Bioacoustics of Rhombophryne proportionalis

Call. The advertisement call recorded on 15 June 2010 (11: 40 h) at Camp Bepia, Tsaratànana (air temperature unknown) from several individuals, consists of a high-pitched tonal note of short duration emitted in regular call series at regular and fast succession (Fig. 60 ). Each call exhibits slight amplitude modulation, with highest energy present at approximately the middle of the call’s duration, with few calls at the end of call series exhibiting two separated energy peaks. Slight upward frequency modulation is evident in each call. Numerical parameters of 63 analysed calls are as follows: call duration (= note duration) 27–60 ms (45 ± 8 ms); inter-call intervals within regular call series 45–88 ms (63 ± 9 ms); number of calls per call series 9–17 (13 ± 3); duration of regular call series 893–1765 ms (1323 ± 291 ms); dominant frequency 5162–5738 Hz (5461 ± 123 Hz); prevalent bandwidth 5000–6300 Hz. Calls from the same recording have been described by Scherz et al. (2019 b ) using the note-centred terminological scheme.

Definition. This species is the sole member of the R. proportionalis group and phylogenetically distinct from all other Rhombophryne 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) diminutive body size, adult SVL 11.0– 12.3 mm ; (2) head wider than long ( HW / HL 1.56–1.66); (3) comparatively large eyes ( ED / HL 0.40–0.48); (4) relatively short hindlimbs ( HIL / SVL 1.21–1.33); (5) small inner metatarsal tubercle ( IMTL / FOL 0.07–0.14); (6) outer metatarsal tubercle variably present or absent; (7) second finger equal in length to fourth; (8) third toe distinctly longer than fifth, first toe highly reduced; (9) dorsal skin smooth; (10) absence of chin barbels; (11) absence of pronounced superciliary spines; (12) presence of black inguinal spots or lines; (13) absence of distinctive markings along the posterior thigh; (14) paedomorphic skull without expansion of maxilla or posterior process of angulosplenial; (15) clavicles absent; and (16) advertisement call (based on 63 analysed calls by one individual) tonal, emitted in rapid, regular series, with (17) call duration 27–60 ms, (18) inter-call interval within series 45–88 ms (9–17 calls per series), and (19) dominant frequency 5162–5738 Hz. Rhombophryne proportionalis 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 ’, ‘ A’ at site 496, ‘ C’ at site 511, and ‘ G’ at site 547; in 16 S 3 ’, ‘ T’ at site 966, ‘ C’ at site 967, ‘ A’ at site 1013 and ‘ T’ at site 1165.