Craugastor gabbi, Arias, Erick, Chaves, Gerardo, Crawford, Andrew J. & Parra-Olea, Gabriela, 2016

Arias, Erick, Chaves, Gerardo, Crawford, Andrew J. & Parra-Olea, Gabriela, 2016, A new species of the Craugastor podiciferus species group (Anura: Craugastoridae) from the premontane forest of southwestern Costa Rica, Zootaxa 4132 (3), pp. 347-363 : 354-358

Craugastor gabbi sp. nov.

Gabb's Dirt Frog

( Figures 4–6 )

Craugastor stejnegerianus (part): Scott 1976; Savage 2002; Crawford 2003; Santos-Barrera et al. 2008 Holotype. UCR 21864, an adult female from the Organization for Tropical Studies’ Las Cruces Biological Station (+8.7889º, -82.9583º; 1200 m elevation), Fila Costeña, San Vito de Coto Brus, Puntarenas Province, Costa Rica; collected by Erick Arias, Gerardo Chaves, Adrián García-Rodríguez, and Federico Bolaños on 16 March 2013.

Paratypes. Adult male UCR 21865 and UCR 21867; adult female UCR 21863 and UCR 21876; same data as the holotype.

Assignment to group. The following inclusion characteristics were used to assign frogs to the C. podiciferus species group: narrow head (31–38% SVL), presence of venter areolate, a shorter Finger I than Finger II, absence of inner tarsal fold, and absence of nuptial pads.

Diagnosis. A small species of the Craugastor (Craugastor) podiciferus species group with the following characteristics: (1) skin on the dorsum is shagreen with scattered enlarged granules; venter and flanks are coarsely areolate, usually with dorsolateral and lateral folds; discoidal fold complete laterally and posteriorly; (2) tympanum round, usually with membrane differentiated and annulus prominent, (TY/ED = 39–111%), usually without supratympanic fold; (3) snout subovoid in dorsal view, rounded in profile; loreal region concave; canthus-rostralis usually rounded; (4) upper eyelid granular (EW/IOD = 50–103%); cranial crests absent; (5) vomerine teeth transverse, in two fascicles well behind the choanae; choanae smaller than the dentigerous; (6) vocal slits absent; nuptial pads absent; (7) Finger I slightly shorter than Finger II; disks usually absent, but with terminal transverse grooves; tips usually lanceolate; pads triangular; (8) fingers lacking lateral fringes; thenar and palmar tubercles ovoid, thenar much smaller than palmar; proximal supernumerary tubercles rounded; usually two accessory palmar tubercles; subarticular tubercles round, projecting and obtuse; (9) ulnar fold absent, but tubercles sometimes are visible; (10) heel lacking tubercles; inner tarsal folds usually absent; (11) inner metatarsal tubercle elongate, outer rounded, much smaller than inner; proximal supernumerary tubercles rounded; numerous (usually 10–15) rounded plantar tubercles; subarticular tubercles ovoid, projecting and obtuse; (12) Toe III larger than Toe V; disks expanded, asymmetric; disk cover usually lanceolate; disk pad triangular; toe webbing basal, usually does not reach the proximal subarticular tubercle on Toes I-II-III-IV; however, in some specimens webbing reaches the proximal subarticular tubercle or beyond; (13) dorsum gray brown to dark brown, uniform, mottled, some specimens have a middorsal light stripe, or, rarely, paired dorsolateral light stripes; venter cream with dark pigment reaching the midline; throat usually yellowish with dark mottling; upper surfaces of thighs usually with dark bars; posterior surface of thigh uniform reddish brown; usually labial bars and supratympanic mark ( Fig. 4 ); (14) SVL in males 14.35–21.35 mm; SVL in females 13.60–21.55 mm.

Comparisons with other species. Craugastor gabbi differs from all the other craugastorids of Lower Central America, except for those in the C. podiciferus species group, which have basal webbing between the toes and a narrow head, i.e., head width 31–38% SVL. Craugastor gabbi differs from other members of the C. podiciferus species group by having the following characteristics (condition for C. gabbi in parentheses, see Table 4 ). Craugastor gabbi differs from C. bransfordii , C. polyptychus and C. underwoodi by having a thenar tubercle equal to or slightly smaller than the palmar tubercle (thenar tubercle definitely much smaller than palmar tubercle, Fig. 5 ); C. gabbi differs from C. podiciferus by having a prominent calcar tubercle on the heel (calcar tubercle absent) and by the absence of supernumerary tubercles (supernumerary tubercles well defined in fingers and toes); from C. jota ( Lynch 1980) by having a prominent calcar tubercle on the heel (calcar tubercle absent); from C. lauraster by having an immaculate white venter (having a cream-colored venter with dark pigment reaching the midline, Fig. 4 ) and by having a much shorter Finger I than Finger II (Finger I slightly shorter than Finger II); from C. persimilis by having toes unwebbed (basal webbing between toes), by having dorsum and forelimbs areolate (dorsum and forelimbs shagreen), and by having a much shorter Finger I than Finger II (Finger I slightly shorter than Finger II); from C. stejnegerianus by having an immaculate white venter, [only the 8% of the specimens reviewed here had a venter with dark pigment reaching the midline] (venter cream-colored with dark pigment reaching the midline, Fig. 6 ) and by having a significantly larger TL/SVL and IOD/HW and a significantly smaller HL/SVL and E-N/SVL. Is important to note that the specimens of the northernmost populations of the Central Pacific of Costa Rica had the venter with dark pigment reaching the midline; however, these populations are under taxonomic revision because they could represent a separate species.

Description of holotype. Adult female; head width 36.5% of SVL; head length 38.6% of SVL; snout subovoid in dorsal view, rounded in profile; canthus-rostralis indistinct; loreal region slightly concave; nostrils small, directed laterally; vomerine teeth transverse, in two fascicles well behind the choanae; eye larger, diameter equal to 126.67% of E–N; tympanum small, 57.69% of ED, round, with membrane undifferentiated and annulus prominent; skin on dorsum shagreen, venter coarsely areolate, throat and head smooth, flanks shagreen like the dorsum; a pair of dorsolateral folds extend from the orbit to the sacrum, and a pair of lateral folds extend from the axillar level to the sacrum; discoidal fold complete; upper eyelid granular; postrictal tubercles fused forming a short ridge posterior-ventral to the tympanum.

Forelimb slim; ulnar tubercles and fold absent; thenar and palmar tubercles ovoid, with the thenar much smaller than palmar; proximal supernumerary tubercles rounded, medial supernumerary tubercles only on Finger III; three accessory palmar tubercles much smaller than the supernumerary tubercles; subarticular tubercles larger, round, projecting and obtuse; fingers slim; disks absent; fingers with grooves; tips of fingers lanceolate in dorsal view; pads triangular; fingers not webbed.

Hindlimb slightly slim; heel smooth, inner tarsal fold absent; inner metatarsal tubercle elongate, outer rounded, much smaller than inner; proximal supernumerary tubercles rounded, medial supernumerary tubercles only on Toes III and IV; numerous rounded plantar tubercles; subarticular tubercles rounded, projecting and pungent; disks expanded, asymmetric; disk cover lanceolate; disk pad triangular; webbing basal between Toes I-II-III-IV, reaching the proximal subarticular tubercle on Toe I.

Coloration of the holotype in ethanol ( Fig. 4 ). Dorsum of head and back dark brown to grayish with a pair of dark spots on each flank, a pair of dark spots on the back, an oblique dark stripe crossing the sacrum, and a middorsal light stripe; upper lip with diffuse dark bars; a dark supratympanic stripe extending from the orbit to the suprascapular shoulder; venter cream-colored and dotted with dark pigment; throat cream with dark mottling, not contrasting with the venter; groin cream, with a few small dark dots, not contrasting with the flanks; flanks light brown but transition dorsally to dark brown and ventrally to cream with dark dots, which penetrate the venter; dorsal surface of hind limbs similar to dorsal background with dark bars, which extend over the tibia and feet; posterior and anterior surfaces of hind limbs uniform dark brown.

Measurements of holotype (mm). SVL 19.7; HL 7.6; HW 7.2; ED 2.6; IOD 2.3; TY 1.5; EW 1.8; TL 10.4; E– N 2.1; T1 1.7; T2 3.7; T3 5.1; T4 9.50; T5 6.1; F1 2.4; F2 3.0; F3 4.2; F4 3.20.

Morphometric (mm) and morphological variation of paratypes. Morphometric variation of all specimens analyzed is summarized in Table 3. Here we provide the mean and standard deviation and, in parentheses, the range of each measurement of all the paratypes. SVL 16.9±2.0 (14.8–19.3); HL 6.7±0.81 (6.0–7.8); HW 6.2±0.8 (5.4–7.1); ED 2.3±0.3 (1.9–2.5); IOD 2.1±0.3 (1.8–2.5); TY in males 1.6, in females 1.4±0.2 (1.2–1.4); EW 1.3±0.3 (1.1–1.7); TL 9.3±0.9 (8.4–10.4); E-N 1.7±0.3 (1.5–2.1); T1 1.4±0.3 (1.1–1.7); T2 2.3±0.4 (2.7–3.6); T3 5.1±0.6 (4.5–5.9); T4 7.9±0.6 (7.2–8.4); T5 4.9±0.4 (4.6–5.4); F1 2.0±0.2 (1.8–2.3); F2 2.2±0.4 (1.8–2.6); F3 3.6±0.4 (3.0–4.1); F4 2.4±0.5 (1.9–3.0).

The scant variation among the paratypes is described as follows. Tympanic membrane differentiated in UCR 21863, UCR 21865, and UCR 21876; a pair of dorsolateral folds extending from the axillar level to the sacrum in UCR 21865 and UCR 21867; a pair of lateral folds extending from the orbit to the sacrum in UCR 21865; discoidal fold indistinguishable in UCR 21863, UCR 21865, UCR 21867 and UCR 21876; two tubercles postrictal in UCR 21867, semifused in UCR 21863 and UCR 21865; inner tarsal fold incomplete in UCR 21863. Fingers without medial supernumerary tubercles in UCR 21863 and UCR 21865; only two palmar accessory tubercles in UCR 21863, UCR 21865, and UCR 21876; toes without medial supernumerary tubercles in UCR 21863 and UCR 21865; dorsum with a pair of broad lateral light stripes extending from the snout to the groin, these stripes are divided by a pair of dark stripes extending from the axillar level to the groin, forming a stripe pattern in UCR 21876, with a pair of lateral light stripes extending from the orbit to the groin in UCR 21865; labial marks absent in UCR 21863; supratympanic mark absent in UCR 2 1876.

Variation in other specimens not observed in paratypes. Some specimens with the snout subelliptical in dorsal view; canthus-rostralis rounded in some; others with vomerine teeth obtuse; some specimens with a pair of dorsolateral folds extending from the orbit to the anus; lateral folds variable to absent, from the orbit to groin, from the orbit to anus, from the axillary level to sacrum and from the axillary level to groin; supratympanic fold distinctly curved downwards present in several specimens; some with only one postrictal tubercle; a specimen with inner tarsal fold complete; the inguinal gland was elevated and prominent in some individuals, in others this was not evident, although we did not observe a relation between this characteristic and sex. Some specimens with four or five ulnar tubercles in a row; some without grooves in fingers; at least one specimen with disk expanded in Fingers III and IV; webbing between Toes I-II can reach proximal subarticular tubercle, the web between Toes II- III-IV can reach least half of the proximal phalanx.

Patterns variation. In comparison with the other species of the C. podiciferus species group, C. gabbi had low levels of dorsal color pattern variation. The holotype had the formula MZ1OQ (mottled dorsal pattern with stripe supratympanic, skin texture irregularly granular and a pair of dorsal ridges); this formula was present in 25% of the specimens. The most common formula was UZ1OQ at 34.4%, described by Savage & Emerson (1970) as Morpho V. The following formulae were also observed: LZ1OQ present in 9.4%; UZ1NQ, MOQ, and MO present in 6.3%; UZ2OQ, LZ1NQ, LOQ, and MZ1NQ present in 3.1%.

The dorsal background color ranged from light gray to blackish brown; at least one individual presented longitudinal lines from the orbit to groin, light color on a dark background, and another two specimens presented dark lines on a light background. In eight individuals, the pattern of contrasting mottles was strongly prominent. The throat color varied from cream to dark brown, strongly contrasting with the lighter-colored venter. No association between the throat color and sex was observed. At least one individual had a well-defined mask, and the head of another was completely black. The supratympanic dark mark was present in most, but not all, individuals; labial bars were also present in most, but not all, specimens.

Natural history notes. Craugastor gabbi is abundant in the Fila Costeña, Coto Brus region. Santos-Barrera et al. (2008) reported this species at 21 of the 27 study sites, stating that C. gabbi was the most abundant amphibian in the forest and the coffee plantations and was also present in pastures. Usually, this species is associated with leaf litter. This species may reach densities of up 4586 individuals/ha ( Scott 1976). Craugastor gabbi is diurnal ( Savage 2002) and reproductively active throughout the year ( Santos-Barrera et al. 2008). The type series was found together in a patch of primary forest, active at approximately 12:00 h on the leaf litter and away from any body of water. No reproductive activity was observed, and no calls were recorded. The call is unknown, but it is likely an inconspicuous single slow squeak, as reported for C. stejnegerianus ( Savage 2002) . We did not find gravid females, and pairs in amplexus were not observed.

Geographic distribution. Craugastor gabbi is restricted to the premontane forest near the type locality of Fila Costeña, Costa Rica and the premontane forest of Cordillera de Talamanca in the extreme southwestern region of Costa Rica and western Panama near the present international border ( Fig. 1 ). The altitudinal range of the new species is 1100–1280 m elevation. Craugastor gabbi overlaps with the range of C. underwoodi and C. podiciferus at the Las Cruces Biological Station, Fila Costeña, Coto Brus.

Etymology. This species is named in honor of paleontologist William M. Gabb in recognition of his important contribution to the herpetology of Costa Rica as an explorer and collector, mainly in the Talamanca region.

Figures

FIGURE 1. Map showing the sampling sites. Samples indicated by the solid color were included in the molecular analyses, and the sites indicated by a number plus letters were included in the morphological analyses. Samples from the sites indicated by open circles and open triangles were included only in the morphological analyses. The numbers correspond to the locality ID in Table 1. Letter codes refer to Table 2.

FIGURE 5. Comparison of the thenar and palmar tubercles. a) Craugastor gabbi sp. nov. holotype (UCR 21864) showing smaller size of thenar tubercle compared to the palmar tubercle and b) C. bransfordii (CRARC 0177) of Turrialba, Costa Rica showing thenar tubercle to be equal to or slightly smaller than the palmar tubercle. This condition is also seen in C. underwoodi and C. polyptychus. Photo A by E. A and B by Brian Kubicki.

FIGURE 6. Ventral coloration. a) Craugastor gabbi sp. nov. paratype (UCR 21876), with the dark pigment reaching the midline and b) C. stejnegerianus (UCR 20885) of Palmar Norte, Costa Rica showing immaculate venter. Photos by Mauricio Calderón-Rivera.

FIGURE 4. a) Dorsal and b) ventral photos of Craugastor gabbi sp. nov. holotype (UCR 21864). The scale bar represents 0.5 cm. Photos by Mauricio Calderón-Rivera.