Description
Boophis arcanus is a medium-sized arboreal frog originally described from two females (Glaw et al. 2010) and later informed by five males, of which only two were collected (Reimann et al. 2012). The holotype, a female, has a snout-vent length of 34.3 mm (Glaw et al. 2010). In males, the snout-vent length ranges from 24.3 - 26.6 mm (Reimann et al. 2012). The snout appears rounded in dorsal view and obtuse in profile. It has a relatively large head, wider than its slender body and longer than it is wide. The nostrils are slightly closer to the tip of the snout than the eye. The canthus rostralis is pointed when viewed from the front and concave in dorsal view; the loreal region is also marginally concave. This species has a distinct supratympanic fold and a distinct, rounded tympanum, roughly half the eye’s diameter. The eyes are protuberant with horizontally elliptical pupils. The arms are slender. The hands have single, round subarticular tubercles and no recognizable metacarpal tubercles. The fingers have unmistakably enlarged discs and are moderately webbed, following the webbing formula 1(1.5), 2i(1.25), 2e(1.25), 3i(2), 3e(1.25), 4(1). The relative lengths of fingers is 1 < 2 < 4 < 3. The hindlimbs are slender, and when pressed against the body, the tibiotarsal reaches the snout’s tip. The inner metatarsal tubercle is small and indistinct, and no outer metatarsal tubercle is evident. The toes are separated by well-developed webbing following the formula 1(0), 2i(0.25), 2e(0), 3i(1), 3e(0), 4i(1), 4e(1), 5(0.25). The relative lengths of toes are 1 < 2 < 5 = 3 < 4. The dorsal skin is smooth, with weak granules on the throat and chest and coarse granules on the belly (Glaw et al. 2010).

DIAGNOSIS:

Boophis arcanus can be easily differentiated from the three northern species of the Boophis majori group (B. blommersae, B. marojezensis, and B. vittatus) due to the red coloring on the thighs and feet. Also, B. arcanus is almost uniformly brown and slightly larger than the other B. majori complex species. Bolitoglossa arcanus can also be differentiated from B. miniatus and B. picturatus by its different yellowish iris color and the vertical brown reticulations, which both other species lack (Glaw et al. 2010).

COLORATION:

In life, this species has uniform light brown dorsal surfaces with sporadic dark spots. The chest and belly are white, and there is an uncolored area in the inguinal region. The underside of the legs and thighs are reddish, along with the tips of the fingers and toes. The iris is yellowish with a pattern of dark vertical stripes and a turquoise whitish iris periphery (Reimann et al. 2012). In preservative, distinct dark crossbands become visible: three on its forelimbs, two on its hindlimbs, and one along the jaw. The red on the thighs is still visible (Glaw et al. 2010).

VARIATION:

The female paratype for B. arcanus had similar dorsal surfaces to other described specimens but had a bluish inguinal region. The iris was more silvery than yellow, and the iris periphery was blue (Glaw et al. 2010).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Madagascar

View distribution map in BerkeleyMapper.

Boophis arcanus has a minimal distribution and has only been found in the Ranomafana region of Madagascar. Its elevation range is 500 - 1300 meters above sea level. This region contains a section of undisturbed rainforest habitat in Ranomafana National Park. The rest of the area is rainforest that is fragmented by cultivated fields for agriculture and narrow gallery forests along small streams (Riemann et al. 2012).

Life History, Abundance, Activity, and Special Behaviors
Boophis arcanus is likely in low abundance. Glaw et al. (2010) were only able to collect two specimens when they discovered the species, and Riemann et al. (2012) later observed only five.

Individuals dwell in bushes and trees and have been found at 1 - 2 meters above ground (Glaw et al. 2010; Riemann et al. 2012).

Boophis acranus’s call contains two note types. It starts with type 1, which consists of three pulsed notes, emitted in nonuniform intervals (interval between first and second note is 1437 ms, the interval between second and third note is 374 ms). After a 1262 ms interval, a series of 85 pulsed type 2 notes follows, separated by short intervals of 35 - 72 ms (41.4 ± 11.1 ms, n = 10) at the beginning and only 24 - 32 ms (26.7 ± 2.3 ms, n = 10) at the end of the series. A single type 1 note follows after 81 ms, which ends the call. Type 1 notes show the following characteristics: note duration is 61 – 86 ms (70 ± 11.9 ms, n = 4); number of pulses is 11 – 23 (15.3 ± 5.3, n = 4); dominant frequency range is ca 4000 – 6000 Hz; maximum call energy is 4900 Hz. Type 2 note characteristics: note duration is 37 – 42 ms (39.4s ± 1.8 ms, n = 10) at the beginning and 43 – 55 ms (49.3 ± 3.1 ms, n = 10) at the end; number of pulses is 11 – 14 (12.2 ± 1.0, n = 10) at the beginning and 18 – 25 (21.5 ± 1.8) at the end; note repetition rate is 13.7 notes/s; dominant frequency range is 4600 – 7000 Hz; and four energy maxima, 4800 Hz, 5300 Hz, 5800 Hz, 6500 Hz (Riemann et al. 2012).

Trends and Threats
Long-term population data has not been gathered for Boophis arcanus. However, due to the ongoing habitat loss in Madagascar's Ranomafana region, their population numbers are estimated to be decreasing. This habitat loss results from forest clearances for agriculture and wood harvesting (IUCN 2015).

Possible reasons for amphibian decline

General habitat alteration and loss
Habitat modification from deforestation, or logging related activities
Intensified agriculture or grazing
Habitat fragmentation

Comments

PHYLOGENETIC RELATIONSHIPS:

Boophis arcanus has been placed in the Boophis majori group through phylogenetic analysis on mitochondrial DNA. Its position in the lineage has not been determined, but it does have high genetic divergences from other species in the Boophis genus: 7.3% to B. miniatus, 8.2% to B. piperatus, 8.4% to B. feonnyala, and over 9% to all other species (Glaw et al. 2010).

ETYMOLOGY:

The species epithet, “arcanus”, is Latin for “hidden” or “secret”. The species authority picked this name because the species is difficult to identify solely on morphology, and because Glaw and his team were only able to locate two specimens despite intensive searching (Glaw et al. 2010).

References

Glaw, F., Kohler, J., De La Riva, I., Vieites, D.R., Vences, M. (2010). "Integrative taxonomy of Malagasy treefrogs: combination of molecular genetics, Bioacoustics and comparative morphology reveals twelve additional species of Boophis." Zootaxa, 2383, 1-82. [link]

IUCN SSC Amphibian Specialist Group. 2015. "Boophis arcanus". The IUCN Red List of Threatened Species 2015: e.T49381365A49381418. https://dx.doi.org/10.2305/IUCN.UK.2015-4.RLTS.T49381365A49381418.en. Downloaded on 19 February 2021

Riemann, J. C., Ndriantsoa, S. H., Vences, M., Roedel, M. O., Glos, J. (2012). "Advertisement call and male morphology of the Malagasy treefrog Boophis arcanus from the Ranomafana region, south-eastern Madagascar." Zootaxa, 3250(1), 66-68. [link]

Species Account Citation: AmphibiaWeb 2021 Boophis arcanus <https://amphibiaweb.org/species/7453> University of California, Berkeley, CA, USA. Accessed Sep 12, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 12 Sep 2024.

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