Blommersia nataliae, Vieites & Nieto-Román & Fernández & Santos-Santos, 2020

Vieites, David R., Nieto-Roman, Sandra, Fernandez, Marcos Peso & Santos-Santos, Javier H., 2020, Hidden in plain sight: a new frog species of the genus Blommersia from the oceanic island of Mayotte, Comoros archipelago, ZooKeys 994, pp. 149-166 : 149

Blommersia nataliae sp. nov.

Holotype.

An adult male, left thigh muscle removed for genetic analyses. Original field number: "DRV6867, David R. Vieites collection". Museo Nacional de Ciencias Naturales catalog number: MNCN50456. Collected in a degraded forest with giant bamboo, in forest leaf litter at the Mont M’Sapere, island of Mayotte (French Overseas Department), Comoros archipelago, - 12.7656°S, 45.1852°E 500 m a.s.l. the 25th November 2012 by D. Vieites and M. Peso Fernández.

Paratypes.

Females DRV6808 (MNCN50451), DRV6854 (MNCN50447), DRV6855 (MNCN50448), DRV6868 (MNCN50450), DRV6869 (MNCN50449); males DRV6857 (MNCN50453), DRV6859 (MNCN50455), DRV6860 (MNCN50458), DRV6861 (MNCN50454), DRV6862 (MNCN50452), DRV6863 (MNCN50457), collected at the type locality at the Mont M’Sapere in 2012 by D. Vieites and M. Peso Fernández.

Etymology.

Noun in the genitive case. D. Vieites and S. Nieto dedicate this species to their daughter Natalia Vieites Nieto, who has a birthmark resembling the beautiful conspicuous round moon-like brown spot characteristic of the species.

Diagnosis.

Assigned to the genus Blommersia in the family Mantellidae and subfamily Mantellinae by a combination of (1) presence of femoral glands and absence of nuptial pads in males, (2) presence of intercalary elements between ultimate and penultimate phalanges of fingers and toes (verified by external examination and microCT scanning), (3) presence of a single subgular vocal sac in males, (4) small size (adult SVL <30 mm), and (5) molecular data.

Within the genus Blommersia , B. nataliae sp. nov. is characterized by the following unique suite of morphological characters: (1) small adult body size (SVL 18-23 mm), (2) round femoral glands that are distantly separated in males, (3) inconspicuous vomerine teeth, (4) ovoid tongue, (5) tibiotarsal articulation reaching between the eye and the nostril when adpressed along the body. Furthermore, the new species is differentiated from all other species of Blommersia by a significant molecular genetic differentiation (≥ 4.3% uncorrected pairwise-distance in 16S).

Blommersia nataliae sp. nov. can be distinguished from all other described Blommersia species except B. wittei and B. transmarina by the presence of vomerine teeth (vs. absence) and having separated metatarsalia (vs. unseparated).

Blommersia nataliae sp. nov. can be distinguished from its syntopic sister taxon B. transmarina by its rounded, distantly separated femoral glands (versus oblong, less separated glands; Figs 2 - 3 ). Fig. 4 represents the relative femoral gland length versus the relative distance between the femoral glands’ inner edges for both species and their sister taxon from Madagascar, B. wittei . B. wittei has an intermediate position between B. nataliae sp. nov. and B. transmarina ; where B. nataliae sp. nov. presents rounded and shorter glands that are ca. two times more separated between each other than in B. transmarina (median FGD 2.6 ± 0.2 mm vs. 1.3 ± 0.3 mm, respectively) and ca. half shorter (median FGL 2.6 ± 0.4 mm vs. 4.8 ± 0.5 mm) (see also Figs 2 - 3 ). Blommersia nataliae sp. nov. also differs from B. transmarina in having inconspicuous vomerine teeth versus well developed and showing a V shape, ovoid tongue (vs. bifid), shorter hindlimbs with tibiotarsal articulation reaching between the eye and the nostril (vs. surpassing well the snout when appressed along the body), less distinct inner metatarsal tubercle, webbing formula [1(1), 2i(1.75), 2e(1), 3i(2.5), 3e(2), 4i/e(3), 5(1.5) versus 1(1), 2i(1-1.5), 2e(0.5), 3i(1.5), 3e(1), 4i(2-2.5), 4e(1.5-2), 5(0.5)], and by showing a brown facial mask from the snout, under the loreal region, to the tympanum, and by the presence of (usually) one very conspicuous moon-like spot on the back of each flank, close to the pelvic region and the hindlimbs. From B. wittei , it differs in femoral gland dimensions and position (see Fig. 4 ), ovoid tongue (vs. bifid), slightly longer hindlimbs with tibiotarsal articulation reaching between the eye and the nostril (vs. reaching the anterior corner of the eye), less distinct inner metatarsal tubercle, webbing formula, and in coloration. Blommersia wittei has a proportionally smaller tympanum than both B. nataliae sp. nov. and B. transmarina (mean ratio TD/SVL 0.068 ± 0.007, vs. 0.081 ± 0.009 in B. transmarina and 0.080 ± 0.010 in B. nataliae sp. nov.).

Description of the holotype (Fig. 2 ). Male specimen in good state of preservation. Part of the left thigh taken for genetic analyses. SVL = 18.6 mm. The body is slender; the head is slightly longer than wide but not wider than the body. Snout slightly pointed and rounded in lateral views with protuberant nostrils directed laterally, nearer to the tip of snout than to eye; canthus rostralis indistinct and straight; loreal region straight; tympanum distinct and rounded, with a diameter of 60% of the eye diameter; supratympanic fold present and slightly distinct behind the tympanum, but indistinct in its anterior part between the eye and the tympanum; tongue slender and ovoid, slightly notched posteriorly but not bifid; vomerine teeth present but very inconspicuous and very small, hard to see, and not grouped; maxillary teeth rudimentary; choanae rounded. The arms are slender with distinct, single subarticular tubercles, the inner and outer metacarpal tubercles distinct, the fingers without webbing, and the relative length of the fingers is 1<2<4<3; terminal finger discs are enlarged and nuptial pads absent. Hindlimbs are relatively robust; the tibiotarsal articulation reaches between the eye and the nostril when the hindlimb is appressed along the body; the lateral metatarsalia are separated; the inner metatarsal tubercle is small and the outer distinct; toe discs are enlarged, and the webbing between toes weakly developed [1(1), 2i(1.75), 2e(1), 3i(2.5), 3e(2), 4i/e(3), 5(1.5)]. The skin on the dorsal surface is smooth without folds or ridges. The ventral skin is uniformly smooth. Femoral glands are very distinct in life, as well as after ethanol preservation, in external view.

Coloration of the Holotype (Fig. 2 ). In life, the overall color is creamy light brown with golden spots on the flanks, arms, and legs. It shows a thin yellowish line from the midpoint between the eyes to the vent. The legs are slightly darker brown and bands are visible. It shows a dark brown spot on the flanks and a characteristic larger moon-like spot on each flank’s back close to the pelvic region and the hindlimbs. It presents a dark brown facial mask that covers from the snout, under the loreal region, to the tympanum (see Fig. 2 ). The loreal region, as well as the outer iris periphery, shows a thin golden-colored line. The pupil is black and the inner iris area dark brown, while the outer iris area is golden with dark reticulations. The throat is brownish. The belly is light brown with some whitish, silver, and gold spots. The femoral glands are oval with a yellowish coloration and 9-10 circular internal rounded structures. After eight years in preservative, the back shows a creamy brown coloration that gets lighter towards the sides of the body, but the golden spots and dorsal line are lost. Ventral coloration is light brown without evident golden spots. The moon-like brown spot in the posterior part of the flanks is still evident, as well as the small ones on the flanks behind the arms. The femoral glands are whitish.

Variation.

The measurements of the holotype and paratypes are provided in Table 1 . Sexual dimorphism is apparent in several characters: males present distinctive femoral glands, females are larger than males [males: median ± SD SVL= 18.5 ± 0.8 mm (min-max=17.9-20.5); females: 20 ± 1.5 mm (min-max=19.6-23 mm)]. The color pattern is rather homogeneous, but females show an overall much creamier coloration than males, which are slightly darker. Both males and females show the characteristic brown rounded moon-like spot on the posterior flanks of the body, as well as some blotches on the lateral body sides behind the arms of variable size and shape. Vomerine teeth are more evident in specimen DRV6854 (MNCN50447), but only on one side of the vomer, and in DRV6855 (MNCN50448) and DRV6808 (MNCN50451) on both sides and more evident than in the holotype. Female DRV6855 (MNCN50448) lacks the moon-like blotch in the posterior side of the body, but shows a large circular one behind the arms. Female DRV6808 (MNCN50451) shows a similar pattern, but with a smaller blotch. Female DRV6868 (MNCN50450) shows a constellation of small rounded to irregular dark blotches from behind the arms to the inguinal region.

Natural history of Blommersia nataliae sp. nov.

The species was found on the ground and in its breeding places: cut bamboo trunks filled with water (Fig. 5 ). There, we observed several males waiting for females to reproduce the night of 28th November 2012, with a temperature of 24.6 °C. No frogs were seen in the breeding places during the day. No call was ever heard during reproductive periods despite several attempts and leaving a digital recorder running for two hours at a breeding spot with active frogs at night, while B. transmarina and B. nauticus were calling. The clutches were placed on the bamboo’s inner walls above the water, but only a few eggs seemed to be fertilized and showed embryonic development. We counted three clutches of 42, 43, and 22 eggs on the walls of cut bamboo trunks in November 2012 at Mont M’Sapere. Females seem to deposit several unfertilized eggs in the water that can serve as food for the tadpoles, but more research is needed to disentangle the species’ reproductive strategy. Individuals were seen during the day on the ground in the forest leaf litter, mixed with B. transmarina . No frogs were ever seen in other microhabitats like swamps, ponds, streams, or similar water bodies, where B. transmarina reproduces. The species reproduces during the rainy season if the bamboo holes are filled with water. We observed clutches and tadpoles in November-December 2012 and April 2014. In some years with little rain (e.g., November 2019), we observed the frogs, but all usual reproduction sites were empty of water with no clutches or tadpoles. The scarcity of rain may strongly affect this species in the near future, limiting its possibility to reproduce.

Distribution.

Initially found on the slopes of Mont M’Sapere only where there is still forest present and giant bamboos, between 235 m a.s.l. and 409 m a.s.l. (2012, 2014, and 2019). In the 2014 expedition, we also found the new species at Mont Bénara (12.8712°S, 45.15614°E, 317 m a.s.l.) in a forested place with fewer bamboo stands available, but few specimens. It is possible that the species breeds in other microhabitats (e.g., tree holes) as in the places where it occurs at Mont Bénara there are not many bamboo stands available, but this hypothesis needs to be confirmed. After several trips and visits around the whole entire main island of Mayotte and surrounding islets, with very intense fieldwork, we have not found it anywhere else, and the habitat appears to be degraded for the species.

Conservation.

The new species is only known from two localities and seems restricted to mountain areas where the forest is still present with giant bamboo stands. The area of occupancy is estimated to be less than 10 km2 from the elevation range where it was observed (235 to 409 m a.sl.) and the remaining forest available at the Reserve Forestière de Majimbini (Mont M’Sapere) and the Reserve Forèstiere du Mont Benara ( Dupuy et al. 2019). There are bamboo stands also at lower elevations in degraded forests, but we never detected the species there. The distribution range is extremely small, the habitat is increasingly degraded, the breeding places (broken bamboo trunks) not frequent, and the fact that the observed densities seem to be very low suggest to consider the species as Critically Endangered according to IUCN criteria, in need of urgent conservation actions considering the ongoing degradation of these forest habitats. The impacts of local harvesting of bamboos or fires are not known, but it seems critical for the conservation of the species. The introduction of the chytrid fungus in Mayotte could decimate this species as well as B. transmarina in a few years. The consequences of climate change, such as a reduction in rainfall that fills its reproductive sites, may strongly affect the species as well.

Figures

Figure 2. Dorsolateral and ventral views of the holotype of Blommersia nataliae sp. nov. DRV 6867 (MNCN 50456). Note the color and shape of the femoral glands which are a diagnostic character to distinguish it from its sister taxon B. transmarina.

Figure 3. Dorsolateral and ventral views of Blommersia transmarina DRV 6807 (MNCN 50446), adult male collected at Mont M'Sapere in 2012 by D. Vieites and M. Peso Fernandez. Note the shape and color of the femoral glands.

Figure 4. Scatterplot of relative femoral gland length (FGL / SVL ratio) and the relative distance between the inner edges of the femoral glands (FGD / SVL) in the two new species from Mayotte and their sister taxon Blommersia wittei from Madagascar. Measurements are based on Table 1; and for B. wittei on Vences et al. (2010) and Pabijan et al. (2011). Note the intermediate position of B. wittei between B. transmarina and B. nataliae sp. nov.

Figure 5. Photo of three specimens of Blommersia nataliae sp. nov. during reproduction in a cut bamboo trunk filled with water. On top of the picture, a male can be seen on top of a female, and another male is in the water on the left side of the trunk.