Rhombophryne diadema, Scherz, Mark D., Hawlitschek, Oliver, Andreone, Franco, Rakotoarison, Andolalao, Vences, Miguel & Glaw, Frank, 2017

Scherz, Mark D., Hawlitschek, Oliver, Andreone, Franco, Rakotoarison, Andolalao, Vences, Miguel & Glaw, Frank, 2017, A review of the taxonomy and osteology of the Rhombophryne serratopalpebrosa species group (Anura: Microhylidae) from Madagascar, with comments on the value of volume rendering of micro-CT data to taxonomists, Zootaxa 4273 (3), pp. 301-340 : 318-321

Rhombophryne diadema sp. nov.

Suggested common name: Diadem saw-browed diamond frog ( Figs 4 , 5 , 11 , 12 , S8)

Holotype. ZSM 1629 /2012 ( FGZC 3604 ), adult female, collected between the 26th and 30th of November by F. Glaw, O. Hawlitschek, T. Rajoafiarison, A. Rakotoarison, F.M. Ratsoavina, and A. Razafimanantsoa on the Sorata Massif at 13.6817°S, 49.4411°E, at 1339 m a.s.l., in the Sava Region , northeastern Madagascar ( Figs 4 , 5 , S8).

Paratypes. ZSM 1628 /2012 ( FGZC 3731 ), adult male, and UADBA-A 60289 ( FGZC 3611 ), adult female with large eggs, same data as holotype except collected at a creek above the campsite in Sorata (13.6780°S, 49.4404°E) at 1407 m a.s.l.

Diagnosis and comparisons. A species assigned to the genus Rhombophryne on the basis of molecular phylogenetic affinities ( Fig. 3 ), and the possession of a clavicle combined with the absence of T- or Y-shaped terminal phalanges (vs. either absence of a clavicle or possession of a clavicle combined with T- or Y-shaped terminal phalanges in the morphologically similar Plethodontohyla ). Within the genus Rhombophryne , it is assigned to the R. serratopalpebrosa group on the basis of possessing superciliary spines and molecular phylogenetic data ( Fig. 3 ).

Rhombophryne diadema sp. nov. is distinguished from all congeners by the following unique suite of characters: SVL 22.7–23.4 mm; tympanum indistinct, TDH/ED = 0.59–0.64); weak supratympanic fold extending from the rear corner of the eye over and behind tympanum toward the axilla; three superciliary spines, the posterior-most considerably smaller than the anterior two; unreduced fingers, second finger distinctly shorter than fourth; tibiotarsal articulation reaching eye; TIBL/SVL = 0.44–0.46; and fifth toe distinctly shorter than third. Osteologically, it is characterised by an anteriorly broadening parasphenoid cultriform process, prechoanal portion of vomer non-radiate, postchoanal portion straight, broad quadratojugal-squamosal contact, stepped anterior edge of ventral ramus of squamosal, short humeral crista ventralis, weak dorsal prominence on iliac shafts, and partially ossified pubis. Additionally, R. diadema is separated from all other Rhombophryne species for which molecular data are available by uncorrected pairwise distances of at least 5.1% in a segment of the 16S rRNA mitochondrial gene ( Table 1).

Within the genus Rhombophryne , R. diadema sp. nov. differs from all species except members of the R. serratopalpebrosa group by the possession of superciliary spines. Within the R. serratopalpebrosa group, it differs from R. serratopalpebrosa by smaller size (SVL 22.7–23.4 vs. 28.5 mm), smaller relative tympanum size (TDH/ED = 0.59–0.64 vs. 0.78), a weak (vs. strong) supratympanic fold, three superciliary spines (vs. four), shorter relative forelimb length (FORL/SVL 0.59 vs. 0.71), and shorter relative hindlimb length (HIL/SVL = 1.66 vs. 1.77); from R. vaventy by much smaller size (SVL 22.7–23.4 vs. 51.9 mm), larger relative tympanum size (TDH/ED = 0.59–0.64 vs. 0.46), narrower head (HW/HL = 1.46–1.59 vs. 1.70), a weak (vs. distinct) supratympanic fold (see Fig. 5 ), three (vs. four) superciliary spines, tibiotarsal articulation reaching eye (vs. beyond snout tip), shorter relative forelimb length (FORL/SVL = 0.59 vs. 0.76), smaller relative tibia size (TIBL/SVL = 0.44–0.46 vs. 0.53), and smaller inner metacarpal tubercle size (IMCL/HAL 0.13–0.14vs. 0.19); from R. guentherpetersi by smaller size (SVL 22.7–23.4 vs. 27.5–35.1 mm), three superciliary spines, the anterior two of which are of medium size, the posterior-most of which is considerably smaller (vs. two to three small superciliary spines), broader head (HW/HL = 1.46–1.59 vs. 1.34–1.41), tibiotarsal articulation reaching the eye (vs. reaching the insertion of the arms), longer relative tibia length (TIBL/SVL 0.44–0.46 vs. 0.32–0.36), partially ossified pubis (vs. unossified), and broader pectoral girdle (compare Fig. 7 b with Fig. 12 b); from R. ornata by smaller size (SVL 22.4–23.4 mm vs. 33.0 mm), a weak (vs. distinct) supratympanic fold, three superciliary spines (vs. two), longer relative hindlimb length (HIL/SVL = 1.66 vs. 1.45–1.63), smaller relative inner metacarpal tubercle length (IMCL/HAL = 0.13–0.14 vs. 0.15–0.19), absence of reddish colour on the hidden portions of the legs (vs. presence), and ossified carpals and limb bone epiphyses (vs. unossified); from R. tany , which it most strongly resembles, by its weaker supratympanic fold (see Fig. 5 and compare Figs 1 d and 11), three superciliary spines (vs. two), slightly shorter forelimbs (FORL/SVL 0.59 vs. 0.63), slightly longer relative tibia length (TIBL/SVL 0.44–0.46 vs. 0.43), prootics in contact with parasphenoid alae (vs. not in contact), parasphenoid cultriform process broadening anteriorly (vs. having parallel edges), nasals not anterolaterally displaced (vs. displaced), quadratojugal-squamosal contact broad (vs. narrow), anterior edge of ventral ramus of squamosal distinctly stepped (vs. weakly stepped), dorsal prominence of iliac shafts weak (vs.

strong), and partially ossified pubis (vs. unossified); from R. regalis by anterior-most superciliary spine sitting atop eye (vs. anterior to eye; see Fig. 5 and compare Figs 9 and 11 ), slightly shorter relative forelimb length (FORL/SVL = 0.59 vs. 0.59–0.70), shorter relative tibia length (TIBL/SVL 0.44–0.46 vs. 0.47–0.56), tibiotarsal articulation reaching the eye (vs. reaching the snout tip or beyond), exoccipitals ventromedially not in contact (vs. in contact), anterior edge of ventral ramus of squamosal stepped (vs. smoothly sigmoidal), dorsal prominence of iliac shafts weak (vs. strong), and partially ossified pubis (vs. ossified); and from R. coronata , which it also closely resembles, by much smaller size of the posterior-most superciliary spine (vs. three roughly equal-sized superciliary spines), larger relative tympanum size (TDH/ED 0.59–0.64 vs. 0.37–0.59), longer relative tibia length (TIBL/SVL 0.44–0.46 vs. 0.35–0.39), first toe unreduced (vs. sometimes reduced to a short nub; see Fig. 5 ), anterior edge of squamosal ventral ramus stepped (vs. straight), and sphenethmoids not exceeding postchoanal vomers (vs. exceeding postchoanal vomers).

Description of the holotype. ( Figs 4 , 5 ) An adult female specimen in a very good state of preservation. Tissue taken from the left thigh for genetic sequencing. A transverse incision present in the posterior abdomen.

Body robust. Head wider than long (HW/HL = 1.59). Pupils round. Snout rounded in dorsal and lateral views. Canthus rostralis concave. Loreal region slightly concave. Nostril nearer to snout tip of than to eye (END/NSD = 0.47), directed laterally, slightly protuberant. Internarial distance greater than distance from eye to nostril. Tympanum indistinct, TDH/ED = 0.64. Supratympanic fold weak, extending from the middle back of the eye over and behind the tympanum toward the axilla. A small granular bump is present posteroventral to both tympana. Three superciliary spines above each eye, the anterior two roughly equal in size, the posterior-most almost imperceptible without magnification. Vomerine teeth present, in straight rows either side of the palate, separated medially by a small gap. Tongue broad and unlobed, attached anteriorly.

Arms fairly slender. Fingers not reduced. Fingers without webbing; relative lengths 1<2<4<3; fourth finger distinctly longer than second. Finger tips not enlarged. Nuptial pads absent; inner metacarpal tubercle present, outer metacarpal tubercle absent, subarticular tubercles weak. Hindlimbs strongly built. Tibiotarsal articulation reaches the eye; TIBL/SVL = 0.46. Inner metatarsal tubercle present; outer metatarsal tubercle absent. Toes unwebbed; relative lengths 1<2<5<3<4; fifth toe distinctly shorter than third. Dorsal skin granular, rugose in life. Dorsolateral folds absent.

Colouration of the holotype: After two and a half years in preservative, dorsal body colour is dark brown flecked with black—in life, the body was a more reddish brown ( Fig. 11 a). The posterior half is lighter in colour than the anterior, particularly around the midline. Two light-brown lines run posteromedially from the eyes, approaching one another toward the midline but ending in the suprascapular region. These lines merge anterolaterally at the posterior of the eye with the lighter flank colouration, extending onto the lateral portions of the head. A whitish line runs from the posterior edge of the eye to the corner of the mouth. The arms are dorsally light brown flecked with black. The legs are dorsally light brown, with one dark crossband on the thigh, two on the shank—the proximal of which is less distinct than the distal—one on the tarsus, one on the metatarsals, and some black spots on the toes.

The ventral surface is cream, with a little brown speckling on the chin and below the insertions of the arms. The legs are ventrally flecked with light brown and cream. The iris is gold with black reticulations and a black periphery.

Variation. Morphologically, ZSM 1628/2012 agrees strongly with the holotype. Its tympanum is slightly smaller (TDH/ED = 0.59), and its tibia shorter (TIBL/SVL = 0.44). Its colouration is starkly different, however. Dorsally, it is uniformly an earthy brown. Crossbands on the shanks are faint but present, as is the light line running between the corner of the mouth and the posterior of the eye. Based on colour photographs ( Fig. 11 ), UADBA-A 60289, which is female, also closely agrees in morphology with the rest of the type material. Its colouration is roughly intermediate between the other specimens, its dorsum being muddy brown flecked with white and black spots; a pair of small white spots being present between the anterior edges of the eyes, and again between the posterior edges, as well as over the suprascapular region. Its inguinal region is a yellowish cream. The crossbands on its legs are as in the holotype.

Etymology. The specific epithet diadema is the latinized Greek word for diadem, a small crown typically worn by female royalty. It refers to the superciliary spines borne by this species. It is a feminine nominative singular noun in apposition.

Natural history. Individuals of this species were captured when active during the day jumping among the leaflitter or near pitfall traps, suggesting a terrestrial, possibly partially fossorial lifestyle. The holotype contained at least 13 well-developed, yellow eggs (diameter 2.45 ± 0.25 mm), suggesting that the species was reproductively active at the end of November, around the start of the rainy season.

The montane rainforest of Sorata is under high human-disturbance pressure, especially due to the high number of zebu cattle, which are responsible for widespread forest disturbance in the area. The area where the specimens of this species were discovered was exceptionally intact, with dense leaf litter.

Distribution and conservation status. This species is known only from high altitudes (1339–1407 m a.s.l.) in the forest of the Sorata Massif in northern Madagascar ( Fig. 8 ). This forest is unprotected and therefore threatened by deforestation and degradation without restriction. Additionally, species at high altitude may be threatened by climate change (Raxworthy 2008; Raxworthy et al. 2008), although this threat is most likely less imminent than that of deforestation. If this species is restricted to the Sorata Massif, then its extent of occurrence and optimistically estimated area of occupancy constitutes an area of only ~ 250 km 2 (calculated in Google Earth® Pro 6.1.0.500, Google Inc., Mountain View, CA). Due to its likely restriction to a small area of unprotected forest that is under threat from deforestation and possible long-term threat of climate change, R. diadema sp. nov. qualifies as Endangered under the IUCN Red List Criteria (2012) B1ab(iii) as defined for R. guentherpetersi above, similar to R. longicrus , which was described from the same area ( Scherz et al. 2015b).

Figures

FIGURE 1. Four of the named species from the Rhombophryne serratopalpebrosa group. (a) R. ornata, (b) R. vaventy, (c) R. coronata, and (d) R. tany. No photos in life of R. serratopalpebrosa are available. Rhombophryne guentherpetersi is shown in Fig. 6.

FIGURE 3. Majority-rule consensus tree of the Rhombophryne serratopalpebrosa species group and its sister clade, obtained by partitioned BI analysis, based on 2491 nucleotide characters of two mitochondrial and one nuclear gene (16 S, cox 1, sacs). Asterisks indicate Bayesian posterior probability values (* 0.95 – 0.98, ** 0.99 – 1.0; not shown if <0.95). Stumpffia psologlossa and other species of Rhombophryne were used as hierarchical outgroups and are here excluded from the figure as they are not the subject of this study. Members of the R. serratopalpebrosa species group are depicted in life, not to scale.

FIGURE 4. Photographs of the holotypes of the species treated in this manuscript, in dorsal (top row) and ventral (bottom row) views.

FIGURE 5. Comparative morphology of the heads, feet, and hands of members of the Rhombophryne serratopalpebrosa species group. All specimens are the holotypes of their respective species, except R. coronata, which is paratype ZSM 694 / 2001. Asterisks indicate mirrored images. Not to scale.

FIGURE 7. Osteology of Rhombophryne guentherpetersi (MNHN 1953.165). Full skeleton in (a) dorsal, (b) ventral, and (c) lateral view; skull in (d) dorsal, (e) ventral, and (f) lateral view. Abbreviations: angspl = angulosplenial, col = columella, exoc = exoccipital, fpar = frontoparietal, max = maxilla, mmk = mentomeckelian, npl = neopalatine, pmx = premaxilla, povom = postchoanal vomer, proot = prootic, prvom = prechoanal vomer, prsph = parasphenoid, pter = pterygoid, qj = quadratojugal, smax = septomaxilla, spheth = sphenethmoid, sq = squamosal.

FIGURE 8. Map of the north of Madagascar showing the collection localities of specimens of the focal species of this paper, Rhombophryne guentherpetersi, R. regalis sp. nov., and R. diadema sp. nov. Basemap from www. vegmad. org. Hashing indicates protected areas; note that the full extent of Tsaratanana Strict Nature Reserve is not shown.

FIGURE 9. Rhombophryne regalis sp. nov. in life, showing the holotype (MRSN A 4602) in (a) dorsal and (b) ventral view; paratype MRSN A 4603 in (c) dorsolateral and (d) ventral view; and (e) an individual from Ambolokopatrika in dorsolateral view (assignment to field and collection numbers unknown).

FIGURE 11. Rhombophryne diadema sp. nov. in life, showing the holotype ZSM 1629 / 2012 in (a) dorsal and (b) ventral view; paratype ZSM 1628 / 2012 in (c) lateral and (d) ventral view; and paratype UADBA-A 60289 in (e) lateral and (f) ventral view.

FIGURE 12. Osteology of Rhombophryne diadema sp. nov. (ZSM 1629 / 2012). Full skeleton in (a) dorsal, (b) ventral, and (c) lateral view; skull in (d) dorsal, (e) ventral, and (f) lateral view. Abbreviations as in Fig. 7.