Description
Mini scule is a miniaturized frog that was previously listed as part of the Stumpffia genus. Mini scule has a snout vent length that ranges from 8.4 - 10.8 mm in males (measurements for females were unavailable). The ventral and dorsal skin are smooth. Distinct dorsolateral folds are absent. The snout is rounded in the dorsal view and squared in the lateral view. The head width is around one third of the snout vent length, and the head length is 26% of the snout vent length. The nostrils are not protuberant and are directed laterally. The nostril snout distance is roughly the same as the eye-nostril distance, and the internarial distance is a little less than double that. The canthus rostralis is indistinct and straight. The loreal region is flat and vertical.The horizontal eye diameter is 36% of the head width, and the eye nostril distance is more than half of the eye diameter. The tympanum has a diameter that’s slightly smaller on average than the nostril-snout distance (both horizontally and vertically). The tympanum is indistinct and round. The supratympanic fold is absent (Scherz et al. 2019).

The forelimb is slender and its length (sum of the hand, upper arm and lower arm lengths) is 55% of the snout vent length. The upper arm length is around one third of the forelimb length. The lower arm length is slightly longer than the upper arm, and the hand length is slightly shorter (around 30% of the forelimb length). The hands are not webbed, and the relative length of the fingers is 1 < 4 < 2 < 3. The finger tips are not expanded into disks (Scherz et al. 2019).

The slender hind limb length (sum of foot length, thigh length, and tibiofibular length) is 154% of the snout vent length. The thigh length is 44% of the snout vent length on average, and the thigh width is 41% of the thigh length. The tibiofibular length is about the same length, if a little smaller, than the thigh length. The tibiofibular width is one third of the tibiofibular length. The tarsal length is 18% of the hind limb length. The foot length is 25% of the hind limb length. The outer metacarpal tubercle is rounded, and the inner metacarpal tubercle is small and indistinct. The maximum length of the inner metacarpal tubercle is 6% of the foot length and the maximum length of the inner metatarsal tubercle is about double the metacarpal measurements. There is no webbing between the toes, and relative toe length is 2 < 5 < 3 < 4, there is no first toe (Scherz et al. 2019).

All members of the genus Mini are similar to specimens of the genus Stumpffia. However, they are all distinguished from Stumpffia by their curving clavicles, and laterally displaced/reduced nasals. Mini scule frogs also have extremely reduced fingers and toes, differentiating it from all Stumpffia species except S. tridactyla, S. contumelia, and S. obscoena. Mini scule differs from these three species in that it lacks a strong lateral colour border, which is present in S. tridactyla, S. contumelia, and S. obscoena. Mini scule also has curved clavicles, whereas clavicles are absent in S. contumelia and S. obscoena, and straight or absent in S. tridactyla. Calls between M. scule and several species of the Stumpffia genus are very similar. The calls of M. scule are most similar to S. gimmeli, S. larinki, and S. tridactyla in call duration, but they are higher in dominant frequency than S. gimmeli and S. larinki, and lower in dominant frequency with a longer inter-call interval than S. tridactyla (Scherz et al. 2019).

Within the genus Mini genus, M. scule can be distinguished from M. mum by a less distinct lateral color border. Mini scule calls differ significantly from M. mum. For example, calls from M. scule have a lower frequency of around 6675 Hz and M. mum calls have a higher frequency of 8089 Hz. Mini scule also has a longer call duration of about 108 - 140 ms, while call duration of M. mum is 57 - 87 ms. Inter-call intervals also vary greatly, with M. mum having a much longer inter-call interval. Mini scule can be distinguished from M. ature by its smaller body size (14.9 mm vs 10.0 mm). Mini scule also has a longer relative hindlimb length that is 154% of its snout vent length compared to M. ature with 118% (Scherz et al. 2019).

In preservative, the dorsum is metallic silver over all the body, except for in the inguinal region and the posterior surface of the thigh where it is brown. The side of the head is dark brown, but becomes increasingly flecked with cream posteriorly. Coloration of the venter and lower lateral area is cream flecked with brown. The brown is most densely speckled on the anterior abdomen, and least densely speckled at the posterior abdomen. On the ventral surfaces of the legs, the flecking is similar to ocelli. Between the dorsal and ventral colouration there is a reasonably distinct color border that runs the length of the flank. In life, the coloration is the same as in preservative, except with a bronze dorsal surface instead of silver. In life, the iris is rust red (Scherz et al. 2019).

The species seems to vary little in morphology, however coloration is highly variable. Some frogs have a steelier color, or dark markings in the inguinal region. Some frogs have a broad burnt umber crossband on its thighs and shanks, which was absent in most other individuals of the species (Scherz et al. 2019).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Madagascar

View distribution map in BerkeleyMapper.

Mini scule has only been found in Sainte Luce, southeast Madagascar. The species seems endemic to only this small region. However, in Mandena, Vohimena mountains and the southern Anosy mountain chain, there have been records of a similar species, Stumpffia tridactyla, which could possibly refer to M. scule. Similarly, Stumpffia tetradactyla, which has been found southeast from Tsitongambarika could also refer to M. scule. A frog from Nahampoana that resembles M. scule is another possibility. In general, M. scule lives in deep leaf litter with semi-permanent water bodies such as shallow and slow-moving forest streams (Scherz et al. 2019).

Life History, Abundance, Activity, and Special Behaviors
Mini scule calls consist of a single note and are emitted at regular intervals without defined call series. Calls were recorded at an air temperature of 30.4°C. Calls weren’t very frequency modulated with a frequency of around 6675 Hz and a call duration of about 108 - 140 ms. Mini scule calls during the day from concealed positions on adjacent stream banks (Scherz et al. 2019).

Trends and Threats
The current estimated Area of Occupancy for M. scule is less than 10 square km. Additionally, the forest in this area is threatened and declining. As a result, this species will likely be classified as "Critically Endangered" (Scherz et al. 2019).

Comments
Maximum Likelihood and Bayesian Inference analyses were conducted using the 16S and 12s rRNA mitochondrial genes. They was found that M. scule is sister to M. ature, and together they form a clade that is sister to M. mun (Tu et al. 2018, Scherz et al. 2019).

The genus name is derived from the English prefix "mini-", meaning a small version of an object. The full name Mini scule is a pun based on the English word “miniscule” (Scherz et al. 2019).

References

Scherz, M. D., Hutter, C. R., Rakotoarison, A., Riemann, J. C., Rödel, M. O., Ndriantsoa, S. H., et al. (2019). "Morphological and ecological convergence at the lower size limit for vertebrates highlighted by five new miniaturised microhylid frog species from three different Madagascan genera." PLoS ONE, 14(3). [link]

Tu, N., Yang, M. H., Liang, D., Zhang, P. (2018). "A large-scale phylogeny of Microhylidae inferred from a combined dataset of 121 genes and 427 taxa." Science Direct, 126, 85-91. [link]

Species Account Citation: AmphibiaWeb 2022 Mini scule <https://amphibiaweb.org/species/8988> University of California, Berkeley, CA, USA. Accessed Apr 18, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 18 Apr 2024.

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