Odontobatrachus natator (Boulenger, 1905)

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 : 120-124

Taxon classification Animalia Anura Odontobatrachidae

Odontobatrachus natator (Boulenger, 1905)

OTU natator sensu Barej et al. (2015)

Syntypes.

BMNH 1947.2.30.65-69 (syntypes: 1 male, 3 females, subadult), Sierra Leone, no more details available, coll. Major F. Smith.

Examined material.

Sierra Leone: BMNH 1961.1248-54 (5 juveniles), Western Area; BMNH 1963.1047 (female), Southern Province; BMNH 1964.178 (female), Western Area; ZMB 78196 (juvenile), Western Area Peninsula Forest (Latitude: 8.35; Longitude: -13.18), 178 m a.s.l.; ZMB 78197 (female), Western Area Peninsula Forest (8.47; -13.22), 367 m a.s.l.; ZMB 78198 (female), Northern Province (9.21; -11.14), 1325 m a.s.l.; ZMB 78199 (female), Eastern Province (8.86; -10.79), 748 m a.s.l.; ZMB 78200 (male), Northern Province (9.21; -11.14), 1345 m a.s.l.; ZMB 78202, ZFMK 95469 (2 females), ZMB 78203, MHNG 2731.51, ZFMK 95470 (3 males), Eastern Province (7.66; -10.90), 334 m a.s.l. Guinea: ZMB 78207 (juvenile), ZMB 78208 (female), N’Zérékoré Region (8.89; -8.31), 1019 m a.s.l.; ZMB 78209 (female), Kankan Region (9.28; -9.11), 637 m a.s.l.; ZMB 78210 (juvenile), ZMB 78211 (female), N’Zérékoré Region (7.54; -8.84), 403 m a.s.l.; ZMB 78212 (female), ZMB 78213 (male), N’Zérékoré Region (8.88; -8.29), 939 m a.s.l.; ZMB 78214 (male), ZMB 78215-6 (2 females), N’Zérékoré Region (7.64; -9.25), 533 m a.s.l.; ZMB 78217-19 (3 males) Mamou Region (10.30; -11.94), 527 m a.s.l.; ZMB 78303 (female), N’Zérékoré Region (8.35; -9.42), 487 m a.s.l. Liberia: BMNH 1982.631 (male), Iti Valley; ZMB 78220 (female), Grand Cape Mount County (7.45; -10.69), 299 m a.s.l.; ZMB 78221 (female), ZMB 78222 (male), Nimba County (7.54; -8.63), 595 m a.s.l.; ZMB 78223-24, ZMB 78232, ZMB 78234, ZMB 78236-7, ZMB 78239 (7 females), ZMB 78227, ZMB 78229-31, ZMB 78233, ZMB 78235, ZMB 78238, ZMB 78240-42 (10 males), ZMB 78228 (juvenile), Nimba County (7.44; -8.66), 634 m a.s.l.; ZMB 78225 (female), Nimba County (7.44; -8.59); ZMB 78226 (female), Nimba County (7.46; -8.67), 591 m a.s.l.; ZMB 78244 (female), ZMB 78245 (male), Grand Gedeh County (5.66; -8.16), 316 m a.s.l.; ZMB 78246 (juvenile) Grand Gedeh County (5.69; -8.21), 247 m a.s.l.; ZMB 78247 (male), Grand Gedeh County (5.64; -8.19), 367 m a.s.l.; ZMB 78248 (juvenile), Grand Gedeh County (5.64; -8.19), 345 m a.s.l.; ZMB 78249 (female), ZMB 78250 (female, juvenile), Grand Gedeh County (5.63; -8.19), 388 m a.s.l.; ZMB 80504 (male), Nimba County (7.51; -8.70), 429 m a.s.l.; ZMB 80505 (female), Nimba County (6.44; -9.06), 533 m a.s.l.

Boulenger’s (1905) species description is based on a series of five specimens in the BMNH collection (1947.2.30.65-69, formerly: 1905.1.27.4-5 and 1905.2.2.15-17). The type series collected by Major F. Smith Royal Army Medical Corps (R.A.M.C.) contains one male, three females and a subadult female. The type locality is given as "Sierra Leone".

During his service in western Africa, Captain (Local Major) F. Smith researched tropical diseases, prepared species lists of pests and elaborated respective preventive measures ( Smith 1902, 1905). A part of his contribution contains the local fauna around barracks ( Smith 1905) and Major F. Smith mentioned "a local frog (a new species named Petropedetes natator ) …”. He was based in Freetown predominantly surveying the area of Mt. Aureol, Tower Hill and Kortright but likewise carried out short travels to Port Lokkoh (today: Port Loko) and Rotifunk in the close hinterland ( Smith 1902). However, Smith (1902) searched in the latter region for swampy areas as potential breeding habitats of the mosquito genus Anopheles , a habitat type inappropriate for torrent-frogs. Consequently, we herein restrict the type locality of Petropedetes natator Boulenger, 1905 to the Freetown area, Sierra Leone. A more detailed restriction appears unreasonable.

We refrain from designating a single lectotype as subsequent species descriptions are possible with comparison to the whole syntype series.

Genetics.

Odontobatrachus natator 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 natator and other Odontobatrachus species range from 3.40-5.40% (Appendix 1: Table A), while maximum intrataxon differences of Odontobatrachus natator reach 1.98% (one-to-one pairwise comparisons N = 703), maximum intra-subclade difference values for the two subclades of Odontobatrachus natator are 0% (N = 1) and 0.72% (N = 630) respectively (Appendix 1: Table A). These two subclades correspond to the disjunct distribution of I) the Freetown area and II) all remaining localities further inland; divided by unsuitable habitat in-between ( Barej et al. 2015). In case taxonomic changes are made in the future, the Freetown clade should retain the nominate form following the restriction of the type locality.

Description of male syntype.

The male syntype (BMNH 1947.2.30.68) has been assigned to this taxon in both DCA analyses (absolute values and ratios). The male syntype has a robust body shape: snout-urostyle length of 46.1 mm; head width 17.0 mm; head slightly longer than broad; snout in lateral view short, slightly rounded at the snout tip (Fig. 3); snout in dorsal view fairly rounded; lower jaw with sharp tusk-like prolongations and single small knob at lower jaw symphysis with 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 6.4 mm; interorbital distance 5.3 mm; pupil horizontally elliptical; eye diameter distinctly larger than tympanum diameter (Fig. 3); tympanum indistinct (horizontal diameter 2.7 mm); nares closer to snout than to eye; snout as long as eye diameter; canthus rostralis rounded; loreal region concave; paired lateral vocal sacs (Fig. 3); forelimbs moderately slender, forearms slightly hypertrophied, fingers slender; prepollex absent; relative finger lengths III>IV≥II>I (Fig. 3); velvety nuptial excrescences on finger I weakly developed; subarticular tubercles large, subconical; supernumerary tubercles absent; fingertips dilated, triangular, notched in the middle; femur length 23.2 mm; tibia length 23.8 mm; femoral glands large (length × width: left: 10.3 × 5.4 mm, right: 9.5 × 5.5 mm); femoral glands positioned on the posterior part of the ventral side of femur (Fig. 3); relation femoral gland length to femur length: 0.43; minuscule circular glands running along upper side of tibia; foot length (incl. longest toe) 29.9 mm; relative toe lengths IV>III≥V>II>I; inner metatarsal tubercle elliptical; toe tips broadened forming triangular dilated discs; inner metatarsal tubercle prominent (2.8 mm); number of subconical subarticular tubercles on toes I-V: 1, 1, 2, 3, 2; supernumerary tubercles absent (Fig. 3); prominent skin fold on posterior side of feet; dorsal skin texture heterogeneous; dorsum and flanks covered with slender dorsal ridges of app. 3.0 mm length (partially flattened on the dorsum due to preservation); venter smooth; flank texture as on dorsum; webbing fully developed (0-0.5/0-1/0-1/1-0), running as a skin fold along toes III and IV to the disc, webbing between toes hardly concave, almost straight.

Colouration in preservation.

Specimen overall brownish in colour (Fig. 3); dorsum darker than ventrum; throat darker than belly, ventrum lacking any marbling or patterns. Damage of the male syntype: third toe of left foot (in dorsal view) cut off (Fig. 3); left side (in dorsal view) with cut along flank; transverse cut on throat; discs on toes and fingers partially shrivelled due to drying-out.

Variation.

Females are significantly larger than males (SUL: Z = -3.814, p <0.001, Nmales = 22, Nfemales = 29), mean SUL in females 53.6 mm and 48.0 mm in males, and consequently possess longer extremities (FM: Z = -4.395, p <0.001; TI: Z = -4.746, p <0.001; FL: Z = -4.623, p <0.001), broader heads (HW: Z = -3.570, p <0.001) and longer snouts (EN: Z = -2.533, p <0.01; ES: Z = -3.285, p <0.05) in absolute measurements (Tables 1 and 2). However, ratios are predominantly similar between the two sexes, with males only showing higher values in HW/SUL (Z = -2.796, p <0.01), IT/FL (Z = -1.978, p <0.05) and TD/SUL (Z = -2.701, p <0.01); for details see Tables 1 and 2. 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. Variation in webbing formulae of examined specimens in the covered distribution range corresponds to the extent in the type series (Table 7); although skin folds running along toes in the male syntype are more distinct than in many other specimens, showing an almost fully extended webbing state. Dorsal ridges form either slender lines as in the male syntype (Fig. 3, see also Fig. 4b, c) or are short and knob like (Fig. 4a). Number of distinct dorsal ridges (counted from spine to flank) range between two and six, usually three to five ridges per body site. However, both characters were not recognisable due to preservation artefacts in many specimens. Glandular ridges on tibia are usually built of small to large conic glands and form more or less interrupted lines (Fig. 4 a–e). Dorsal colouration (in life) varies from uniform brownish, to mottled patterns with greenish or light brownish background and darker spots, usually arranged along dorsum. Male femoral glands are rose-coloured but colouration may be attenuated by the ventral colouration (Fig. 4e). Belly colouration (in alcohol) ranges from completely pale, dirty whitish, dark throat and pale belly, dark with few pale markings, to entirely dark colouration, showing no sex-dependant colour differentiation.

Distribution.

Odontobatrachus natator has the widest distribution of all congeners (Fig. 1). The species is known from Sierra Leone, Liberia and Guinea. While the species distribution overlaps with Odontobatrachus ziama and Odontobatrachus arndti in eastern Guinea, westernmost localities reach extensions of the Fouta Djallon area, close to the range of Odontobatrachus fouta . Two distinct molecular clades have been uncovered in Odontobatrachus natator ( Barej et al. 2015), one of them being restricted to the Freetown Peninsula in coastal Sierra Leone (FP sensu Barej et al. 2015) and the other covering all remaining localities (IL sensu Barej et al. 2015) of this taxon.

Conservation status.

The EOO, combining both subclades of Odontobatrachus natator ( Barej et al. 2015; therein natator ) sums up to 180,231 km2, resulting in the IUCN Red List category "Least Concern (LC)". However, due to the habitat requirements of this family the AOO is restricted to 224 km2 and thus classifies the species as "Endangered (EN)". When considering the genetic subdivision of Odontobatrachus natator (see Barej et al. 2015), the distribution areas further diminish dramatically, especially for the Freetown Peninsula subclade. While IUCN categories remain constant for the widely distributed subclade, the Freetown Peninsula subclade possesses an AOO of only 20 km2 classifying it as EN and an EOO of 34 km2 placing it as "Critically Endangered (CR)" if treated as its own taxonomic unit.