Odontobatrachus arndti Barej, Schmitz, Penner, Doumbia, Sandberger-Loua, Emmrich, Adeba & Roedel

Barej, Michael F., Schmitz, Andreas, Penner, Johannes, Doumbia, Joseph, Sandberger-Loua, Laura, Hirschfeld, Mareike, Brede, Christian, Emmrich, Mike, Kouame, N'Goran Germain, Hillers, Annika, Gonwouo, Nono L., Nopper, Joachim, Adeba, Patrick Joel, Bangoura, Mohamed A., Gage, Ceri, Anderson, Gail & Roedel, Mark-Oliver, 2015, Life in the spray zone - overlooked diversity in West African torrent-frogs (Anura, Odontobatrachidae, Odontobatrachus), Zoosystematics and Evolution 91 (2), pp. 115-149 : 134-138

Taxon classification Animalia Anura Odontobatrachidae

Odontobatrachus arndti Barej, Schmitz, Penner, Doumbia, Sandberger-Loua, Emmrich, Adeba & Roedel sp. n.

Odontobatrachus arndti OTU4 sensu Barej et al. (2015)

Holotype.

ZMB 78355 (male), Republic of Guinea, Nimba Mts., River Mandey (Latitude: 7.64786; Longitude: -8.42397), 694 m a.s.l., 18 June 2009, coll. L. Sandberger-Loua and J. Doumbia.

Paratypes.

Guinea: MHNG 2731.49 (male), ZMB 78356 (female), N’Zérékoré Region (7.65; -8.42), 670 m a.s.l., 18 June 2009; MHNG 2731.50, ZMB 78357 (2 females), N’Zérékoré Region (7.63; -8.41), 1121 m a.s.l., 4 November 2011; ZFMK 95467 (female), ZFMK 95468 (male), N’Zérékoré Region (7.65; -8.42), 674 m a.s.l., 2 January 2011; ZMB 78354 (female), same data as holotype.

Additional material.

Côte d’Ivoire: ZMB 78326, ZMB 78329 (3 females), ZMB 78327-8 (2 males), Dix-Huit Montagnes Region (7.85; -7.39), app. 500 m a.s.l. Liberia: ZMB 78332 (male), Nimba County (7.56; -8.64), 647 m a.s.l.; ZMB 78333-35 (3 males), Nimba County (7.48; -8.58), 513 m a.s.l. Guinea: ZMB 78336 (female), ZMB 78337-39 (3 males), N’Zérékoré Region (7.61; -8.27), 400 m a.s.l.; ZMB 78340-41 (2 females), N’Zérékoré Region (7.61; -8.26), 460 m a.s.l.; ZMB 78342 (juvenile), N’Zérékoré Region (7.70; -8.40), 751 m a.s.l.; ZMB 78343, ZMB 78345 (2 females), ZMB 78344, ZMB 78346 (2 males), N’Zérékoré Region (7.70; -8.40), 760 m a.s.l.; ZMB 78347 (male), N’Zérékoré Region (7.71; -8.41), 518 m a.s.l.; ZMB 78348 (male), ZMB 78349 (female), N’Zérékoré Region (7.70; -8.40), 764 m a.s.l.; ZMB 78350-1 (2 females), ZMB 78352 (male), N’Zérékoré Region (7.68; -8.39), 1027 m a.s.l.; ZMB 78353 (juvenile), N’Zérékoré Region (7.65; -8.42), 670 m a.s.l.; ZMB 78358-59 (2 males), N’Zérékoré Region (7.65; -8.34), 577 m a.s.l.; ZMB 78360 (female), ZMB 78361 (male), N’Zérékoré Region (7.65; -8.36), 815 m a.s.l.; ZMB 78362 (female), ZMB 78363 (male), N’Zérékoré Region (7.63; -8.35), 652 m a.s.l.; ZMB 78364, ZMB 78367 (2 females), ZMB 78365-6 (2 males), N’Zérékoré Region (7.65; -8.37), 949 m a.s.l.; ZMB 78368 (female), ZMB 78369 (male), N’Zérékoré Region (7.67; -8.37), 1317 m a.s.l.; ZMB 78370 (male), ZMB 78371 (female), N’Zérékoré Region (7.67; -8.37), 1234 m a.s.l.; ZMB 78372 (female), ZMB 78373 (male), N’Zérékoré Region (7.62; -8.42), 1154 m a.s.l.; ZMB 78374 (female), ZMB 78375 (male), N’Zérékoré Region (7.62; -8.45), 701 m a.s.l.; ZMB 78376 (female), ZMB 78377 (male), N’Zérékoré Region (7.63; -8.44), 750 m a.s.l.; ZMB 78378 (female), ZMB 78379 (male), N’Zérékoré Region (7.67; -8.35), 786 m a.s.l.; ZMB 78380 (female), ZMB 78381 (male), N’Zérékoré Region (7.67; -8.40), 998 m a.s.l.

Diagnosis.

Medium to large sized frogs, robust body shape; head narrow, highest eye diameter/eye-naris-distance ratio in the family, low mean tympanum diameter orbita diameter ratio, webbing almost fully developed, leaving 0.25-0.5 of the distal phalange free at the inner side of toe II, leaving 0.75-1 of the distal phalange free at toe IV, belly pattern very variable, glandular lines on tibia contain mean conic glands forming frequently interrupted lines. Genetically Odontobatrachus arndti differs by a minimum of 2.89% in the mitochondrial 16S gene from its congeners.

Differential diagnosis.

Odontobatrachus arndti can be distinguished from its congeners by a combination of characters (characters distinguishing Odontobatrachus arndti vs. Odontobatrachus ziama , Odontobatrachus smithi and Odontobatrachus fouta see above; for all significant differences see Table 5): male Odontobatrachus arndti differ from Odontobatrachus natator by the following ratios (Table 1): larger TI/SUL, FL/SUL, O/EN and smaller HW/SUL, TD/O, IT/FL, TD/SUL in Odontobatrachus arndti than in Odontobatrachus natator ; female Odontobatrachus arndti differ from Odontobatrachus natator by the following ratios (Table 2): smaller FM/TI, HW/SUL and O/EN larger in Odontobatrachus arndti than in Odontobatrachus natator . Webbing formulae are very similar in the two species (Table 7). Glandular lines on tibia contain small to mean conic glands forming hardly interrupted lines in Odontobatrachus arndti (Fig. 12b, c), while similar to Odontobatrachus fouta small to large glands form more or less interrupted lines in Odontobatrachus natator (Fig. 4 a–e).

Genetics.

The species is genetically well differentiated from all congeners and known populations form a well-supported and monophyletic clade ( Barej et al. 2015). Uncorrected 16S p-distances between Odontobatrachus arndti and other Odontobatrachus species range from 2.89-5.55%, while maximum intrataxon differences of Odontobatrachus arndti add up to 0.58% (mean value 0.05%; N = 861; Appendix 1: Table A).

Holotype description.

The male holotype has been assigned to this taxon in both DCA analyses (absolute values and ratios). The holotype is an adult male with a slightly robust body (Fig. 11): snout-urostyle length of 48.8 mm; head width 17.1 mm; head slightly longer than broad; snout in lateral view short, flattened and rounded at the snout tip; snout in dorsal view triangular, rounded; lower jaw with sharp tusk-like prolonga tions protruding the skin and single triangular knob at lower jaw symphysis, corresponding socket in between premaxillae; upper premaxillae and maxillae with numerous teeth, posteriorly curved; vomerine teeth present, arranged in two small odontophores, closer to each other than to choanae; tongue broadly heart shaped; horizontal eye diameter 7.6 mm; interorbital distance 5.2 mm; pupil horizontally elliptical; eye diameter distinctly larger than tympanum diameter; tympanum distinct (horizontal diameter 2.7 mm); nares closer to snout than to eye; snout shorter than eye diameter; canthus rostralis rounded; loreal region concave; paired lateral vocal sacs; forelimbs robust, forearms hypertrophied, fingers slender; prepollex absent; relative finger lengths III>IV>II>I; velvety nuptial excrescences weakly developed on finger I; subarticular tubercles large, subconical; supernumerary tubercles absent; fingertips dilated, triangular, notched in the middle; femur length 24.6 mm; tibia length 26.3 mm; femoral glands large (length × width: left: 12.9 × 8.0 mm, right: 13.1 × 7.8 mm); femoral glands positioned on the posterior part of the ventral side of femur; relation femoral gland length to femur length: 0.53; minuscule circular glands running along upper side of tibia; foot length (incl. longest toe) 34.9 mm; relative toe lengths IV>III>V>II>I; shortest toe 6.4 mm; inner metatarsal tubercle elliptical; toe tips broadened forming triangular dilated discs; inner metatarsal tubercle prominent (3.8 mm); number of subconical subarticular tubercles on toes I-V: 1, 1, 2, 3, 2; supernumerary tubercles absent; prominent skin fold on posterior side of feet; dorsal skin texture heterogeneous; dorsum and flanks covered with slender dorsal ridges of app. 2.5-3.5 mm (partially flattened); venter with fine granulation; flank texture rough and granular as dorsum; webbing fully developed (0-0/0-1/0-0.75/0.75-0); webbing between toes hardly concave. Damage of the male holotype: cut at pectoral region (liver tissue sampled) and skin cut on right lumbar region (in ventral view); glandular dorsal ridges partially not recognisable due to preservation.

Colouration of holotype in alcohol

(Fig. 11). Dorsum dark brownish, few paler marblings; hind limbs coloured as dorsum; throat pale with few darker marblings; venter pale, area around incision darker; pale colouration between axillaries and elbows, femoral glands pale, clearly silhouetted from femora, with blurred minuscule reticulation; femora and tibia pale as belly.

Variation.

Females are significantly larger than males (SUL: Z = -4.933, p <0.001, Nmales = 26, Nfemales = 24), max SUL in females 64.0 mm and 53.6 mm in males, and consequently possess longer extremities (FM: Z = -3.894, p <0.001; TI: Z = -4.458, p <0.001; FL: Z = -4.264, p <0.001), broader heads (HW: Z = -4.090, p <0.001), longer snouts (EN: Z = -2.678, p <0.01; ES: Z = -2.906, p <0.01) and larger eyes (Z = -2.779, p <0.01), larger TD (Z = -2.214, p <0.05). However, ratios are predominantly similar between the two sexes, although males show higher values in FL/SUL (Z = -2.214, p <0.05), FM/SUL (Z = -2.932, p <0.01), FM/TI (Z = -3.010, p <0.01) and HW/SUL (Z = -4.136, p <0.001). Both sexes possess enlarged tusk-like prolongations in the lower jaw as well as the name-bearing ‘teeth’ on the upper jaw. Male secondary sexual characters are femoral glands, velvety nuptial excrescences on finger I and presence of vocal sacs. Webbing formulae showed little variance (Table 7). However, some specimen possess a more extensive webbing on toe IV (0.5/0.5). Dorsal ridges are elongated and slender (Fig. 12 a–c). Number of distinct dorsal ridges (counted from spine to flank) ranges between three and six, usually four to five ridges per body site. Glandular ridges on tibia usually are built of small to mean conic glands and form hardly interrupted lines (Fig. 12b, c). However, both characters were not recognisable due to preservation artefacts in many specimens. Dorsal colouration (in life) varies from almost black, beige with reddish-brown spots ar ranged in longitudinal lines (Fig. 12; Guibé and Lamotte 1958; Rödel and Bangoura 2004). Male femoral glands are yellow ( Rödel 2003). Belly colouration (in alcohol) is very variable, ranging from completely whitish, dirty whitish, a distinct reticulation pattern, dark throat with marbling on belly, marbling on throat and belly blurring to paler colouration posteriorly, to completely dark throat and belly, showing no sex-dependant differentiation.

Acoustics.

Three calls of Odontobatrachus arndti were recorded from specimens in terraria. Calls sound like a repeat of “chucks”, consisting of several tonal notes. Two harmonics were visible (Fig. 13), the second harmonic being the dominant frequency (2842.4-3359.2 Hz), the first being the fundamental frequency (1421.2-1679.6 Hz). The call duration ranged from 1.2 to 3.0 s. One call comprised 22 notes (Fig. 13a) and the other two comprised five notes each (Fig. 13b). Each note had a duration of 34.7 ± 0.01 ms (N = 32). The notes were separated from each other by pauses of 238.0 ± 0.01 ms (N = 12) with the two calls comprising five notes (Fig. 13b). Pause duration in the third call (22 notes) was decreasing from 160.0 to 67.0 ms from the beginning towards the end of the call (Fig. 13a). Rödel’s (2003) anecdotal report of a torrent frog call from Mt. Sangbé ( Côte d’Ivoire) comprising a series of click sounds with ever-shorter intervals corresponds to the second call type (22 notes).

Distribution.

Odontobatrachus arndti is known to occur on the Nimba Mts. in Guinea and Liberia, the adjacent areas at Mt. Gangra (Liberia) and Déré (Guinea), as well as the Mt. Sangbé in western Côte d’Ivoire (Fig. 1). This taxon represents the easternmost representative of the family. Localities at the southern end of the Nimba Mts. and along Mt. Gangra are in very close proximity to Odontobatrachus natator . Both species inhabit similar altitudes at the foot of the Nimba Mts. However, at present no differing habitat requirements or ecological adaptations are known ( Barej et al. 2015), which could explain their spatial separation.

Etymology.

The species epithet arndti was chosen in order to honour Prof. emerit. Dr. Rudolf G. Arndt, New Jersey USA, for his trust in young academics and his invaluable support of this study.

Common name.

We advise to use the term ‘‘Arndt’s torrent-frog’’ in English and ‘‘ grenouilles des torrents d’Arndt” in French.

Conservation status.

Both, the EOO of 2595 km2 and the AOO of 156 km2 classify Odontobatrachus arndti as "Endangered (EN)" ( Barej et al. 2015).