Description
The body of Blommersia transmarina is slender, with the head wider than the body. The snout vent length for males of B. transmarina ranges from 25.0 - 27.9 mm, averaging 26.3 mm. For females, the snout vent length ranges from 26.9 - 34.5 mm, averaging 31.5 mm. The snout is slightly pointed in the dorsal and lateral views, and its nostrils are directed laterally, are slightly protuberant, and are closer to the tip of the snout than to the eye. The canthus rostralis is distinct and straight. The loreal region is concave. The tympanum is distinct, rounded, and about 73% of the eye diameter. The supratympanic fold is moderately distinct and curved (Glaw et al. 2019).

The arms of B. transmarina are slender, and the subarticular tubercles are singular. The fingers lack webbing, and the relative lengths of fingers are 1 < 2 < 4 < 3. The finger disks are distinctly enlarged. Nuptial pads are absent (Glaw et al. 2019).

The hind limbs of B. transmarina are also slender. When the hind limb is adpressed along the body, the tibiotarsal articulation reaches slightly beyond the snout tip. The lateral metatarsalia are separated, and the inner and outer metatarsal tubercles are present. There is webbing between toes has a formula of 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 the relative toe lengths are 1 < 2 < 3 = 5 < 4 (Glaw et al. 2019).

The skin on the upper surface of B. transmarina is smooth, with no folds or ridges. There are no distinctly enlarged tubercles in the cloacal region, and the ventral skin is smooth as well. However, the femoral glands are distinct (Glaw et al. 2019).

Blommersia transmarina is assigned to the Blommersia genus based on its relatively small size, presence of a singular subgular vocal sac, femoral gland morphology, reproductive methods, molecular analysis, and general similarity to other species of the Blommersia genus. Compared to the other Blommersia species, B. transmarina is the largest. Blommersia transmarina differs from Wakea madinika, which was formerly included in the Blommersia genus, by its much larger size (snout vent length range from 25.0 - 34.5 mm versus 11 - 16 mm, respectively), and presence of vomerine teeth, where W. madinika lacks them. Blommersia transmarina differs from B. angolafa, B. blommersae, B. domerguei, B. galani, B. grandisonae, B. kely, and B. sarotra with its large size, different coloration, advertisement calls, and presence of vomerine teeth. Blommersia transmarina differs from B. variabilis and B. dejongi also with its larger size and advertisement calls, but all three of these species have vomerine teeth and similar coloration. Blommersia transmarina is most similar to B. wittei, as they share a number of distinctive features: similar size, vomerine teeth, separated metatarsalia, similar coloration, and molecular composition. However, B. transmarina is slightly larger, as the male snout vent length of B. transmarina ranges from 25.0 - 27.9 mm, while the male snout vent length of B. wittei ranges from 20.3 - 27.0 mm. Also, B. transmarina has a slightly broader head, longer hands, and longer hind limbs than B. wittei, and finally, because their advertisement calls differ (Glaw et al. 2019).

In preservative, the back of B. transmarina is brown with blackish spots between the eyes, and with several poorly contrasting, elongated dark brown spots. The flanks of B. transmarina are slightly lighter than the back, but no color border is present between the flanks and the back. The hind limbs are light brown with distinctly darker brown crossbands: four on the femur, three on the tibia, and two on the tarsus. The arms also have darker crossbones, although they are less pronounced. Behind the eye, the head is laterally marked by a conspicuous dark brown streak underneath the supratympanic fold, which includes the tympanum, and ends close to the forelimb insertion. On the ventral side, the coloration is a dirty cream-yellowish with fine indistinct mottling, which is more prominent on the throat. The color on the throat is faded, and shows only traces of silvery-white color. The femoral glands are yellowish, and are slightly lighter than the surrounding skin. The eyes are completely white. Overall, color in life is very similar to preservative, with the exception of the slightly faded throat coloration in preservative, as opposed to the distinct silvery-white throat color in life (Glaw et al. 2019).

There appears to be sexual dimorphism in B. transmarina. Females are distinctly larger in snout-vent length, and size in general. Also, the throats of males have a silvery white color, unlike the females. Coloration does not vary much in B. transmarina, although some individuals may have a slightly lighter more grayish dorsal color with a few white dots on the back. Also, several collected individuals were found to have a Y-shaped brownish marking on the mid-dorsum. Rarely, individuals may have a bright mid-dorsal pale yellow stripe (Glaw et al. 2019).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Mayotte

View distribution map in BerkeleyMapper.

Blommersia transmarina is endemic to Mayotte, a small island belonging to the Comoro Archipelago, with an area of 374 km² and a high density of human population. Blommersia transmarina can be found in slightly degraded natural forest, secondary forest, plantations, semi-open habitats, and gardens (Glaw et al. 2019).

Life History, Abundance, Activity, and Special Behaviors
Calling males of B. transmarina can be heard from vegetation above stagnant or slowly running water after dusk, in February, March, September, and November. Advertisement calls of B. transmarina were recorded at Lac Karehani in March of 2013. The calls consisted of a series of 1 - 30 regularly repeated note pairs, resulting in a call duration ranging from 94 ms - 1,947 ms, with an average of 525.1 ms. Each note pair started with a short note followed by a slightly longer note after a short interval averaging 8.8 ms. The first note of a call was usually indistinct and nearly unrecognizable. Calls were repeated after irregular intervals. In addition to these advertisement calls, a few singular, irregularly pulsed notes were recorded, which are considered to be territorial calls (Glaw et al. 2019).

Blommersia transmarina breeding habitats are found in a large variety of bodies of water, including ponds, swamps, canals, water-filled bamboo holes, and artificial bodies of water, like rainwater barrels. Mating pairs, without amplexus, were found in February and March, and sometimes, more than two individuals were found at the breeding location. Most pairs and individuals were found on leaves above stagnant bodies of water. One individual was found near a freshly-laid clutch of eggs, which was glued to a leaf. On first sight, this appeared to be an exhibition of egg-guarding, but not enough data was collected to support this hypothesis (Glaw et al. 2019).

Tadpoles in various developmental stages, and metamorphosing froglets were also observed in February and March, indicating a prolonged breeding period in B. transmarina. Egg clutches and tadpoles are similar to those of other members of the Blommersia genus (Glaw et al. 2019).

Comments
The species authority is: Glaw, F., Hawlitschek, O., Glaw, K., Vences, M. (2019). "Integrative evidence confirms new endemic island frogs and transmarine dispersal of amphibians between Madagascar and Mayotte (Comoros archipelago).” The Science of Nature 106(19): 1–14 doi.org/10.1007/s00114-019-1618-9.-B251-0690E96F6E47

Phylogenetic analysis was done on the mitochondrial 16S rRNA gene using Bayesian Posterior Probability. Specifically, the GTR+G substitution model was used for Blommersia cladogram alignment. From the analysis, B. transmarina was found to be a sister species of B. wittei. The clade of B. transmarina and B. wittei was sister to B. sp. Ca5, a candidate species for the Blommersia genus. The clade formed by these three species is sister to a clade formed by B. grandisonae, B. angolafa, B. sarotra, B. key, and B. sp. Ca10, another candidate species for the Blommersia genus. Finally, the clade formed by these aforementioned species of Blommersia is sister to a clade formed by the rest of the Blommersia species: B. domerguei, B. blommersae, B. variabilis, B. galani, and B. dejongi (Glaw et al. 2019).

The word “transmarina” is a Latin adjective, meaning “from beyond the sea.” With regard to B. transmarina, this references the successful overseas dispersal of its ancestor from Madagascar to the Comoros Islands (Glaw et al. 2019).

Before becoming a member of the Blommersia genus, B. transmarina was initially meant to be placed in the Mantidactylus genus, and given the species name granulatus. The Mantidactylus genus is comprised of frogs of the mantellid subfamily that is restricted to Madagascar. Since B. transmarina does not inhabit Madagascar, it was relocated to the Blommersia genus (Glaw et Vences 2006).

Blommersia transmarina is one of only two species of the family Mantellidae, that are not endemic to Madagascar. The other species is a member of the Boophis genus: B. nauticus. These two species occur synoptically in Mayotte, an island belonging to the Comoros archipelago near Madagascar. The geographic situation of this island lends credence to the hypothesis that their biota may have dispersed from Africa and Madagascar. The phylogenetic analysis and taxonomic distribution of B. transmarina and B. nauticus indicate that the most recent common exchange was with Madagascar rather than Africa (Glaw et al. 2019).

References

Glaw, F., Hawlitschek, O., Glaw, K., and Vences, M. (2019). ''Integrative evidence confirms new endemic island frogs and transmarine dispersal of amphibians between Madagascar and Mayotte (Comoros archipelago).'' The Science of Nature, 106(19), 1-14.

Glaw, F., Vences, M. (2006). ''Phylogeny and genus-level classification of mantellid frogs (Amphibia, Anura).'' Organisms Diversity & Evolution, 6(3), 236-253.

Species Account Citation: AmphibiaWeb 2020 Blommersia transmarina <https://amphibiaweb.org/species/8999> University of California, Berkeley, CA, USA. Accessed Apr 19, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 19 Apr 2024.

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