Description
Mini mum is a miniaturized frog that was previously listed as part of the Stumpffia genus. The snout vent length in males is 8.2 - 9.7 mm, and 11.3 mm for one female specimen. The head length is about one fourth of the snout vent length, and the head is wider than it is long. The snout is rounded in the dorsal view and pointed in the lateral view. The nostrils of M. mum are located slightly closer to the eyes than the tip of the snout. The nostrils are directed laterally and not protuberant. The canthus rostralis is straight and indistinct. The loreal region is vertical and flat. Mini mum has a round pupil and an eye diameter that is about one third of the head width. The tympanum is round, indistinct, and around 49% of the eye diameter. The supratympanic fold is absent. There are no distinct dorsolateral folds. The skin on the dorsum and venter is smooth (Scherz et al. 2019).

The forelimb is slender and its length (sum of the hand, upper arm and lower arm lengths) is 50% of the average snout vent length. The outer metacarpal tubercle is rounded, while the inner metacarpal is indistinguishable from the reduced first finger. The hand is not webbed, and has single subarticular tubercles that are only distinct on the third finger. The first, second, and fourth fingers of M. mini are all strongly reduced, while the third finger is broadened at the base. The relative finger lengths are 1 < 4 < 2 < 3. The finger tips are not expanded into discs (Scherz et al. 2019).

The hindlimbs are also slender, and its length (sum of foot, thigh, and tibiofibular lengths) is about 150% that of the snout vent length. The tibiofibular length is 50% of the snout vent length. The lateral metatarsalia are strongly connected, and the inner metatarsal tubercle is indistinguishable from the completely reduced first toe. The outer metatarsal tubercle is absent. The toes are not webbed, and the first toe is absent. The second and fifth toes are strongly reduced, and the relative lengths for toes in M. mini is 2 < 5 < 3 < 4 (Scherz et al. 2019).

All members of the genus Mini are similar to species of the genus Stumpffia. However, M. mum has curved clavicles, which are not present in Stumpffia species (S. contumelia and S. obscoena do not have clavicles, and S. tridactyla has straight or absent clavicles). Mini mum also differs from most Stumpffia frogs through its fingers and toes. Fingers 1, 2, and 4 are strongly reduced and toe 1 is absent, distinguishing M. mum from all Stumpffia frogs except S. tridactyla, S. contumelia, and S. obscoena. Within the Mini genus, M. mum possesses a strong lateral color border that is weak or absent in M. scule and M. ature, respectively (Scherz et al. 2019).

Mini mum can also be diagnosed by call. Its calls are similar to those of S. contumelia, S. miery, S. obscoena, and S. tridactyla. However, M. mum calls are longer in duration (duration 74.8 ± 7.0 ms) and higher in frequency (8089 ± 140 Hz) than S. contumelia (duration 42 ± 4 ms and frequency 7493 ± 50 Hz). Mini mum has shorter calls (duration 74.8 ± 7.0 ms) with a lower frequency (8089 ± 140 Hz) when compared to S. obscoena (duration 144 ± 8 ms and frequency 8361 ± 69 Hz). Mini mum has a slightly longer inter-call interval than S. miery (4299.8 ± 1604.9 ms vs 3102 ± 456 ms). Mini mum calls are shorter in duration (duration 74.8 ± 7.0 ms) and higher in frequency (8089 ± 140 Hz) than S. tridactyla (duration 132 ± 23 ms and frequency 7244 ± 200 Hz) (Scherz et al. 2019).

In alcohol, the dorsum is metallic silver down the center of the trunk with lighter silver on the lateral regions. Mini mum is bluish silver on the head, and has dark oblong markings in the inguinal region. A strong dorsolateral color border is present, and it extends from the side of the head to the legs. The lateral coloration fades from an ebony color to the more burnt umber coloration of the venter. This coloration is especially dark anteriorly, with flecks of beige that get larger posteriorly until the posterior abdomen, which is beige. Dorsally, the arms are silver but become ebony laterally and ventrally. Dorsally, the legs are a spotted cream and grayish brown color, with a darker cloacal region. The legs are brown and flecked with beige ventrally. In life, coloration is browner and less iridescent but otherwise the same. Mini mum has a red iris (Scherz et al. 2019).

The snout vent length ranges from 8.2 - 9.7 mm in males and is around 11.3 mm in females. Specimens with darkened throats are usually males. The species seems to vary little in morphology, however coloration is highly variable. Lateral and ventral colouration is more or less consistently dark brown with light flecks, but rarely the flecks are bright bluish-white laterally. The strength of the flank color border varies from strong to weak. Dorsal colouration also varies from solid tan to mottled beige and dark brown (Scherz et al. 2019).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Madagascar

View distribution map in BerkeleyMapper.

This species has been found only at Manombo Special Reserve, southeast Madagascar. The Manombo Special Reserve consists of an open forest with small trees and a very thick layer of leaf litter. It has an area of 52.66 square kilometers and an elevation of 0 - 100 m above sea level. Mini mum is likely endemic to this region (Scherz et al. 2019).

Life History, Abundance, Activity, and Special Behaviors
Mini mum males call from under dense leaf litter or between roots, separated from other males by several meters. They call during the day. Mini mum calls have a duration of 74.8 ± 7.0 ms with 35 notes and a frequency of 8089 ± 140 Hz. Calls consisting of only one note are emitted regularly without a defined call series. Calls also modulate upward in frequency, starting at around 7000 Hz and rising gradually to 8250 Hz, before ending with a drop in frequency to 7500 Hz (Scherz et al. 2019).

One female specimen examined contained four eggs (Scherz et al. 2019)

Trends and Threats
Mini mum is endemic to only a small region, and has a recommended IUCN threat list status of “Critically Endangered” (Scherz et al. 2019).

Comments
Maximum Likelihood and Bayesian Inference analyses were conducted using the 16S and 12s rRNA mitochondrial genes. These analyses indicate that M. scule is sister to M. ature, and together they form a clade that is sister to M. mum (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 mum is a pun based on the English word “minimum” (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 mum <https://amphibiaweb.org/species/8987> University of California, Berkeley, CA, USA. Accessed Nov 21, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 21 Nov 2024.

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