Bioacoustics of Rhombophryne laevipes

Referred specimens. ZSM 902/2003 ( FGMV 2002.0916 ), a juvenile specimen, collected on 19 February 2003 , and ZSM 925/2003 ( FGMV 2002.0998 ), an adult female , collected on 19–20 February 2003 on Montagne d’Ambre (no precise coordinates), Diana Region, northern Madagascar , by F. Glaw, R. D. Randrianiaina, and A. Razafimanantsoa; ZSM 200/2004 ( FGZC 387) and ZSM 218/2004 ( FGZC 423), a juvenile and an unsexed individual, collected on 19 February 2004 on the Voie des Milles Arbres ( 12.5200°S , 49.1756°E , 1052 m a. s. l.), Montagne d’Ambre National Park, Diana Region, northern Madagascar , by F. Glaw, M. Puente, R. Randrianiaina, A. Razafimanantsoa; ZSM 2188/2007 ( FGZC 1283 ), a juvenile, collected on 13 March 2007 near the Cascade Antakarana (ca 12.52°S , 49.17°E , ca 1030 m a. s. l.), Montagne d’Ambre National Park, Diana Region, northern Madagascar , by P. Bora; ZSM 77/2018 ( MSZC 0648 ), adult male (call voucher), collected at 14: 56 h on 19 November 2017 near the Gîte d’Étape ( 12.5204°S , 49.1718°E , 1066 m a. s. l.), Montagne d’Ambre National Park, Diana Region, northern Madagascar , by M. D. Scherz, J. H. Razafindraibe, A. Razafimanantsoa, O. Randriamalala, S. M. Rasolonjavato, R. Tiavina, and A. Rakotoarison (Fig. 32 A – C , 33 A – C); UADBA -A 62340 ( MSZC 0526 ), a subadult, collected at night on 25 December 2017 at 12.5205°S , 49.1890°E , 1028 m a. s. l. in Montagne d’Ambre National Park, Diana Region, northern Madagascar , by M. D. Scherz, J. H. Razafindraibe, A. Razafimanantsoa, O. Randriamalala, S. M. Rasolonjavato, R. Tiavina, and A. Rakotoarison (Fig. 32 D – F ); UADBA -A 62493 ( MSZC 0654 ), a juvenile, collected on 19 November 2017 at 12.5206°S , 49.1862°E , 1008 m a. s. l. in Montagne d’Ambre National Park, Diana Region, northern Madagascar , by M. D. Scherz, J. H. Razafindraibe, A. Razafimanantsoa, O. Randriamalala, S. M. Rasolonjavato, R. Tiavina, and A. Rakotoarison (Fig. 32 G – I ); UADBA -A- FGZC 1052 , individual of unknown sex or maturity, collected on 25 February 2007 on Montagne d’Ambre in a pitfall trap (precise coordinates not available), Diana Region, northern Madagascar , by F. Glaw, P. Bora, H. Enting, J. Köhler, and I. Knoll. The specimen ZSM 853/2003 ( FGMV 2002.823 ), an adult female , collected on 3 February 2003 at ‘ Camp 1 ’ ( 13.9770°S , 48.4220°E , 751 m a. s. l.), Manongarivo Massif, Diana Region, northern Madagascar , by F. Glaw, R. D. Randrianiaina, and M. Vences (Fig. 33 H – I ), is phylogenetically sister to all other specimens collected so far (Fig. 2 ), and differs genetically from all other specimens of R. laevipes by 1.24–2.46 % in the 16 S 3 ’ marker, and 4.90–5.45 % in the 16 S 5 ’ marker, but is consistently recovered as conspecific in species delimitation, and is therefore assigned to this species. A second specimen from the other side of this mountain, BMNH 1987.2300 , an unsexed adult, collected on 25 February 1988 at ‘ Camp B’ ( 14.067°S , 48.283°E , 350 m a. s. l.), Manongarivo Massif, Sofia Region, northern Madagascar , by C. J. Raxworthy, agrees morphologically, and is consequently also assigned to this species.

Call. The advertisement call recorded on 19 November 2017 (14: 30 h) near the Gîte d’Étape (air temperature 21.3 ° C; voucher specimen ZSM 77/2018 , MSZC 0648 ) consists of a low-pitched, pulsed note of moderate duration, usually emitted in short call series containing 2 or 3 calls, although one single call was also recorded (Fig. 35 ). Calls (= notes) exhibit distinct amplitude modulation, with call energy starting at low level, rapidly increasing after about a fifth of the call’s duration, reaching its maximum at about half of the call’s duration, followed by a decrease towards the call’s end. Pulses are very narrowly spaced and very short in duration, with each pulse apparently shorter than 3 ms, but difficult to measure exactly. It is also not possible to count the number of pulses per note (= call), but pulse repetition rate can roughly be calculated in major parts of the note. Numerical parameters of 12 analysed calls are as follows: call duration (= note duration) 208–254 ms (228 ± 13 ms); inter-call intervals within regular call series 1563–2186 ms (1758 ± 231 ms); number of calls per call series 2 or 3 (2.1 ± 0.3); duration of regular call series 2008–4167 ms (2632 ± 899 ms); pulse repetition rate within calls about 310–320 pulses / second; dominant frequency 612–631 Hz (619 ± 6 Hz); prevalent bandwidth 320–3000 Hz; numerous parallel frequency bands recognizable with approximately 320 Hz spacing up to 9200 Hz, which represent a reflection of pulse rate (see Köhler et al. 2017 ).

Diagnosis. Within the genus Rhombophryne , R. laevipes can easily be distinguished from R. testudo , R. coudreaui , R. matavy , and R. maraorao sp. nov . by smooth skin (vs rough), absence of chin barbels (vs presence), much longer hindlimbs ( HIL / SVL 1.62–1.86 vs 1.10–1.41), and presence of white spots in the inguinal region and on the ventral shank (vs absence); from R. mangabensis , R. mavokely sp. nov . , R. savaka , R. proportionalis , and members of the R. ellae and R. minuta species groups by much larger adult body size ( SVL 42.8–50.8 mm vs 11.0– 30.1 mm ), and presence of white spots in the inguinal region and on the ventral shank (vs absence); and from all members of the R. serratopalpebrosa species group by the absence of superciliary spines (vs presence), and presence of white spots in the inguinal region and on the ventral shank (vs absence). Within the R. laevipes species group, R. laevipes may not be distinguishable from R. nilevina morphologically (traits formerly thought to be diagnostic of the latter species are now known to be variable and overlap with R. laevipes ; see the account, below), but can be distinguished by its shorter advertisement call (call duration 208–254 ms vs 526–534 ms), much shorter inter-call interval (1.5– 2.2s vs 42–126 s), and higher dominant frequency (612–631 Hz vs 526–534 Hz). It can be distinguished from R. botabota by the presence of white spots on the inguinal region, posterior thigh, and ventral shank (vs black inguinal ocelli or absence of inguinal spots, and no remarkable colour on the hindlimbs), and pulsed (vs tonal) advertisement call that is longer (call duration 208–254 ms vs 161–201 ms) and lower in dominant frequency (612–631 Hz vs 1256–1291 Hz). For distinction from newly described members of this species group, see their respective descriptions below.

Definition. Within the R. laevipes group, this species has a rather isolated position, and is probably sister to a subclade containing various other species based on molecular phylogenetic data (Fig. 2 ; Belluardo et al. 2022 ). It is characterised by the possession of the following unique suite of characters: (1) large body size, adult SVL 42.8–50.8 mm ; (2) head wider than long ( HW / HL 1.57–1.84); (3) moderately small eyes ( ED / HL 0.30–0.34); (4) relatively long hindlimbs ( HIL / SVL 1.62–1.86); (5) small inner metatarsal tubercle ( IMTL / FOL 0.08–0.11); (6) outer metatarsal tubercle absent; (7) second finger shorter than or equal in length to fourth; (8) third toe distinctly longer than fifth; (9) dorsal skin smooth with very few raised bumps in some individuals; (10) absence of chin barbels; (11) absence of pronounced superciliary spines; (12) presence of white inguinal spots on a dark brown background; (13) presence of white spots on the posterior thigh and ventral surface of the shanks; (14) unfortified skull without expansion of maxilla or posterior process of angulosplenial; (15) clavicles present, thin, curving; and (16) advertisement call (based on 12 analysed calls by one individual) highly pulsed, with (17) call duration 208–254 ms, (18) inter-call interval 1563–2186 ms, and (19) dominant frequency 612–631 Hz. Rhombophryne laevipes is furthermore distinguished from all other Rhombophryne species analysed by the following robust diagnostic nucleotide combination in the mitochondrial 16 S rRNA gene (positions relative to the full 16 S sequence of Anilany helenae MZ 751042 ): in 16 S 5 ’, ‘ T’ at site 354, ‘ G’ at site 395, and ‘ C’ at site 611; in 16 S 3 ’, ‘ G’ at site 1075, ‘ T’ at site 1086, and ‘ G’ at site 1165.

Natural history. Rhombophryne laevipes is a semi-fossorial or detriticolous species found in low- to mid-elevation humid forest. Males call during and shortly after rain, especially at night, from concealed positions within the leaf litter. Between November 2017 and January 2018 , calling activity was greatest at the start of November, and diminished as rain frequency increased. This suggests that mating may take place at the start of the rainy season. When handled, captured males that had been calling struggled to deflate their vocal sacs, and emitted distress calls. Juvenile and subadult individuals were more commonly encountered than adults, usually active at night. After capture, we spent a short time observing the behaviour of ZSM 77/2018 . Its initial escape attempts were long leaps. After calming down, when placed in leaf litter, it did not attempt to dig backwards, as is thought to be the dominant mode of digging in Rhombophryne . Instead, it attempted to hide by pushing itself under objects head-first, using its strong hindlimbs to push its body forward (Fig. 33 C ). Eudeline et al. (2015 ) reported on the predation of this species by Compsophis albiventris .