Mantidactylus riparius, Scherz & Crottini & Hutter & Hildenbrand & Andreone & Fulgence & Köhler & Ndriantsoa & Ohler & Preick & Rakotoarison & Rancilhac & Raselimanana & Riemann & Rödel & Rosa & Streicher & Vieites & Köhler & Hofreiter & Glaw & Vences, 2022

Scherz, Mark D., Crottini, Angelica, Hutter, Carl R., Hildenbrand, Andrea, Andreone, Franco, Fulgence, Thio Rosin, Köhler, Gunther, Ndriantsoa, Serge Herilala, Ohler, Annemarie, Preick, Michaela, Rakotoarison, Andolalao, Rancilhac, Loïs, Raselimanana, Achille P., Riemann, Jana C., Rödel, Mark-Oliver, Rosa, Gonçalo M., Streicher, Jeffrey W., Vieites, David R., Köhler, Jörn, Hofreiter, Michael, Glaw, Frank & Vences, Miguel, 2022, An inordinate fondness for inconspicuous brown frogs: integration of phylogenomics, archival DNA analysis, morphology, and bioacoustics yields 24 new taxa in the subgenus Brygoomantis (genus Mantidactylus) from Madagascar, Megataxa 7 (2), pp. 113-311 : 235-237

Mantidactylus riparius sp. nov.

Identity and justification.—This lineage of the M. betsileanus clade was first discovered by Cocca et al. (2018) and named ‘ Mantidactylus sp. aff. multiplicatus Ca 65 “Isalo”’. It was not included in earlier DNA barcoding assessments of Madagascar’s anuran diversity. It represents the third Brygoomantis species occurring in the Isalo massif, besides M. mahery and M. noralottae . Both this lineage and M. noralottae have so far only been recorded from Isalo and belong to the M. betsileanus clade according to the 16S tree. Mantidactylus kortei appears also to belong to this clade, and is morphologically and bioacoustically similar to this lineage. However, we here consider the Isalo lineage as a separate species from M. kortei due to its high genetic divergence of 5.9–6.8% in the 16S gene, absence of Rag-1 haplotype sharing and ecological divergence (found in canyons in the dry Isalo sandstone massif, vs M. kortei occurring only on high elevations in humid rainforest of Andohahela).

Holotype.— ZSM 2403/2007 ( ZCMV 5766 ), adult male, collected by L. du Preez, C. Weldon, O. Verneau, and L. Raharivololoniaina on 16 February 2007 at Isalo (Cascade des Nymphes), Ihorombe Region, Madagascar.

A 16S barcode sequence of the holotype was obtained in this study and was included in the analysis.

Paratypes.—A total of eight paratypes: ZSM 186/2021 ( ACZCV 281 , extraction ACP 2294 , tissue ACZC 6908 ) and ZSM 187/2021 ( ACZCV 283 , ACP 2296 , ACZC 6911 ), two probable females, collected on 25 November 2014 by A. Crottini, G.M. Rosa and F. Andreone at the Isalo Massif ( Andriamanero : Antsifotra canyon); UADBA uncatalogued ( ZCMV 5541 – 5544 , ZCMV 5749 , ZCMV 5775 ), six specimens of unkonwn sex and maturity, collected by L. du Preez, C. Weldon, O. Verneau, and L. Raharivololoniaina in February 2007 in the Isalo Massif .

Diagnosis.— Mantidactylus riparius sp. nov. is a member of the M. betsileanus clade and related to M. noralottae and M.kortei based on the 16S tree (not included in the phylogenomic analysis). See Table 4 for a list of diagnostic morphological characters. The combination of a relatively small body size (male SVL 27 mm), slightly tubercular dorsal skin, relatively large tympanum (13% of SVLin males), and advertisement call consisting of a single pulsed note not repeated in regular series distinguishes M. riparius sp. nov. from species of all other clades. Species of the M. fergusoni clade are larger and have typically a more tubercular dorsum, while species of the M. curtus clade are often larger and most have a smaller tympanum. Some specimens of the new species have whitish dots on the flanks and most have only an indistinct white marking on the snout tip, which impedes their distinction from some species of the M. biporus , M. stelliger and M. inaudax clades where advertisement calls are unknown. However, the usually more pointed snout, larger tympanum, longer limbs, and overall different appearance of M. riparius sp. nov. should make a distinction straightforward ( Table 4 ). Within the M. betsileanus clade, the new species can be distinguished from M. betsileanus , M. noralottae and M. tripunctatus by having fewer pulses per note in advertisement calls; furthermore from M. noralottae by smaller body size. Mantidactylus katae has a different advertisement call structure and larger femoral glands; M. jonasi has typically more pulses per note in advertisement calls, a lower pulse repetition rate, and a more tubercular dorsum; M. incognitus has more expressed dorsal and dorsolateral ridges and supraocular tubercles ( Table 4 ). The new species is most similar to the allopatric M. kortei from which it cannot be reliably distinguished by morphology or calls, despite a tendency of a faster pulse rate in advertisement calls which however might be influenced by temperature ( Table 4 ). For a detailed distinction from other new species described herein, see the respective species accounts. A full list of molecular diagnostic sites in the 16S gene of M. riparius sp. nov. in pairwise comparisons to all other Brygoomantis species is provided as Supplementary appendix.

Description of the holotype.—Adult male, in good state of preservation except for a large part of the right thigh excised for tissue sampling, and belly cut open (with some inner organs including bladder removed for parasite sampling) ( Fig. 33 ). Body slender. Head slightly wider than body. Snout rounded in lateral view, slightly pointed in dorsal view. Nostrils directed laterally, slightly protuberant, nearer to tip of snout than to eye. Canthus rostralis straight; loreal region concave. Tympanum distinct and rather large, wider than high, horizontal diameter of tympanum 82% of horizontal eye diameter.

Supratympanic fold distinct, following the outer edge of the tympanum, regularly curved. Tongue ovoid, bifid.

Maxillary teeth present. Vomerine teeth form two small roundedaggregations,positionedposterolateraltochoanae.

Choanae small and rounded. Subarticular tubercles single.

Inner and outer metacarpal tubercles present. Fingers without webbing. Relative length of fingers: I<II<IV<III.

Finger discs slightly enlarged. Nuptial pads absent. Foot slightly longer than tibia (104%). Lateral metatarsalia separated. Inner metatarsal tubercle present, small. Outer metatarsal tubercle not clearly recognisable. Webbing formula: 1(1), 2i(1.5), 2e(0.75), 3i(1.75), 3e(1), 4i(1.5), 4e(1), 5(0.5). Relative length of toes: I<II<V=III<IV.

Skin on the upper surface smooth. Ventral side smooth.

Femoral gland distinct.

Variation.—Variation in measurements is given in Table 7. See Fig. 46 for colouration in life and its variation.

Given the small sample sizes of measured individuals, an assessment of sexual dimorphism is not possible. Femoral glands in males are relatively weakly expressed and not conspicuously coloured in life.

Natural history.—Found along semi-permanent streams and in natural pools of oasis at Isalo sandstone massif. It is a relatively shy species that hides in the crevices of the rocks. The species is found in syntopy with both Mantidactylus mahery and M. noralottae .

Calls.— The advertisement call of M. riparius (FAZC 14746; ACP4528), recorded on 12 February 2011, at Isalo (Andriamanero), unknown air temperature, consisted of a pulsed note ( Fig. 47 ) of variable duration, emitted in somewhat irregular series. Notes exhibited amplitude modulation, with call energy rapidly increasing from the beginning of the note, reaching its maximum after approximately one tenth of the note’s duration, continuously decreasing afterwards. Pulse repetition rate within notes was highest at the beginning and decreases towards the note’s end. Call energy was distributed in a wide frequency band. Numerical parameters of 12 analysed calls were as follows: call duration (= note duration) 249–697 ms (348.4 ± 139.2 ms); 15–41 pulses per note (21.0 ± 8.1); pulse duration 2–5 ms (3.8 ± 1.3 ms); pulse repetition rate within notes 49.2–114.3 pulses/s (74.0 ± 27.5); dominant frequency 1518–1574 Hz (1549 ± 28 Hz); prevalent bandwidth 950–7400 Hz; call repetition rate (= note repetition rate) within series ca 5–9 calls/ min.

Tadpoles.— The tadpole of this species has not been described.

Distribution.— Apparently microendemic to the Isalo massif ( Fig. 7 ). Elevation range: 640–920 m a.s.l.

Etymology.—The Latin adjective riparius, meaning ‘inhabiting the banks of rivers’, making reference to the preferred microhabitat of this (and other) Brygoomantis species.

Figures

FIGURE 7. Mantidactylus subgenus Brygoomantis species distribution based on verified records, divided by clade (Mantidactylus stelliger sp. nov. is presented alongside the inaudax clade for practicality). Colours for species correspond to those in Figs 2 and 4. Inset map shows the geographic regions of Madagascar identified by Boumans et al. (2007), referred to throughout the text.

FIGURE 33. Preserved holotype specimens of newly named species in the M. betsileanus clade. Scale bars equal 5 mm.

FIGURE 46. Mantidactylus riparius sp. nov. from the Isalo massif in life, in dorsolateral and ventral view. (a,b) Adult male (ACZC 1849 = FAZC 14351). (c) Adult female (ACZC 1852 = FAZC 14353). (d) Adult female (ACZC 1929; yellowish oocytes visible through the skin on the flank). (e,f) Adult female (ACZC 1923 = FAZC 14366).

FIGURE 47. Audiospectrogram and corresponding oscillogram of one advertisement call of Mantidactylus riparius, recorded on 12 February 2011 at Isalo (air temperature unkown). Recording bandpass-filtered at 500–8000 Hz.