Guibemantis vakoa, Gabriel & Rothe & Köhler & Rakotomanga & Edmonds & Galán & Glaw & Lehtinen & Rakotoarison & Vences, 2024

Gabriel, Hugh, Rothe, Laila-Denise, Köhler, Jörn, Rakotomanga, Sandratra, Edmonds, Devin, Galán, Pedro, Glaw, Frank, Lehtinen, Richard M., Rakotoarison, Andolalao & Vences, Miguel, 2024, Unexpected diversity and co-occurrence of phytotelmic frogs (Guibemantis) around Andasibe, one of the most intensively surveyed amphibian hotspots of Madagascar, and descriptions of three new species, Zootaxa 5397 (4), pp. 451-485 : 475-479

Guibemantis vakoa sp. nov.

( Figs 10 , 12)

Remark. Individuals of this species have been reported as Guibemantis sp. aff. bicalcaratus “Moramanga” by Glaw & Vences (2007), and as G. sp. 8 in Vieites et al. (2009) and G. sp. Ca 8 in Perl et al. (2014), but with incorrect field number information for the sample used therein (reported erroneously as ZCMV 466).

Holotype. ZSM 389/2004 ( ZCMV 931 ), adult male, collected by M. Vences, E. Edwards and C. Woodhead on 15 February 2004 at Besariaka (south of Moramanga), central eastern Madagascar, coordinates -19.12863, 48.28063, 976 m a.s.l.

Paratype. One specimen, ZSM 388/2004 ( ZCMV 930 ), adult male with same collection data as holotype .

Definition. Assigned to the subgenus Pandanusicola in the genus Guibemantis based on its small to medium body size, phytotelm-dwelling habitats (in Pandanus plants), near-absent webbing between toes, connected lateral metatarsalia, presence of both inner and outer metatarsal tubercles, intercalary elements between ultimate and penultimate phalanges of fingers and toes (verified by external examination), presence of well-delimited femoral macroglands consisting of discrete enlarged gland granules and without externally visible central depression and of whitish color laterally on throat (marking the vocal sac) in males (absence in females), and molecular phylogenetic affinities.

The new species is characterized by the combination of the following characters: (1) small size with adult SVL up to 24 mm in males (females unknown), (2) light brownish dorsal color, often without distinct darker markings or spots, (3) distinct brown rostral stripe, (4) a few, small whitish spots on (posterior) flanks, (5) absence of distinct dorsolateral stripes, (6) absence of webbing on hand and only traces of web on foot, (7) vomerine teeth present, (8) femoral (macro)glands of males distinct, very clearly recognizable and of contrasting orange-brown color in life, single gland granules well recognizable externally in life and preservative.

Although this combination of character states will allow a distinction from most other species of Guibemantis , it is more difficult to diagnose the species against other brownish-colored species, especially G. ambakoana , G. bicalcaratus , G. methueni , and G. wattersoni . The new species can be reliably diagnosed from all other Guibemantis species based on nucleotide positions in the mitochondrial 16S rRNA gene: MolD identified a robust diagnostic nucleotide combination of an 'G' in the site 998, 'A' in the site 1132, 'C' in the site 1251 (positions relative to the full 16S rRNA gene of Mantella madagascariensis ).

Diagnosis. Distinction from G. fotsitenda , G. liber , G. razandry , G. razoky and G. tasifotsy : male femoral gland consisting of a well-delimited field of discrete enlarged single gland granules (vs. a diffuse field of small granules covering most of the ventral shank), occurrence limited to Pandanus leaf axils (vs. calling and breeding in open swamps), and calls emitted from Pandanus vs. calls emitted from exposed perches above swamps.

Distinction from G. albolineatus : absence of well-delimited dorsolateral bands (vs. presence), and light brown ground color on dorsum (vs. chocolate-brown).

Distinction from G. albomaculatus : absence of fine white dotting on body (vs. presence, especially on hindlimbs and sometimes on dorsum), and males with white color only laterally on throat (vs. white color covering most of the throat).

Distinction from G. ambakoana : absence of light dorsolateral bands (vs. presence).

Distinction from G. annulatus : absence of a regular pattern of small dark dots dorsally (vs. presence), and absent or poorly contrasted light ring proximal to finger and toe discs (vs. distinct and contrasted).

Distinction from G. bicalcaratus : presence of a black vertical line in upper part of iris (vs. absence), and a weakly pigmented grayish flank with a few silvery white markings (vs. flanks of similar color as dorsum and without silvery markings).

Distinction from G. flavobrunneus : smaller body size (male SVL 23–24 mm vs. ≥ 30 mm), and dorsum more or less uniformly brown (vs. brown with contrasted light brown pattern).

Distinction from G. methueni : largely uniformly colored dorsum (vs. usually dark markings or spots on dorsum), femoral glands typically with contrasting yellow-orange color (vs. without contrasting color), and males with white color only laterally on throat (vs. white color covering most of throat).

Distinction from G. milingilingy : absence of dorsolateral bands (vs. broad and continuous dorsolateral bands), and dorsal color brown typically without greenish shade (vs. yellowish green dorsolateral bands and dorsal markings).

Distinction from G. pulcher and G. pulcherrimus : brown dorsal color (vs. translucent green), and absence of purple-reddish dots and markings on the dorsum (vs. presence).

Distinction from G. punctatus : absence of a regular pattern of small dark dots dorsally (vs. presence).

Distinction from G. rianasoa : larger body size (male SVL 23–24 mm vs. ≤ 20 mm), brown dorsal color (vs. olive greenish), and large femoral glands with contrasting yellowish color in males (vs. small and inconspicuously colored).

Distinction from G. wattersoni : absence of dorsolateral bands (vs. poorly contrasted bands usually present), and presence of a black vertical line in upper part of iris (vs. absence).

Distinction from G. woosteri : absence of dorsolateral bands (vs. poorly contrasted dorsolateral bands present), and a brown dorsal color without greenish elements (vs. often a green shade, especially of dorsolateral bands).

Description of the holotype. Adult male in good state of preservation ( Fig. 11 ). Tissue removed from ventral side of left thigh for DNA extraction. Head longer than wide and wider than body; snout pointed in dorsal and ventral views, more rounded in lateral view; canthus rostralis straight, loreal region flat; nostrils nearer to tip of snout than to eye, tympanum distinct, 43% of horizontal eye diameter; supratympanic fold distinct, curved; vomerine odontophores distinct, located medially between eye and choanae on either side of head; maxillary teeth present; tongue ovoid, and distinctly bifid at its tip. Arms slightly slender; relative finger length 1<2<4<3, second finger very slightly shorter than fourth finger; finger discs moderately enlarged and squared off at tips in a rounded ‘T’ shape, no webbing between fingers recognizable, subarticular tubercles distinct, unpaired. Hindlimbs moderately slender, foot length 91% of tibia length; lateral metatarsalia largely connected by muscular tissue; inner metatarsal tubercle oblong and recognizable, relatively small; outer metatarsal tubercle round, small and distinct; only traces of webbing recognizable between toes, relative length of toes 1<2<5<3<4, third toe slightly shorter than fifth; toe discs moderately enlarged. Femoral glands distinct and prominent. For morphometric measurements see Table 1 .

After almost 20 years in preservative ( Fig. 11 ), dorsal surface is beige with indistinct brownish spots and markings. The flanks are darker brown. No obvious light dorsolateral bands are recognizable. Forelimbs and hindlimbs beige-grayish, with brown crossbands. Ventral side beige. In life ( Fig. 9 ), dorsal surface was golden brown with a few dark brown spots, a dark brown rostral stripe was present, and limbs were grayish brown with dark brown spots and crossbands. A few silvery white spots were visible on the posterior flanks. Ventrally, mostly unpigmented/translucent, with very little white pigment on throat. Femoral glands were very distinct and contrasted, of orange-brown color.

Variation. The known males all have distinct brown-orange femoral glands and only a little amount of white color laterally on the throat ( Fig. 9 ). Females are unknown.

Etymology. The species name is derived from the Malagasy word “vakoa ”, used in eastern Madagascar to refer to Pandanus screw pines and used to highlight the occurrence of this species in Pandanus leaf axils. The name is used as a noun in apposition.

Natural history. Very poorly known. Specimens were found on 15 February 2004 in a forest fragment near Besariaka (destroyed by slash-and-burn agriculture two years later) in Pandanus plants, calling during the day. At Besariaka, specimens occurred in syntopy with G. methueni .

Bioacoustics. Advertisement calls recorded on 15 February 2004 at Besariaka (air temperature 21°C; Fig. 4C ) consist of a single very short click-note, emitted at long, somewhat irregular intervals. Amplitude modulation is evident in each call, with maximum call energy present at the beginning of the call, gradually decreasing towards the call’s end. Numerical parameters of 28 analysed calls from at least two individuals are as follows: call duration (= note duration) 8–14 ms (10.2 ± 1.7 ms); inter-call intervals 623–1286 ms (869.5 ± 214.3 ms); dominant frequency 3521–3972 Hz (3720 ± 206 Hz); prevalent bandwidth 2000–5500 Hz. Call repetition rate was approximately between 65–85 calls/minute.

Calls recorded in 2007 at Betampona ( Rosa et al. 2011, track 27, as G. sp. aff. bicalcaratus ) agree in character with those reported from Besariaka in consisting of a single very short click-note emitted at variable, but long intervals. Numerical parameters of 32 analysed calls are as follows: call duration (= note duration) 3–9 ms (5.9 ± 1.9 ms); inter-call intervals 471–1470 ms (767.9 ± 363.8 ms); dominant frequency 3423–3779 Hz (3576 ± 135 Hz); prevalent bandwidth 2000–5700 Hz.

Distribution. Besides (1) the type locality Besariaka, the species has also been recorded, based on genetic evidence, from (2) Sahafina, (3) Betampona, and (4) Fierenana ( Figs 1–2 ).

Figures

FIGURE 1. Maximum Likelihood tree based on a DNA sequences of a fragment of the mitochondrial 16S rRNA gene (alignment length 545 bp) for 368 specimens of all species and candidate species of Guibemantis. See Koppetsch et al. (2023) for a discussion of the mitochondrial non-monophyly of species in the G. liber complex (G. fotsitenda, G. liber, G. razandry, G. razoky).

FIGURE 2. Map of Madagascar showing genetically verified locality records of the target species of Guibemantis studied herein (colors as in Fig. 1). The base map shows vegetation across Madagascar from the Madagascar Vegetation Mapping Project (Moat & Smith 2007; formerly available at www.vegmad.org). Vegetation is colored as follows: green, humid forest (rainforest); red, western dry deciduous forest; bluish, western subhumid forest; orange, south western dry spiny forest-thicket; yellow, tapia forest.

FIGURE 4. Audiospectrograms and oscillograms of advertisement calls of six species of Guibemantis of the subgenus Pandanusicola. A, call series (containing 3 calls) of Guibemantis rianasoa sp. nov., recorded on 19 November 2022 at Andasibe. Recording high-pass filtered at 2000 Hz. B, two calls of Guibemantis ambakoana sp. nov., recorded on 19 November 2022 at Andasibe. Recording high-pass filtered at 1500 Hz. C, three calls of Guibemantis vakoa sp. nov. recorded on 15 February 2004 at Besariaka. Recording band-pass filtered at 1500–9200 Hz. D, call series (containing 5 calls) of Guibemantis methueni recorded on 8 November 2011 at Andasibe. Recording high-pass filtered at 1000 Hz. E–F, calls of G. annulatus (from Lehtinen et al. 2011) and G. pulcher (from Vences et al. 2011).

FIGURE 9. Male individuals of Guibemantis vakoa sp. nov. from Besariaka (south of Moramanga), photographed in 2004. (A–B) Holotype ZSM 389/2004 (ZCMV 931). (C–D) Paratype ZSM 388/2004 (ZCMV 930) (assigned to species based on morphology only). Note the distinct orangish-brown femoral glands and only limited white throat pigmentation in comparison to syntopic specimens of G. methueni which have less distinctly pigmented glands and extended white throat color (Fig. 10).

FIGURE 10. Male individuals of Guibemantis methueni from Andasibe and Besariaka. (A–B) ZSM 3223/2012, (ZCMV 14089) from Andasibe. (C–D) ZSM 391/2004 (ZCMV 933) from Besariaka. (E–F) Specimen from Besariaka that cannot be reliably assigned to a voucher specimen and is assigned to G. methueni based on morphology.

FIGURE 11. Dorsal and ventral views of preserved holotypes of new Guibemantis species: A–B. Guibemantis rianasoa sp. nov. (sp. Ca14), male holotype ZSM 149/2022 (ZCMV 13705); C–D. Guibemantis ambakoana sp. nov. (sp. Ca3), male holotype ZSM 152/2022 (ZCMV 13707); E, F. Guibemantis vakoa sp. nov. (sp. Ca8), male holotype ZSM 389/2004 (ZCMV 931).