A tiny new species of Platypelis from the Marojejy National Park in northeastern Madagascar (Amphibia: Microhylidae)

We describe a tiny new frog species of the genus Platypelis (Anura: Microhylidae: Cophylinae) from Marojejy National Park, northeastern Madagascar. Platypelis ravus sp. nov. differs from all other known Platypelis and Cophyla species by its small size (17-19 mm snout-vent length) and a combination of other morphological and bioacoustic characters. The new species seems to be most closely related to P. milloti with which it shares the principal colour pattern, but exhibits a yellow rather than red posterior venter. Uncorrected pairwise sequence divergence in a 16S rRNA gene fragment to all other known species of the genus (except P. cowanii for which no genetic data is available) is greater than 6%. We suggest the inclusion of the new species in the IUCN threat category “Data Defi cient”.

Arboreal cophylines include the genera Anodonthyla, Cophyla, Platypelis and a few species of the genus Plethodontohyla. Anodonthyla is relatively well characterized by the presence of a distinct prepollex in males and the absence of vomerine teeth. The distinction of Cophyla and Platypelis is less clear and mainly based on osteological characters (Blommers-Schlösser & Blanc 1991). Cophyla is the sister group of Platypelis based on molecular data (Wollenberg et al. 2008).
During fi eldwork in 2005, we collected specimens of a Platypelis from the Marojejy National Park in northeastern Madagascar that distinctly differ from all cophylines known so far. We describe this new species in the following.

Material and Methods
Specimens were collected at night by opportunistic searching and localizing calling males, using torches and head lamps. They were euthanized in a chlorobutanol solution, fi xed in 95% ethanol and preserved in 70% ethanol. Locality information was recorded with GPS receivers. Type specimens of the new species are deposited in the Zoologische Staatssammlung München (ZSM) and the Université d'Antananarivo, Département de Biologie Animale, Madagascar (UADBA). FGZC refers to F. Glaw fi eld numbers. Terminology for biogeographic regions of Madagascar follows Glaw & Vences (2007).
Calls were recorded in the fi eld using a Sony WM-D6C tape recorder and external microphones (Sennheiser Me-80, Vivanco EM 238). Recordings were sampled at 22.05 kHz and 16-bit resolution and computer-analysed using the software Adobe Audition. Frequency information was obtained through Fast Fourier Transformation (FFT; width 1024 points). The spectrogram was obtained at Hanning window function with 256 bands resolution. Temporal measurements are given as range, with mean ± standard deviation in parentheses. Terminology in call description follows Vences et al. (2010).
Molecular genetic analyses were conducted by Wollenberg et al. (2008) and Vieites et al. (2009). See those studies for exact methodology applied.

Etymology
The specifi c epithet is an adjective derived from Latin ravus = grayish-yellow, referring to the diagnostic ventral colour of the species.

Diagnosis
The new species is assigned to the genus Platypelis based on enlarged terminal fi nger discs, absence of prepollex, and molecular phylogenetic relationships (Wollenberg et al. 2008). It differs from other arboreal cophyline microhylids of the genus Anodonthyla by the absence of a prepollex in males, and from Plethodontohyla with enlarged fi nger and toe discs [P. guentheri Glaw & Vences, 2007 Andreone, Fenolio & Walvoord, 2003, P. milloti Guibé, 1950, P. pollicaris Boulenger, 1888, P. tsaratananaensis Guibé, 1974, and P. tuberifera (Methuen, 1920 by distinctly smaller size (SVL of adult males 17-19 mm vs. 23-88 mm), and from P. tetra Andreone, Fenolio & Walvoord, 2003 by presence of a regular pattern of moderately-sized tubercles on the back (vs. four symmetrically arranged and distinctly enlarged white tubercles), a third toe of the same length than the fi fth (vs. toe three longer than toe fi ve), by presence of yellow ventral colouration (vs. absence), and by a much higher note repetition rate of the advertisement calls. It differs from Cophyla occultans (Glaw & Vences, 1992) by smaller size (SVL 17-19 mm vs. 18-21 mm), and equal length of toe 3 and 5 (vs. toe 3 < 5). It is distinguished from Platypelis barbouri Noble, 1940 (and most likely from its junior synonym Paracophyla tuberculata Millot & Guibé, 1951, described from the well sampled type locality Andasibe) by absence of red colour on the ventral side of the hindlimbs and belly, and a largely smooth dorsal surface (vs. strongly tuberculate).
Summarizing, the new species is most similar to P. barbouri (the only other Platypelis without vomerine teeth and in addition with a rather similar advertisement call, but with reddish instead of yellow ventral surface, and more strongly expressed and irregularly arranged tubercles on dorsal surface), and to P. mavomavo (with yellow ventral surface but distinctly larger SVL). It differs, however, from these and all other nominal species of Platypelis and Cophyla (except P. cowanii fo r which no genetic data is available) by a high genetic divergence (see Wollenberg et al. 2008;Vieites et al. 2009 and unpublished data for P. alticola, P. tsaratananaensis, P. tetra and Cophyla occultans). Phylogenetically, it appears to be sister to P. milloti (see below) which however is larger, has a much more contrasting dorsal pattern, red colour ventrally, and a much faster note repetition rate in advertisement calls (106/min vs. 18-19/ min).

Description of the holotype
Specimen in good state of preservation, some muscle tissue removed from right thigh, snout-vent length 19.1 mm. Body slender; head as wide as long, not wider than body; snout bluntly rounded in dorsal and lateral views; nostrils directed dorsolaterally, not protuberant, nearer to tip of snout than to eye; canthus rostralis indistinct, very slightly concave; loreal region plain; tympanum moderately distinct, 56% of eye diameter; supratympanic fold moderately distinct, straight; tongue ovoid, not bifi d or notched; weakly expressed maxillary teeth present; vomerine teeth absent; choanae rounded. Forelimbs slender; subarticular tubercles single, fl at, and hardly recognizable; outer metacarpal tubercle probably large and fl at, but very diffi cult to recognize; inner metacarpal tubercle large, forming distinct protuberance at base of fi rst fi nger; hand with traces of webbing only between fi ngers 3 and 4; fi ngers distinctly fl attened and relatively broad along entire length; relative length of fi ngers 1 < 2 < 4 < 3, fourth fi nger distinctly longer than second; fi nger discs distinctly enlarged, slightly triangular; nuptial pads absent. Hindlimbs slender; tibiotarsal articulation reaching tympanum when hindlimb adpressed along body; tibia length, 39% of SVL; lateral metatarsalia strongly connected; inner metatarsal tubercle small and fl at, diffi cult to recognize; outer metatarsal tubercle absent; webbing between toes weakly developed, with traces of web between second and third toe, and some webbing between third and fouth, and fourth and fi fth toe; webbing formula diffi cult to assess because subarticular tubercles on toes are hardly recognizable; toes fl attened and relatively broad along their entire length; relative length of toes 1 < 2 < 3 = 5 < 4; third toe of similar length as fi fth. Dorsal skin smooth, without dorsolateral folds. Ventral skin slightly granular on throat, smooth on chest and moderately granular on belly.
After fi ve years in 70% ethanol, dorsum light brown with distinct and well-delimited symmetrical dark brown markings: a heart-shaped marking starting between eyes and extending on posterior head, bordered anteriorly by a light brown band between eyes; a W-shaped marking on anterior dorsum; and a chevron-shaped marking on posterior dorsum. Shank and foot with one distinct dark crossband each, another dark crossband on anterior hand. Ventrally, the throat is dark brown and this dark colour fades at the level of the chest into a whitish colour on posterior belly. Limbs light with some dark brown pigment.
In life (Fig. 1), two series of regularly arranged and light-coloured small tubercles recognizable on the dorsum, with fi ve and three tubercles bordering the anterior edges of the W-shaped and chevron-shaped dark markings, respectively. In life (Fig. 1A), the colour was very similar to that in preservative but more contrasted. The interorbital band was posteriorly beige. The iris was uniformly bronze. Throat and chest were grayish. The yellow ventral colour extended onto the lateral part of the inguinal region. Also the fi nger and toe discs (especially of fi rst fi nger) were yellowish.

Variation
The two ZSM paratypes are very similar in external morphology and colour pattern when compared to the holotype (Table 1), but have a thin light middorsal line, and (in preservative) ventrally less dark pigment, especially in ZSM 351/2005 which is mostly light coloured ventrally. The UADBA paratypes were not available for detailed studies but were in general similar to the ZSM paratypes.

Natural History
Numerous specimens of the new species were heard in the evening in dense primary forest directly next to Camp Simpona campsite, calling from leaves in bushes and on trees at perch heights of 1-2 m above the ground.

Molecular differentiation
DNA sequences of various mitochondrial genes determined from the holotype of Platypelis ravus were included in a comprehensive molecular analysis of cophyline phylogeny, under the name Platypelis sp. 2 (Wollenberg et al. 2008), and are deposited in GenBank under accession numbers EU341101 (12S and 16S genes) and EU341035 (cytochrome b gene). According to this study, the species is deeply genetically divergent from other Platypelis and was grouped by some analyses as sister species of Platypelis milloti. According to Vieites et al. (2009) the pairwise uncorrected sequence divergence (p-distance) in a fragment of the 16S rRNA gene of P. ravus (as P. sp. 4) to all other cophylines was above 6%.

Discussion
With the description of Platypelis ravus sp. nov. we add a distinctive new species to the genus Platypelis which represents -together with P. tetra (see Andreone et al. 2003) -the smallest species of the Platypelis / Cophyla clade. Phylogenetic analyses (Wollenberg et al. 2008) placed the new species with some confi dence sister to P. milloti. Although at fi rst glance these two species are very distinctive in numerous characters, including size and advertisement calls, it is interesting that they bear some similarities in the dorsal colour pattern. Platypelis milloti has a dorsal pattern of strongly contrasting black blotches of almost the same shape as the poorly contrasting dark blotches in P. ravus sp. nov. (see pictures in Glaw & Vences 2007). Also the light bar between the eyes and the vertebral line typical for P. ravus sp. nov. are seen more strongly expressed in P. milloti. Furthermore, the general ventral pattern is similar, except that the posterior venter is coloured red in P. milloti and yellow in P. ravus sp. nov. It is therefore appealing to hypothesize that this similarity of colour pattern between the two species is due to common ancestry.
Platypelis ravus sp. nov. is so far only known from its type locality. Own surveys in rainforests of other mountain massifs in northern Madagascar at similar elevations (e.g. Montagne d'Ambre, Manongarivo, Tsaratanana, Makira, at elevations of 900-2500 m) have so far failed to yield additional specimens attributable to P. ravus sp. nov., and we therefore cannot exclude that this species is indeed endemic to the Marojejy massif, as it seems to be the case for several other frog species occurring at comparable elevation in this mountain massif (e.g. Gephyromantis tahotra Glaw, Köhler & Vences, 2011, G. tandroka Glaw & Vences, 2001, G. schilfi Glaw & Vences, 2000. In another survey at Marojejy, Raselimanana et al. (2000) identifi ed fi ve species of the Platypelis / Cophyla clade (P. barbouri, P. grandis, P. tsaratananaensis, P. tuberifera and C. occultans) and we cannot exclude that their high altitude records of C. occultans (recorded form 350-1300 m altitude) include P. ravus sp. nov., a similarly tiny species. However, as we are aware of only six specimens from a single locality, we suggest to consider P. ravus sp. nov. 'Data Defi cient' according to the IUCN Red List criteria (IUCN 2001).