Bioacoustics of Rhombophryne savaka

Definition. Within the R. testudo group, this species is sister to R. mangabensis 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) small body size, adult SVL 18.8–20.9 mm ; (2) head wider than long ( HW / HL 1.66–1.80); (3) moderately small eyes ( ED / HL 0.35–0.43); (4) short hindlimbs ( HIL / SVL 1.37–1.55); (5) small inner metatarsal tubercle ( IMTL / FOL 0.11–0.14); (6) moderately distinct outer metatarsal tubercle; (7) second finger roughly equal in length to fourth, except in one individual where it is much shorter than fourth; (8) third toe distinctly longer than fifth; (9) dorsal skin finely granular with a few scattered warts, especially a suprascapular pair outlined in black; (10) absence of chin barbels; (11) absence of pronounced superciliary spines; (12) occasional presence of small black inguinal ocelli without light outline; (13) absence of distinctive markings along the posterior thigh; (14) unfortified skull without expansion of maxilla or posterior process of angulosplenial; (15) clavicles present, thin, curving; and (16) advertisement call (based on 28 analysed calls by one individual) tonal, with (17) call duration 121–142 ms, (18) inter-call interval 221–395 ms, and (19) dominant frequency 3714–3861 Hz. Rhombophryne savaka 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 ’, ‘ C’ at site 355, ‘ G’ at site 664 and ‘ T’ at site 687; in 16 S 3 ’, ‘ A’ at site 937, ‘ T’ at site 1094, and ‘ T’ at site 1155.

Call. The advertisement call recorded on 2 December 2016 at Camp 1, Marojejy National Park (call voucher ZSM 519/2016 [ MSZC 0319 ]; air temperature 22.6 ° C) during rainfall, consists of a tonal note of short duration emitted in short regular call series (Fig. 23 ). Inter-call intervals within call series tend to be slightly longer in duration towards the end of a series. Each call exhibits some slight amplitude modulation, with call energy moderately fast increasing towards the middle of the call, then keeping the same level of energy until the last quarter of the call’s duration when it quickly drops towards the call’s end. Slight upward frequency modulation is evident in each call until two thirds of the call’s duration, followed by a slight terminal drop in frequency. Numerical parameters of 28 analysed calls are as follows: call duration (= note duration) 121–142 ms (132 ± 5 ms); inter-call intervals within regular call series 221–395 ms (296 ± 45 ms); number of calls per call series 4–5 (4.3 ± 0.5); duration of regular call series 1342–1883 ms (1483 ± 187 ms); dominant frequency 3714–3861 Hz (3807 ± 47 Hz); prevalent bandwidth 1600–7800 Hz; frequency bands recognizable at approximately 1900, 5700, and 7680 Hz. Additional calls recorded on 2 December 2016 at the same locality (voucher specimen KU 347465 [ CRH 1653 ]) completely agree in general characteristics with the call described above, except for a slightly higher dominant frequency explainable by smaller body size of the calling male, and have the following numerical parameters (3 call series and 13 calls analysed): call duration (= note duration) 110–122 ms (115 ± 3 ms); inter-call intervals within regular call series 302–451 ms (340 ± 46 ms); number of calls per call series 4–5 (4.3 ± 0.6); duration of regular call series 1461–1932 ms (1631 ± 261 ms); dominant frequency 4144–4210 Hz (4175 ± 27 Hz); prevalent bandwidth 1800–8500 Hz.