasal scales swollen, the prenasals separated by one large, hexagonal internasal scale in broad contact with the rostral, with IN / INSBB 4.69, INSH / NB 1.09; nostrils partially covered by projection from the upper nasal. Rostral broad, with RB / RH 1.44, MB / RB 0.81. Eyes intermediate, EYE 3.15 mm, pupil vertical. Ear opening is oblique (~ 45 °) and narrow, with small, slightly projecting scales at the anterior margin. Toes elongate, flattened, with elongate fringed scales, small, pointed, triangular fringes on the fingers; strong nails on fingers and toes, being larger and thicker on the fingers.

Colouration.

In life, the holotype (Fig. 14 A ) has a dorsal background colour of ochre with deep orange, cream, and dark brown spots, the darker spots aggregated in clusters; three pairs of larger, cream / light yellow, ovoid markings from the neck to the back, with one unpaired marking on the left lower back and another asymmetrical pair onto the tail base; light markings interspaced by diffuse, asymmetrical, mottled or spotted, dark brown patches; the tail has 11 dark bands, unevenly spaced and somewhat diffuse, with the last being very faint; the dorsal colours and markings fade to grey on the lateral edges with clear alternating light-and-dark markings; immaculate white ventrum. Yellow gular patch with faded edges.

In preservative (Fig. 13 ), the lighter colours have faded to off-white or beige, and all the darker colours appear various shades of dark brown or grey with some orange being evident. The yellow has faded completely.

Variation.

Refer to Table S 1 and Figure 4 for range of morphometric characters, including the paratypes. Internasal scale typically large and symmetrical; rostral typically broad; toe fringes relatively extensive, notably more so in areas with looser sand. As with other species, the colour of the animals usually matches that of the local substrate, although the patterning is similar to the holotype (Fig. 14 ). Background colour variations include ochre to brick red. Ventrally animals are immaculate white. Males have faded to bright yellow gular patches (typically less extensive than most other species), occasionally with slight yellow on hidden dorsal surfaces of the hind leg.

Advertisement call.

The advertisement call (Figs 3 , 20 D ) consists of 4.6 notes (range 3–7), uttered slowly at a rate of 2.44s - 1 (range 1.57–3.68). Note duration is long (48 ms [range 31–57]) and regular (note 1 duration deviance 16 % [range 3–28]), with long, highly regular intervals (inter-note interval range 13 % [range 10–20]) inter-note intervals of 385 ms (range 237–587). Median call density is low (0.129 [range 0.09–0.17]) and call duration is 1.49s (range 1.1–2). The basal frequency is ~ 383 Hz (range 308–474), but very soft and may be inestimable, with harmonic bands louder towards the (upper) dominant frequency at 3.8 kHz (range 3.5–4.1); no clear lower peak frequency is evident. Frequency appears to modulate up by ~ 0.5 kHz in the course of the note, but (human) perceived pitch is usually monotonous throughout the notes and call. Bandwidth (90 %) is difficult to estimate consistently: approximately 1–4.7 kHz.

The call strongly resembles the sound of bouncing marbles and on a warm evening on the interdunes thousands can be heard calling in chorus. Call period (mean 133 s) varies greatly, but can be as brief as 16 seconds during peak chorus activity. This species tends to occur (and call) at higher densities than the sympatric congeners P. maculatus and P. kochi . It calls from shortly before sunset and calling activity may continue throughout the night as long as the moon is above the horizon, particularly on warm evenings. This species occasionally calls during the day, especially during foggy or cloudy conditions, but generally not during rainy conditions.

Habitat and distribution.

This species occurs on sandy soils including interdune plains within, and sandy plains around the northern and eastern edges of the Namib erg, Namibia (Fig. 5 ). It generally does not occur on the gravel plains north of the Kuiseb River except in a few sandier patches east of 15 ° longitude. This population is genetically divergent from other nearby populations in the Namib erg. It does not appear to occur along the south-eastern corner of the Namib erg, where slightly harder Arenosols are occupied by P. kenkenses sp. nov., or along the southern or south-western edges of this erg, where the same soils are occupied by P. adamanteus sp. nov.

It has not been found in sympatry with P. kenkenses sp. nov., but overlap is likely in the southern portion of its range. It occurs parapatrically alongside P. kochi , P. maculatus , and possibly P. carpi sensu stricto (near the northern border of the Kuiseb River), as these species occupy different substrates in close geographic proximity. Occasionally, it has been found in sympatry and even syntopy with P. maculatus on the sandier patches of the gravel plains north of the Kuiseb River, and with P. kochi in the Namib erg, near the edges of the interdunes where the two species’ preferred substrates overlap. On broad interdunes, P. circumsyrticus sp. nov. occurs in allopatry.

Natural history.

The peak calling and breeding season is in the austral spring to summer (August to November), although some calling may take place outside this period. Two eggs (dried out) have been recovered from an abandoned burrow, so clutch size can be up to two. The burrows are generally less complex than the parapatric P. kochi and P. maculatus , and appear to be inhabited solitarily. Very small juveniles have been observed in burrows of their own. While multiple natural predators for Ptenopus spp. have been observed and hypothesised ( Haacke 1975), one observation of a P. circumsyrticus sp. nov. being carried off by a large solifuge (le Roux pers. com. 2022) certainly constitutes a novel observation.

Figures

Figure 3. Box and whisker plots of the bioacoustic characters analysed using ANOVA / Kruskal-Wallis tests, for species of Ptenopus. Numbered characters (numbered as in Methods) and their units are indicated on y-axis labels. Species colours correspond to those on Figure 2 and indicated on the key. Significant differences (according to pairwise post hoc tests) are indicated through homogenous groupings: Species not significantly different in the present character are one group, as indicated by lower-case letters. Species that share the same letters not differing significantly from each other; species with multiple letters are not significantly different from any other species sharing those letters. Approximate divisions between the groups are indicated by dotted lines perpendicular to the y-axis, and the group letters are indicated to the right of each graph.

Figure 4. Box and whisker plots of the morphological characters analysed using ANOVAs or Kruskal-Wallis tests, for cryptic species of the Ptenopus garrulus group. Numbered characters (numbered as in Methods) are indicated on y-axis labels: 1. Internarial / internasal scale base breadth; 2. rostral breadth / height; 3. internasal scale height / nostril breadth; 4. mid-body scale rows; 5. interorbital scales; 6. interorbital / mind-mody scales; 7. inter-nasal scales. Species colours correspond to those on Figure 2 and indicated on the key. Significant differences (according to pairwise post hoc tests) are indicated through homogenous groupings: Species not significantly different in the present character are one group, as indicated by lower-case letters. Species that share the same letters not differing significantly from each other; species with multiple letters are not significantly different from any other species sharing those letters. Approximate divisions between the groups are indicated by dotted lines perpendicular to the y-axis, and the group letters are indicated to the right of each graph.

Figure 5. Revised, interpreted distributions of Ptenopus species in southern Africa (high resolution map, can be zoomed for detail). Some species’ ranges overlap, shown with translucent overlapping shapes on the map. Others likely occur parapatrically along extended contact zones, represented by opaque, touching shapes. For further clarity, co-occurrence patterns for all species pairs are shown on Table 5, and confirmed individual records on Figure 2.

Figure 13. Holotype (NMNW R 11394) of Ptenopus circumsyrticus sp. nov. from Gobabeb, Erongo Region, Namibia (– 23.5705, 15.0362). Scale bar = 1 cm relative to full ventral and dorsal views. Photos by Francois S. Becker.

Figure 14. Life colour variation in Ptenopus circumsyrticus sp. nov.: A NMNW R 11394 (holotype) from Gobabeb, Erongo Region, Namibia (– 23.5732, 15.0368); B FB 2003 (unvouchered) from Keerwerder, NamibRand, Hardap Region, Namibia (– 24.9818, 15.9338); C, D FB 2080 from NE of Gobabeb (– 23.3175, 15.5700); E unvouchered specimen from near locality of C; F NMNW R 11355 (paratype) from near locality of B (– 24.9495, 16.0397). Photos by Francois S. Becker.

Figure 20. Sonograms (top graphs) and oscillograms (bottom graphs) of representative advertisement calls of Ptenopus species (A – J, species names indicated on graphs). Both x and y axes are directly comparable / equally scaled across species. Specimen numbers and localities: A NMNW R 11585, NE of Koës, Hardap Region, Namibia; B iNaturalist 140169978 (Jacobus Retief), Merweville, Western Cape Province, South Africa; C NMNW R 11622, E of Lüderitz, || Karas Region, Namibia; D NMNW R 11643, SW of Gobabeb, Erongo Region, Namibia; E NMNW R 11657, NE of Keetmanshoop, || Karas Region, Namibia; F NMNW R 11704, Gobabeb; G NMNW R 11716, Hoanib River, Kunene Region, Namibia; H NMNW R 12114, Gobabeb; I NMNW R 11843, NW of Gobabeb; J NMNW R 11790, N of Swakopmund, Erongo Region, Namibia. The audio files on which this figure is based, are made available (File S 2).