Ptenopus carpi Brain, 1962

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 carpi Brain, 1962 sensu stricto

Figures 17 , 20 J

Common names.

Carp’s barking gecko

Afrikaans: Carp se blafgeitjie

Chresonymy.

Ptenopus carpi Brain, 1962 : plates 1 b, c, e, fig. Ib, Haacke (1964: 3), Mertens (1971: 44), Haacke (1975: 230; in part)

Comment.

The type locality of P. carpi is “ gravel plain approximately 1 mile north of the Kuisib R. [Kuiseb River] at Gobabeb, Central Namib Desert [Erongo Region], S. W. A. [ Namibia] ” (-23.5456, 15.0400). Currently, no P. carpi can be found at this location. The closest location of current occurrence from Gobabeb, is 9 km to the northwest. Charles Brain’s son, Conrad Brain, who had attended the field trip, claims that they were a little lost that evening and likely the real type locality was more to the northwest, where the species currently occurs (Brain pers. comm. 2023).

Here, we split “ P. carpi ” into two species. The topotypical population south of the Swakop River is assigned the name P. carpi sensu stricto, while P. sceletus sp. nov. is described from north of the Swakop River, below. We hereby restrict the range of P. carpi sensu stricto to between the Kuiseb and Swakop rivers. In light of this revision, the advertisement call of P. carpi sensu stricto has not been recorded or described before; Gramentz (2008) briefly described the call of P. sceletus sp. nov. (based on a single specimen collected north of the Swakop River) under the name “ P. carpi ”.

Ptenopus carpi sensu stricto is the only member of this genus that lacks sexual dichromatism, with both sexes displaying a yellow gular patch (Fig. 20 E ). The observations of FB contradict the original description of P. carpi ( Brain 1962) in which females, collected in the month of May, apparently had no gular patch. Haacke (1975), who collected P. carpi extensively from around the type locality, made observations corresponding with our own: That all P. carpi females possess a yellow gular patch. Haacke surmised that the presence of these patches on females may be seasonal. However, we have collected, photographed and observed multiple P. carpi sensu stricto females from across their range including the type locality and throughout the year (see Table S 1; many additional observed individuals not tabled) and have not observed any female P. carpi sensu stricto without a gular patch; nor have we observed a gular patch in any P. sceletus sp. nov. females. Since the gular patches fade shortly after specimen preservation (not mentioned by previous authors), we argue that Brain (1962) may have assumed that sexual dichromatism was present while describing the species based on the preserved specimens, and failed to notice the gular patches on the live females. Alternatively, the gular patch may be missing under rare circumstances, although under what circumstances we shall not surmise.

Holotype.

TM 25973 , adult male, collected “ on gravel plain approximately 1 mile north of the Kuisib R. [Kuiseb River] at Gobabeb , Central Namib Desert [in the Erongo Region], S. W. A. [ Namibia] ” (probably –23.5456, 15.0400), by Charles K. Brain in May 1959.

Paratypes.

TM 25966 –70, 25972, 25974–25979, 25981–86, 25990–93, 25995, 25997–8, 26207 (10 adults, 10 subadults and 6 juveniles), all from the same locality as the holotype .

Material examined.

See Table S 1 for unvouchered photographed specimens (49), DNA samples (32 available, 9 sequenced), and call recordings (3) included (n = 51).

Diagnosis.

A large Ptenopus (SVL max. 64.7 mm, mean 53.7 mm, n = 33) with a moderate tail (TL 66.7 % [range 61–72] of SVL) and lean appearance, with slender limbs and reduced toe fringes compared to other species. Preserved specimens are morphologically indistinguishable from P. sceletus sp. nov., but usually have a longer snout or narrower head (than P. sceletus sp. nov.), clearly visible from below (compare Figs 17 E and 19 E ); live specimens can be distinguished by lack of sexual dichromatism, with females having a yellow gular patch as in males (Fig. 17 E , vs. no female gular patch or very faint yellow in P. sceletus sp. nov.), and by red or ochre iris colouration (Fig. 17 F , vs. silver to brown in P. sceletus sp. nov.). This species and P. sceletus sp. nov. are the only members of the genus with a clearly banded dorsal colour pattern on the body and tail. For a more detailed morphological diagnosis and description, see Haacke (1975).

Advertisement call.

The advertisement call (Figs 3 , 20 I ) consists of 10 (9–12) notes uttered in slow succession, with a note rate of 2.25s - 1 (range 1.68–3.01). Note duration is short (26 ms [range 22–29]) and regular with note 1 duration deviance 12.8 % (range 5.5–24.8). The inter-note intervals are the longest of any species (560 ms [range 323–682]) and usually irregular, the inter-note interval range being the highest of any species (84 % [range 62–105]); intervals are longer at the start and sometimes end of the call, but notably shorter in the middle: The call starts slow, speeds up, and then sometimes slows again. Median call density is the lowest of all species (0.06 [range 0.05–0.08]) and call duration is very long (3.6s [range 3.3–3.8]). The basal frequency is 392 Hz (range 310–517) but very soft and usually inestimable, with harmonic bands louder towards the dominant frequencies, with the upper dominant frequency at 3.5 kHz (3.3–3.8) and a clear lower dominant frequency (sometimes more emphasised than the upper) around 1.4 kHz (1.1–1.9), less than half the upper dominant or frequency. Frequency appears to remain constant throughout the notes and call, as with the (human) perceived pitch, which is low and monotonous compared to most other species. The call is also notably softer than most other species. Bandwidth (90 %) is difficult to estimate consistently, but is broad: approximately 2–5 kHz.

The call seems to vary more than other species, with calls sometimes having as few as one to three notes, especially late at night. Call period (mean 349 s) varies greatly, but is usually much lower than other species, and has not been recorded any faster than 2 min during peak chorus activity. This species does not chorus as notably as other species.

Calling activity is crepuscular to nocturnal, calls starting well after sunset and often continuing throughout the night to some degree. One instance of a notable chorus was recorded near Walvis Bay airport on 19 April 2018. Chorusing started abruptly at ~ 25 min after sunset, and lasted for about 20 minutes, with very reduced calling activity continuing later into the night. Calling appears to be somewhat seasonal with a peak around April to August, coinciding with lower fog incidence. Calling activity is more pronounced on warmer evenings but may continue despite cold, foggy conditions.

As with other species, P. carpi calls from the burrow entrance, although it may also call (advertisement call) occasionally while roaming. This could not be observed directly, but a wandering gecko was often spotted in the area where a call was just heard. Having said that, wandering geckos are easier to spot than geckos in a burrow.

Distribution and habitat.

Ptenopus carpi occurs on hard gravel plains in the central Namib Desert, Namibia, from the northern banks of the Kuiseb River to the southern banks of the Swakop River, central Namib Desert (Fig. 5 ). It does not tolerate soft, sandy substrates. Ptenopus carpi occurs in the Atlantic fog band, from the high water mark to approximately 50 km inland. It is one the most common vertebrates on these coastal desert plains, but becomes increasingly rare to the east of its range. Here, it occurs syntopically with P. maculatus , and parapatrically with P. kochi and P. circumsyrticus sp. nov. along the Kuiseb River (the latter species occurring in or south of the river, while P. carpi occurs north of it). Ptenopus carpi and P. kochi can occasionally be found only metres from each other, on two different substrates. Ptenopus carpi occurs parapatrically with P. sceletus sp. nov. across much of the Swakop River, and sympatrically in the Rössmund area just south of the river.

In light of this revision, P. carpi has a restricted range, estimated at ~ 1400 km 2. While most of its range is presently encapsulated by statutory protected areas (Namib-Naukluft National Park and Dorob Park), on the ground management of the habitat in these areas is poor. In particular, mining and industrial activities and the degradation of the gravel plains by motorists occurs within this the protected areas. The result is that more than 80 % of the species range is currently within zones encompassing active mining licenses, exclusive prospecting licenses, and reconnaissance licenses ( Spatial Dimension 2024), and / or occupied by urban and industrial developments, an airport, and a military base. Considering the extensive geographic scope of these claims and properties, there are likely between four and ten threat locations according to IUCN guidelines (IUCN 2022). Given the continued decline in the extent and quality of its habitat, and the range of threats noted here, a full IUCN assessment could result in the species qualifying for a range of threat categories falling between NT and EN (B 1 ab).

Natural history.

The breeding season for P. carpi appears to be between April (earliest recorded calls) and August, with some juveniles having been found between November and February.

Ptenopus carpi does not call nearly as often as congeners (similar to P. sceletus sp. nov.) but appears to spend more time wandering on the surface, even far from its burrow. It is active much later into the night than congeners, often only emerging well after dark, and its activity is not dampened by cold or foggy conditions (as in most other species, except P. sceletus sp. nov. and, occasionally, P. adamanteus sp. nov.).

The burrow is usually shallower and simpler than those of other species but may have two to three side-branches and typically has an escape exit (as in other species). Gravid females observed (FB) generally contain two eggs, which are presumably laid in the burrow, as in other species.

Ptenopus carpi utters two different calls: The advertisement call and the single-pulse call, also previously noticed for the closely related P. sceletus sp. nov. ( Gramentz 2008). Gramentz (2008), based on observations in captivity, suggested the single-pulse call may be a threat call, but FB’s observations suggest this is not the function. This call is not notably uttered in response to disturbance or the close presence of a threat, and the first individuals to utter this call were often far from the observer. This call is uttered frequently in the wild by both P. carpi and P. sceletus sp. nov., usually late at night after chorusing has ceased. Individuals clearly respond to each other, with several answering the first call uttered within a second or two. It is possible that this is a spacing mechanism, or a way for individuals to keep track of the population’s general location as they wander on the surface. A squeak may be uttered if the animal is molested (as with other species) but this is not similar to the single-pulse, which is identical to a single note in the advertisement call. For more details on the natural history of P. carpi , see previous works ( Brain 1962; Haacke 1975).

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 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 17. Life colour variation in Ptenopus carpi: A NMNW R 11822 from Walvis Bay Airport, Erongo Region, Nambia (– 23.0003, 14.6695); B NMNW R 11809 from NW of Gobabeb, Erongo Region, Namibia (– 23.4530, 14.9637); C NMNW R 11815 from locality A; D NMNW R 11798 from locality A, NMNW R 11810, and NMNW R 11808 from NW of Gobabeb (– 23.4533, 14.9642), showing iris colouration variation from deep red to light ochre; E NMNW R 11808 (male) and NMNW R 11819 (female) from NW of Gobabeb (– 23.4235, 14.9353), showing clear gular patches on both sexes (patch size and shape varies in both sexes, but tends to be more extensive in males). Photos by Francois S. Becker.

Figure 19. Life colour variation in Ptenopus sceletus sp. nov.: A NMNW R 12103 (paratype) from N of Swakopmund, Erongo Region, Namibia (– 22.6259, 14.5457); B NMNW R 12101 (allotype) from locality A; C NMNW R 11763 from Hoanib River, Kunene Region, Nambia (– 19.3539, 13.1453); D NMNW R 11754 from Henties Bay, Erongo Region, Namibia (– 22.1584, 14.3086); E NMNW R 12100 (holotype) and NMNW R 011771 from the same locality as A, showing sexual dichromatism in gular patches of this species (male gular patch may be divided or undivided, while female only has slight shades of yellow on lateral edges); F NMNW R 11771 from N of Swakop River near Swakopmund (– 22.6652, 14.57619) and NMNW R 11755 from N of the Omaruru River near Henties Bay (– 21.7703, 14.5520), showing iris colour variation from silver (most common in the sourthern extreme of the range) to brown (more common further north). 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).