Mantidactylus (Brygoomantis) noralottae, Mercurio & Andreone, 2007

Mercurio, Vincenzo & Andreone, Franco, 2007, Two new canyon-dwelling frogs from the arid sandstone Isalo Massif, central-southern Madagascar (Mantellidae, Mantellinae), Zootaxa 1574 (1), pp. 31-47 : 38-43

Mantidactylus (Brygoomantis) noralottae n. sp.

( Fig. 4 )

Diagnosis. A species attributed to the genus Mantidactylus based on the following characters (1) presence of femoral glands of type 3, smaller in females, (2) presence of a single subgular vocal sac, and (3) absence of nuptial pads in males. This species is included in the subgenus Brygoomantis due to genetic and bioacoustics evidence. Further morphological characters are: body medium sized; tympanum of males distinctly larger than those of females; tibiotarsal articulation reaches between eye and nostrils; metatarsalia separated; toes webbed; fingertips moderately enlarged; and males with single, subgular vocal sac. Distinction from other species of Brygoomantis is mainly based on the isolated distribution and molecular relationships of the new species (see below).

Holotype. MRSN A5317 ( FAZC 13023 ), adult male, Ambovo, Parc National de l’Isalo , Fianarantsoa Faritany, Ranohira Fivondronana , 22°30.48’S, 45°21.15’E, 996 m a.s.l, collected by V. Mercurio and T.J. Razafindrabe on 18 December 2004, fixed in 4% formalin.

Paratypes. MRSN A5036 ( FAZC 13021 ) and A5319 ( FAZC 13022 ), adult males; MRSN A5035 ( FAZC 13020 ), A5254 ( FAZC 13008 ) and A5318 ( FAZC 13024 ), adult females; all five specimens with the same locality, date and collectors as the holotype, fixed in 4% formalin; SMF 85861 (ex MRSN A5253 ( FAZC 13007 ), PBZT-FAZC 12998 (not measured), adult males; SMF 85862-64 (ex MRSN A5255-5257 ( FAZC 13011-13013 ), MRSN A5252 ( FAZC 13005 ) and PBZT-FAZC 12996 (not measured), adult females; all seven specimens with the same locality, date and collector as the holotype, fixed in 90° ethanol.

Description of the holotype. Male specimen in good state of preservation. Snout-vent length 35 mm, for other measurements see table 2. Body slender; head longer than wide; snout pointed in dorsal view, rounded in lateral view; nostrils directed laterally, protuberant, nearer to tip of snout than eye; canthus rostralis distinct, straight; tympanum distinct, elliptical, 81.6% of eye diameter; supratympanic fold distinct, regularly curved; tongue ovoid, posteriorly bifid; maxillary and vomerine teeth present; choanae elliptical. Arms slender; fingers without webbing; distinct single subarticular tubercle; finger discs distinctly enlarged, elliptical. Hind limbs slender, tibiotarsal articulation reaches between eye and nostrils; lateral metatarsalia separated; inner metatarsal tubercles distinct, outer absent; webbing between toes: 1(1), 2i(1), 2e(0), 3i(1.5), 3e(0.75), 4i(1), 4e(1), 5(0). Dorsal skin smooth without dorsolateral folds. Ventral skin smooth on throat, chest and belly. Femoral glands of type 3 with presence of the “structure B” very distinct from external view, overall appearance of glands very granular, 7.6 mm length and 4.2 mm width; from internal view left gland elliptical of 2.2 mm length, with 8 granules of 0.7 mm diameter. Dorsal colouration brownish softly spotted especially on the canthal region and behind the eyes. Tympanic area brownish bordered by a darker supratympanic fold. Faint darker crossbands present on arms and limbs. Ventrally whitish spotted with irregular brownish markings especially on throat, chest, hands and feet. Vocal sac single, subgular, and slightly distensible. After one year in preservative the chromatic pattern are the same as in life but with faded colours.

Variation. The paratypes largely agree with the holotype in morphology and colouration. Chromatic differences lie in: a) presence of a lighter vertebral band; b) extension of darker pigmentation on tympanum; and c) extension and pattern of pigmentation on snout. MRSN A5254 presents a more contrasted dorsal colouration with well defined crossbands on limbs, a light vertebral band, a well defined lighter triangular shaped spot on snout extending to anterior part of eyes, and a darker tympanic area. MRSN A5319 is similar in colouration to the holotype but differs in having a more contrasted light triangle on snout. MRSN A5035 and A5252 are also similar to the holotype but they have a darker tympanic area, as well as SMF 85863 and 85864. SMF 85863 lacks the left foot maybe due to predation. Femoral glands are well defined and visible from external view in all the male specimens, reduced in form of small circular gland of about 1.0 mm diameter composed by a single flattened granule in females.

Etymology. V. Mercurio wishes to dedicate the new species to his wife Nora Lotta Fröhder (now Nora Lotta Mercurio) in recognition of her never-ending support and patience.

Natural history. Mantidactylus noralottae is known for the Isalo Massif only. We found several individuals inside a narrow canyon in the initial and gully tracts (Mercurio & Andreone, 2006). Calling males were hanging at night on the almost vertical canyon walls at about 150–200 cm above the bottom or the water surface. Females and males were also found on the canyon bed inside the water pools. As far as known, M. noralottae is the only species ascribed to the subgenus Brygoomantis with such scansorial habits. They are able to climb almost vertical walls. After the dissection of six specimens to check the stomach contents we found 55 prey items divided as follows (number of prey item/percentage of the sampling): Hymenoptera , Formicidae (33, 60.0%); Coleoptera (16, 29.1%); Diptera (3, 5.4%); Aranea (1, 1.8%); Hymenoptera , undetermined (1, 1.8%); and Orthoptera (1, 1.8%).

Advertisement call. Calling male MRSN A5319 recorded at Ambovo, Parc National de l’Isalo (on 18 December 2004, 20:00, 20°C). The call consisted of a single long note (2.6 sec) composed of a train of about 100 short pulses ( Fig. 5 , table 4). The pulse train originates during expiration and is associated with a strong vibration of the body wall. Pulses are poorly toned and harmonics are not clearly visible in the spectrogram. Fundamental frequency is around 1000 Hz while dominant frequency is about 1400 Hz. Frequency ranges from 900 to 3000 Hz. The calls are emitted after rather long time intervals (6 sec).

Morphological comparison with other species. Based on the basis of genetic and bioacoustics evidences Mantidactylus noralottae has been placed in the subgenus Brygoomantis . However, like the other species belonging to this subgenus superficial similarities are shared with the species belonging to subgenus Ochthomantis . Convincing synapomorphies on adult morphology able to clearly cut species belonging to both subgenera are currently unknown ( Glaw & Vences, 2006). In particular, at the Isalo Massif M. noralottae lives in sympatry with M. sp. aff. ulcerosus (Boettger) and in syntopy with M. cf. femoralis (Boulenger) . Adults of M. noralottae can be confused with juveniles of M. cf. femoralis and, at a lesser extent, with adult specimens of M. sp. aff. ulcerosus . Mantidactylus noralottae can be distinguished from M. sp. aff. ulcerosus by: (a) different dorsal colouration (brownish softly spotted vs. uniformly light brown to greyish sometimes with darker patches; (b) dorsal skin (smooth vs. granular); (c) general overall appearance (slender vs. stout); (d) advertisement call (single prolonged note vs. 8–14 notes). It can be distinguished from the other Brygoomantis species by the following combinations of characters: body dimension (smaller in M. alutus (Peracca) , M. biporus (Boulenger) , M. tricinctus (Guibé) , and larger in M. ambohimitombi Boulenger ); by dorsal colouration and presence of vomerine teeth ( M. madecassus Millot & Guibé and M. pauliani Guibé ); by dorsal skin texture and hind limb length (skin granular in both M. betsileanus and M. curtus , hind limbs comparatively longer in the first and shorter in the second); and by different advertisement calls (from the recently resurrected taxa M. bellyi Mocquard and M. bourgati Guibé ). Convincing differences in call parameters between M. noralottae and M. betsileanus are still in need of identification, largely depending on an upcoming taxonomic revision of the subgenus Brygoomantis . Mantidactylus noralottae can be distinguished from the syntopic M. cf. femoralis by: (a) different dorsal colouration (lighter without black stripes and yellow spot on flanks vs. darker with presence of black stripes and yellow spot on flanks), (b) different ventral colouration (slightly marbled on chest, belly dirty without black lines on throat vs. heavily marbled, belly spotted, black lines on throat often present), (c) hind limbs length (tibiotarsal articulation reaches between eyes and nostrils vs. tip of snout or beyond); d) body size (34.1 mm, males, and 37.7 mm, females vs. 37.8 mm, males, and 44.7 mm, females) and, (e) body shape (slender vs. quite stout). Mantidactylus noralottae can be distinguished from the other species belonging to the Ochthomantis subgenus ( M. ambreensis Mocquard , M. majori Boulenger , M. mocquardi Angel and M. zolitschka Glaw & Vences ) by: (a) dorsal colouration uniformly brownish more or less spotted, (b) dorsal skin smooth, (c) smaller body size (male SVL <40 mm vs.> 40 mm except for M. ambreensis ) and (d) comparatively enlarged inner metatarsal tubercle, (e) advertisement call.

Mitochondrial differentiation. Accession numbers of newly obtained sequences: MRSN A5252, EF222306 ; SMF 85861, EF222307 ; MRSN A5254, EF222308 ; SMF 85862, EF222309 ; SMF 85863, EF222310 ; SMF 85863, EF222311 . The uncorrected pairwise DNA divergence of the Mantidactylus noralottae 16S rRNA gene sequence compared to that of M. betsileanus from Mandraka (East Madagascar) is 3.6 %, while the difference with M. ulcerosus from Berara (NW Madagascar) corresponds to 11.5%–11.9% (M. Vences, pers. comm.). This divergence fully supports the specific status of M. noralottae .

Conservation. Mantidactylus noralottae , similarly to Gephyromantis azzurrae , appears to be a localized species occurring only in the northern part of the Isalo Massif. Taken into consideration that it is known from a single locality within the Parc National de l’Isalo we cannot say too much about the impending threats. However, we preliminarily classify M. noralottae as Critically Endangered, following the geographic criteria, B2ab(iii). As for G. azzurrae we consider that this categorisation could be changed if some other localities (outside the Isalo massif) will be discovered in the future.

Available names. According to Blommers-Schlösser & Blanc (1991), several available names in the subgenus Brygoomantis are to be considered as junior synonyms of valid species or dubious names. Mantidactylus noralottae differs genetically from all sequenced Brygoomantis species belonging to the M. betsileanus group (M. Vences, pers. comm.), thus representing a likely vicariant western species. Taxa known from western localities (potentially conspecific with M. noralottae ) are Rhacophorus fumigatus Mocquard (type locality “ Madagascar côte ouest”) and Mantidactylus brunneus Ahl (type locality "Nord-West-Madagascar") both currently considered as synonyms of M. betsileanus , and Mantidactylus tripunctatus Angel (type localities " Pic St. Louis, province de Fort-Dauphin " and "Befotaka, province de Farafangana ”), considered as nomen dubium ( Glaw & Vences, 1994; 1999). According to the original description of the holotype of M. tripunctatus the finger discs are very small and smaller than those of toes; the tibiotarsal articulation reaches the tip of snout or between tip of snout and eyes; SVL of largest syntype is 30 mm. M. noralottae can be unequivocally distinguished from M. tripunctatus by the combination of comparatively larger finger discs, shorter hind limbs, and larger body size.

Figures

FIGURE 4. Mantidactylus noralottae n.sp. in life: A) dorso-lateral and B) ventral view of the paratype MRSN A5319 (male) from Ambovo, Isalo Massif.

FIGURE 5. Sonagram (above) and oscillogram (below) of the advertisement calls of Mantidactylus noralottae n.sp. from Ambovo, Isalo Massif.