Rhombophryne ellae, Scherz, 2020

Scherz, Mark D., 2020, Diamond frogs forever: a new species of Rhombophryne Boettger, 1880 (Microhylidae, Cophylinae) from Montagne d'Ambre National Park, northern Madagascar, Zoosystematics and Evolution 96 (2), pp. 313-323 : 313

Rhombophryne ellae sp. nov. Figures 1 , 2 , 3

Holotype.

ZSM 76/2018 (MSZC 0534), adult or subadult female, collected on 28 December 2017 in Montagne d’Ambre National Park (12.5066°S, 49.1746°E, 892 m a.s.l.), Antsiranana Region, northern Madagascar by M. D. Scherz, J. H. Razafindraibe, A. Razafimanantsoa, O. Randriamalala, S. M. Rasolonjavato, R. Tiavina, E. Z. Lattenkamp, and A. Rakotoarison.

Diagnosis.

Rhombophryne ellae sp. nov. is assigned to the genus Rhombophryne based on its plump body shape, presence of vomerine and maxillary teeth, curved clavicle, knob-shaped terminal phalanges, and phylogenetic relationships. It is distinguished by the following unique combination of characters: (1) adult or subadult female SVL 24.9 mm, (2) distinctly enlarged inner metatarsal tubercle, (3) absence of superciliary spines, (4) orange flash-markings on its posterior thighs in life, and (5) presence of large and distinct black inguinal spots.

The new species can be distinguished from all described members of the genus Rhombophryne by the orange colouration on its posterior thighs. Additionally, it may be distinguished from all members of the Rhombophryne serratopalpebrosa species group ( R. serratopalpebrosa ( Guibé, 1975), R. guentherpetersi , R. coronata (Vences & Glaw, 2003), R. vaventy Scherz, Ruthensteiner, Vences & Glaw, 2014, R. ornata , R. tany Scherz, Ruthensteiner, Vieites, Vences & Glaw, 2015, R. diadema Scherz, Hawlitschek, Andreone, Rakotoarison, Vences & Glaw, 2017, and R. regalis Scherz, Hawlitschek, Andreone, Rakotoarison, Vences & Glaw, 2017) with ease by absence of superciliary spines; from R. testudo , R. matavy , and R. coudreaui by smoother dorsal skin, a longer and less broad head (HW/HL 1.48 vs 1.88-2.42), relatively longer legs (HIL/SVL 1.77 vs 1.17-1.41), and less-developed inner metatarsal tubercle; from R. savaka and R. mangabensis by its longer forelimb (FORL/SVL 0.55 vs 0.41-0.48), longer hindlimb (HIL/SVL 1.77 vs 1.49-1.60), and less broad head (HW/HL 1.48 vs 1.54-1.86); and from R. minuta and R. longicrus by its shorter hindlimb (HIL/SVL 1.77 vs 1.79-1.84), shorter forelimb (FORL/SVL 0.55 vs 0.70-0.75), and wider head (HW/HL 1.48 vs 1.22-1.43). Morphologically, Rhombophryne ellae sp. nov. is similar to R. laevipes , R. nilevina Lambert, Hutter & Scherz, 2017, and R. botabota Scherz, Glaw, Vences, Andreone & Crottini, 2016, especially young individuals, but in addition to large genetic distances, it differs by absence of ocelli on the hidden portions of the legs (vs presence), presence of large black inguinal spots (vs absence), and absence of distinct colouration of the lateral surface of the head (vs presence in R. botabota and some R. laevipes ), and also in its smaller body size from R. laevipes and R. nilevina (presumed adult female SVL 24.9 mm vs at least 28.6 mm and generally > 30 mm).

Rhombophryne ellae sp. nov. is also distinguished from all described Rhombophryne species by an uncorrected p-distance of > 7.1% in a fragment of the 16S rRNA gene (Table 1 ; Appendix II).

The new species can also be distinguished from all known members of the morphologically similar but not closely related genus Plethodontohyla on the basis of the orange colouration on its posterior thighs.

Holotype description.

Morphology. An adult or subadult female specimen in a good state of preservation, its hindlimbs and toe tips slightly dehydrated. Tissue samples taken from left thigh for sequencing. A small incision is present on the right side and in the wall of the gut. Developing eggs are visible in the ovaries, and the oviduct is thick and white.

Body robust. Head wider than long (HW/HL = 1.48). Pupils more or less round. Snout rounded in dorsal and lateral view. Canthus rostralis distinct, concave. Loreal region concave, without dermal folds. Nostrils nearer to snout tip than to eye (END/NSD = 0.87), directed laterally, slightly protuberant. Tympanum distinct, TDH/ED = 0.6. Supratympanic fold distinct, rounded over the tympanum from the posterior corner of the eye, ending anterior to the insertion of the forelimb. Superciliary spines absent. Vomerine teeth distinct, in a straight row on either side of the palate, varying in height, approaching each other medially but separated by a small gap. Choanae diminutive, unusually close to the neopalatine.

Arms rather slender. Fingers without webbing, relative lengths 1<4<2<3; fourth finger slightly shorter than second; finger tips not expanded; fingers not reduced (Fig. 2c ); nuptial pads absent; inner metacarpal tubercle present, outer metacarpal tubercle absent; subarticular tubercles round and flat, undivided. Hindlimbs fairly slender (also in life, not an artefact of preservation); tibiotarsal articulation reaches the eye when the hindlimb is adpressed forward along the body; TIBL/SVL = 0.46. Inner metatarsal tubercle present, round, slightly enlarged, outer metatarsal tubercle present, rather weak, distinct, round. Toes unwebbed; relative lengths 1<2<5<3<4, fifth toe distinctly shorter than third. Toe tips not expanded, second, third, and fourth toe tips slightly pointed. Dorsal and ventral skin smooth in preservative, but with a few dispersed pustules in life (Fig. 2 ). Dorsolateral folds absent.

Colouration. After just over a year in preservative, specimen dorsally brown, with two darker spots above the suprascapulae. A faint dark brown chevron is present on the posterior portion of the dorsum. Distinct black inguinal spots present. A russet brown spot is present on the posterodorsal portion of the tympanum, which is otherwise dirty cream. On the left side of the snout there is a further lighter area that is not present on the right side. A light interocular bar is present. The dorsal hindlimbs are as the dorsum in colour, with faint, dark-grey crossbands on the thigh and shank. The feet are highly mottled with cream and grey-brown, with a whitish annulus before each toe tip. The hidden surfaces of the thigh are cream, and there is a distinct black trapezoid in the cloacal region. The forelimbs are similar to the dorsum in dorsal colourations, with a dark-grey crossband on the antebrachium, followed by a white spot distally. The hands are mottled like the feet, also with light annuli before each fingertip. Ventrally, the abdomen is translucent cream, the scapular region and chin are mottled cream and olive-brown, and the hindlimbs and forelimbs are brown, flecked with cream, forming larger blotches more distally. The soles of the hands and feet are dark-grey, mottled with cream. The subarticular and carpal and tarsal tubercles are likewise cream. Colouration in life is shown in Figure 2 .

Osteology. Skeleton resembling other Rhombophryne species ( Scherz et al. 2017a); what follows is thus a brief summary of remarkable features of the skeleton (Fig. 3 ). Frontoparietal robust, bearing dorsal processes nearly forming a ridge. Otic capsule not dorsally ossified. Nasal broad with a long and cuneate maxillary process, widely separated from the contralateral. Post-choanal vomer bearing teeth with a distinct diastema either side of the cultriform process of the parasphenoid. Parasphenoid alae nearly the breadth of its cultriform process. Neopalatine broad. Sphenethmoid strongly ossified, bounding around half the length of the braincase. Exoccipitals widely separated dorsally. Premaxilla and maxilla bearing teeth. Maxilla with a broad connection to the quadratojugal. Quadratojugal anteriorly broad, its bulbous posteroventral process thick, dorsally with broad contact to the squamosal. Squamosal with a distinctly flared ventral ramus, a nearly vertical otic ramus, and a shorter, anteromedially curving zygomatic ramus. Pterygoid anterior ramus distinctly bowed, ventral ramus very deep. Mandible robust, the receiving surface of the angulosplenial (coronoid process) somewhat laterally flared to receive the quadratojugal. Clavicle robust and curved. Coracoid slender at its midpoint. Humerus with a strong crista ventralis and a broad epicondylus ulnaris. Urostyle with a dorsal crest running circa two-thirds of its length. Ilium with a low dorsal crest and a rather shallow oblique groove. Pubis semi-ossified. Centrale of the foot large, but the prehallux is not enlarged. Terminal phalanges of fingers and toes knobbed. Prepollex short and triangular. Hand bone configuration as in the R. serratopalpebrosa species group ( Scherz et al. 2017a).

Measurements (all in mm). SVL 24.9, HW 9.6, HL 6.5, ED 2.5, END 1.3, NSD 1.5, NND 3.1, TDH 1.5, TDV 1.6, HAL 5.3, UAL 3.6, LAL 4.7, FORL 13.7, FARL 10.0, THIL 12.5, THIW 3.5, TIBL 11.5, TIBW 3.3, TARL 6.96, FOL 11.6, FOTL 18.6, HIL 42.5, IMCL 1.0, OMCL 1.1, IMTL 1.0, OMTL 0.6.

Natural history, distribution, and conservation status.

The holotype was collected at 892 m a.s.l. in rainforest on Montagne d’Ambre during the day actively jumping away from trampling feet during moderate to heavy rain brought about by Cyclone Ava. Its gut contents included three whole ants and one ant head, seemingly belonging to two different species (one of the whole ants is diminutive), the head of a jumping spider ( Salticidae ), and the elytra and other body parts of a beetle. Nothing more is known of the ecology of this species, though it is probable that its reproductive mode and ecology is similar to other litter-dwelling Rhombophryne species ( Scherz et al. 2016a). As the species is known from a single individual, its Red List status cannot be confidently estimated. However, the syntopically occurring Stumpffia species have been suggested to be Near Threatened due to their small range and presumed micro-endemicity within a well-protected forest, and this likely applies to R. ellae sp. nov. as well.

Etymology.

It is with great pleasure that I dedicate this charming little frog to my partner, Dr Ella Z. Lattenkamp, in appreciation of her love, support, and infinite patience, and in celebration of the completion of her PhD.

Available names.

No names are currently available for the family Cophylinae that could refer to this species.

Figures

Figure 1. Bayesian inference phylogeny of Rhombophryne based on concatenated sequences of the mitochondrial markers 16 S rRNA and COI (1134 bp). Values at nodes indicate percent bootstrap support (BS) / Bayesian posterior probability (PP); ' - ' indicates clades not recovered in the ML tree. Anodonthyla montana was used as outgroup (not shown for graphical reasons). Rhombophryne serratopalpebrosa is the only described species missing from this phylogeny, as no sequences of that species are available.

Figure 2. The holotype of Rhombophryne ellae sp. nov. in life. a. In dorsolateral view; b. In dorsal view; c. In ventral view; d. In posterior view showing the orange flash-markings on the thighs and the distinctive inguinal spots; e. On leaf litter.

Figure 3. Volumetric renderings of micro-CT scans of the skeleton of the holotype of Rhombophryne ellae sp. nov. (ZSM 76 / 2018). a-c. Full skeleton in (a) dorsal, (b) lateral, and (c) ventral view; d-g. Skull in (d) dorsal, (e) ventral, (f) anterior, and (g) lateral view; h. Foot in ventral view; i. Hand in ventral view. Abbreviations: angspl - angulosplenial; angspl. cp - coronoid process of the angulosplenial; col. pip - pars interna plectri of columella; col. pmp - pars media plectra of columella; exoc - exoccipital; exoc. oc - occipital condyle of exoccipital; fpar - frontoparietal; fpar. dp - dorsal process of frontoparietal; fpar. lf - lateral flange of frontoparietal; max - maxilla; max. pf - pars facialis of maxilla; mmk - mentomeckelian; nasal. mp - maxillary process of nasal; neopal - neopalatine; pmx - premaxilla; pmx. ap - ascending process of premaxilla; pmx. lp - lingual process of premaxilla; pmx. palproc - palatine process of premaxilla; povom - postchoanal portion of vomer; proot - prootic; prsph. al - parasphenoid alae; prsph. cp - cultriform process of parasphenoid; prsph. pp - posterior process of parasphenoid; prvom - prechoanal portion of vomer; pter. ar - anterior ramus of pterygoid; pter. mr - medial ramus of pterygoid; pter. pr - posterior ramus of pterygoid; qj - quadratojugal; smx - septomaxilla; spheth - sphenethmoid; sq. or - otic ramus of squamosal; sq. vr - ventral ramus of squamosal; sq. zr - zygomatic ramus of squamosal.