Rhombophryne sp. ‘Ivohibe’

Figures 2, 4 –7, 67 –69, 76

Remark.

This population has been reported as ‘ Plethodontohyla serratopalpebrosa ’ by Raxworthy and Nussbaum (1996) and Raselimanana (1999). No genetic or bioacoustic data are available from it, and despite some morphological differences to all known species in the genus, we here refrain from describing it as a new species until new material is collected and its genetic affinities have been clarified.

Available material.

UADBA 17419 (APR 01644), UADBA 17420 (APR 1660), two adult females, and UADBA 17421 (APR 01663), UADBA 17422 (APR 01677), UADBA 17423 (APR 01770), UADBA 17424 (APR 01771), UADBA 17430 (APR 01784), five unsexed adults, all collected between 14 October and 2 November 1997 in the Reserve Spécial Pic d’Ivohibe (22.4833°S, 46.9694°E, ca 1200 m a. s. l.), Ihorombe Region, South Central Eastern Madagascar, by A. P. Raselimanana; UADBA 17425 (APR 01853), an unsexed adult, collected at 16: 00 h on 2 November 1997 in the corridor between Andringitra and Pic d’Ivohibe (22.4175°S, 46.8858°E, ca 1200 m a. s. l.), Ihorombe Region, central eastern Madagascar, by A. P. Raselimanana.

Circumscription.

Morphologically, this species shows the following suite of characters: (1) small to medium body size, adult SVL 21.6–25.8 mm; (2) head wider than long (HW / HL 1.34–1.59); (3) moderately large eyes (ED / HL 0.33–0.43); (4) relatively long hindlimbs (HIL / SVL 1.66–1.89); (5) small inner metatarsal tubercle (IMTL / FOL 0.08–0.10); (6) outer metatarsal tubercle absent; (7) second finger distinctly shorter than fourth; (8) third toe distinctly longer than fifth; (9) dorsal skin shagreened; (10) absence of chin barbels; (11) presence of three to four pronounced superciliary spines, the longest being centrally over the eye; (12) absence of inguinal ocelli or spots; (13) absence of distinctive markings along the posterior thigh; (14) unfortified skull without expansion of maxilla or posterior process of angulosplenial; and (15) clavicles present, thin, curving.

Thus, this species can easily be distinguished from all species except other Rhombophryne except members of the R. serratopalpebrosa species group by the presence of distinct superciliary spines. It differs from R. serratopalpebrosa and R. regalis by the absence of an S-shaped dermal postnasal fold; from R. regalis by the longest superciliary spine being over the centre of the eye (vs the anterior-most spine in R. regalis); from R. guentherpetersi by the absence of large, swollen tibial glands (vs presence); from R. coronata by longer hindlimb (HIL / SVL 1.66–1.89 vs 1.28–1.43), first toe unreduced (vs usually reduced), superciliary spines varying in length (vs small and equally sized), and shagreened dorsal skin (vs finely granular), and sphenethmoid not appreciably extending anterior to the postchoanal vomer (vs extending anteriorly); from R. vaventy by much smaller adult body size (SVL 21.6–25.8 mm vs> 50 mm); from R. ornata by smaller adult body size (SVL 21.6–25.8 mm vs up to 33 mm), three to four superciliary spines (vs two), and probable absence of reddish orange colouration in the inguinal region and on the thigh (vs presence); from R. tany by longer hindlimb (HIL / SVL 1.66–1.89 vs 1.56), and three to four superciliary spines (vs two); and from R. diadema possibly by more shagreened dorsal skin and more distinct supratympanic fold, by the longest superciliary spine being over the centre of the eye (vs anterior two spines equal in length and posterior-most diminutive).

Generalised morphological description.

SVL 21.6–25.8 mm (n = 8); for variation in other measurements, see Table S 10. Body rhomboid, head rather triangular. Head wider than long, eyes fairly large, pupils small, round. Snout slightly pointed in dorsal and truncate in lateral view. Canthus rostralis distinct, concave. Loreal region concave, oblique, with no trace of an S-shaped curve posterior to the nostril. Nostril nearer to tip of snout than to eye, slightly protuberant. Tympanum indistinct, round. Supratympanic fold distinct, strongly raised, partly melanised, curving gently from posterior corner of eye over tympanum toward anterior insertion of the forearm. Lateral head similar in colour to dorsal head. Three to four distinct superciliary spines above each eye, the longest over the centre of the eye. Dorsal skin shagreened in most specimens. Ventral skin smooth. Tongue quite narrow, broadening posteriorly, attached anteriorly, posteriorly free, not lobed. Maxillary and vomerine teeth present, vomerine teeth rather straight, without any variation in height, separated from one another at the midline by a small gap. Choanae oval, placed laterally in the roof of the mouth, slightly melanised.

Forelimbs rather long, slender. Fingers without webbing, relative lengths 1 <2 <4 <3, second finger distinctly shorter than fourth. Finger tips not expanded, rounded. Finger subarticular tubercles indistinct; inner metacarpal tubercle small, weakly developed, greyish, outer metacarpal / palmar tubercle indistinct, greyish, single. Hind limb slender. Inner metatarsal tubercle present, oblong, greyish, weakly raised. Outer metatarsal tubercle absent. Toes not webbed; toes unreduced, toe lengths 1 <2 <5 <3 <4, fifth toe distinctly shorter than third; subarticular tubercles indistinct, grey; toe tips not enlarged, slightly pointed, especially fourth toe.

The base colour is a dark brown across the dorsum and flanks, including the dorsal limbs. The dorsum has several nearly black markings on it in all individuals, but vary in intensity; some individuals have lines that run slightly discontinuously from the suprascapular region toward the inguinal region roughly parallel to one another. No distinct inguinal spots present, no traces of cream-bordered markings present. No distinct colour difference between the lateral and dorsal head. The supratympanic fold is blackish above the tympanum, but otherwise dark brown. The hindlimbs lack distinct crossbands, but a concentration of these blackish markings on the mid-shank gives the impression of a crossband. The posterior thigh is not distinctly coloured. The foot is laterally dark brown, but medially creamy brown. A cream annulus is present before the terminal phalange of each finger and toe. The ventral foot is dark brown, fading to grey along the toes. No distinct colouration around the cloaca. The arms have several blacking markings, including a moderately large marking in the middle of the antebrachium. The dorsal hand is lighter medially than laterally; the ventral hand is light brown. The chin is mottled light brown with tan flecks, fading to completely tan over the sternal region into the immaculate abdomen.

Distribution.

Specimens referred to this putative candidate species are from (1) the Pic d’Ivohibe Special Reserve (type locality), and (2) the corridor between Ivohibe and Andringitra. Raxworthy and Nussbaum (1996) recorded specimens probably referrable to this species at 1625 m a. s. l. in Andringitra National Park, but also gave it a range from 1240 to 1300 m a. s. l. in the same table; it is not clear which range is correct, but the latter better matches the specimens discussed here. Elevation: ca 1200–1275 m a. s. l.

Natural history.

This is a semi-fossorial or detriticolous species found in mid-elevation humid forest. Specimens of this species were caught in pitfall traps and on surveys by Raselimanana (1999). During the day they hide under thick leaf litter or under rotten logs. An individual (UADBA 17422, APR 01677) was found under a rotten log with tadpoles at 16: 00 h in primary rain forest on a ridge. Regrettably, both the tadpoles and data pertaining to them have been lost.