Bioacoustics of Mantidactylus riparius

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.

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).

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.