© 2003 Dr. Axel Kwet (1 of 2)
The skin on the dorsal and lateral surfaces of the body has shallow warts with corneous spines. There are other scattered spines on the skin of the head and other dorsal surfaces. The skin on the ventrum is finely granulose with spines scattered over the belly. The ventral surface of the thighs is granular with some spines. The cloaca is located at the mid-level of the thighs and directed posteriorly (Cruz and Caramaschi 2003).
The arms are slender and do not have ulnar folds or axillary membranes. The round outer palmar tubercle is of moderate size and the round inner palmar tubercle is small, approximately half the size of the outer. The hand has long, slender fingers with relative lengths of I < II < IV < III that do not have fringes or webbing. Well-developed, round subarticular tubercles can be found, but typically only on fingers III and IV. Supernumerary tubercles can also be found. The tips of the fingers are narrow, rounded, and without discs. The legs are short, robust, and do not have tarsal folds. The thigh is slightly shorter than the tibia and the combination of the two lengths is slightly less than two-thirds the snout-vent length. The oval inner metatarsal tubercle is large and prominent. The outer metatarsal tubercle is about the same size as the inner and rounded. The toes are slender and have relative lengths of I < II < V < III < IV. Similarly to the fingers, the toes do not have fringes and the tips are narrow, rounded, and without discs. However, the toes have basal webbing that barely extends to one-third of the toes. The border of the webbing is indented. The subarticular tubercles of the toes are well developed and subconical and the supernumary tubercles of the toes are poorly developed (Cruz and Caramaschi 2003).
Melanophryniscus dorsalis was at first described by Mertens in 1933 as a subspecies of M. stelzneri. It was distinguished as its own species in 2003 by body morphology and dorsal coloration. It has a slender body compared to M. stelzneri and also lacks yellow points in its dorsal colors. The re-description was made based on preserved specimens. The preserved specimens appear brown dorsally with a pale yellowish brown stripe (Cruz and Carmaschi 2003). Melanophryniscus dorsalis can also be distinguished in life by its vocalization. Compared to other species within the M. stelzneri group, who all have similar calls, M. dorsalis calls consist of longer pulse duration, fewer pulse repetitions, and a relatively higher dominant frequency. Its type A call lasts 1 - 4 second and its type B call lasts 0.4 - 2.6 seconds (Kwet et al. 2005).
In life, the species has a dark black dorsum with bright red splotches and a red mid-dorsal stripe. It does not have yellow spots in the suprascapular or mid-dorsal areas like other closely related taxa. It can, however, have yellow lateral spots, though this is not consistent throughout its range. Its dorsal line also varies within its distribution. While many have a complete dorsal line, or at least a line that is only partially broken up, other specimens within range only have a faint trace of a dorsal line, barely visible between the eyes or above the anus. The ventrum is orange or yellow (Kwet et al. 2005).
In preservative, the background color of the loreal region, dorsum, flanks, and ventrum is dark brown. There is a distinct brown dorsal midline stripe that connects the head to the urostile area and can appear complete or interrupted. The gular region has two small, pale yellow blotches near the corners of the mandible. Yellow coloration can also be found on other areas of the ventral surfaces including on the chest at the arm insertions, belly, limbs, palms, and planters (Cruz and Carmaschi 2003).
Individuals vary in patterning. Some individuals have yellow spots on their flanks and the uniformity and intensity of the middorsal line varies by geographic location (Kwet et al. 2005).
Distribution and Habitat
Within its distribution range, the species occupies open areas and sand dunes. More specifically, it is typically found in grassland and dune vegetation on sandy soil within the coastal region after recent rainfall. Males can be found partially submerged in temporary ponds during the breeding season (Kwet et al. 2005).
Life History, Abundance, Activity, and Special Behaviors
This species reproduces in temporary pools of freshwater (Stuart et al. 2008) that appear in the warmer rainy season from October to March. The frogs are mass breeder and appear in large numbers after a heavy rainfall. Males call from morning to early evening from their partial submersed positions in temporary pools, but quickly stop calling after 1 - 2 days without rainfall (Kwet et al. 2005).
Melanophryniscus dorsalis has two types of advertisement calls. Type A calls are relatively long single note calls with relatively long time intervals followed by the type B call, which consisted of a lasting trill with 100 – 200 notes and relatively short time intervals. At air temperatures of 20 - 24 °C both advertisements calls had a dominate frequency of 2.3 – 3.2 kHz with additional weak harmonic frequency ranges of 4.9 – 6.0 kHz and 7.8 – 8.4 kHz. Type A calls were composed of 6 – 20 unpulsed notes that lasted from 20 – 65 ms with internote intervals of 80 -170 milliseconds. The call occasionally had 5 – 7 pulses with interpulse intervals of 0.5 – 1.0 second. Type B calls had durations of 0.6 – 2.6 seconds with 50 - 180 pulses that lasted 7.0 – 9.5 milliseconds and inter-pulse intervals of 6.5 – 7.5 milliseconds. At temperatures between 20 – 21 °C pulse rates for call type A was 4 – 7 pulses per second and for call type B was 60 – 80 pulses per second. The species is able to change the frequency of their call by up to 800 Hz in a 100 millisecond period during their type B call (Kwet et al. 2005).
An amplectant pair was found with a clutch of 20 – 30 eggs that they attached 5 cm below the water surface to an aquatic plant. When the pair was brought into the lab, they laid an additional 105 eggs that were 1.2 – 1.4 mm in diameter, but which did not complete development (Kwet et al. 2005).
Being part of a taxonomic group known for having toxins, M. dorsalis is thought to have aposematic coloration. It has been observed performing an unken reflex, as have other related species within its taxonomic group (Kwet et al. 2005).
Trends and Threats
Melanophryniscus dorsalis was originally identified as a subspecies of M. stelzneri by Mertens in 1933. Cruz and Caramaschi elevated M. dorsalis to a full species 2003 based on morphology and habitat preferences but kept the species as a member of the M. stelzneri group.
The species epithet, “dorsalis”, is a reference to the dorsal stripe on its back, which is a diagnostic characteristic of this species (Kwet et al. 2005).
Cruz, C.A.G., Caramaschi, U. (2003). ''Taxonomic status of Melanophryniscus stelzneri dorsalis (MERTENS, 1933) and Melanophryniscus stelzneri fulvoguttatus (MERTENS, 1937) (Amphibia, Anura, Bufonidae).'' Boletim do Museu Nacional, N.S., Zool., Rio de Janeiro, 500, 1-11. [link]
Kwet, A., Maneyro, R., Zillikens, A., and Mebs, D. (2005). ''Advertisement calls of Melanophryniscus dorsalis (Mertens, 1933) and M. montevidensis (Philippi, 1902), two parapatric species from southern Brazil and Uruguay, with comments on morphological variation in the Melanophryniscus stelzneri group (Anura: Bufonidae).'' Salamandra, 41(1/2), 1-18.
Stuart, S., Hoffmann, M., Chanson, J., Cox, N., Berridge, R., Ramani, P., Young, B. (eds) (2008). Threatened Amphibians of the World. Lynx Edicions, IUCN, and Conservation International, Barcelona, Spain; Gland, Switzerland; and Arlington, Virginia, USA.
Written by Ashling Quigley (ashlingquigley AT berkeley.edu), UC Berkeley
First submitted 2018-12-05
Edited by Riley Kermanian and Ann T. Chang (2018-12-07)
Species Account Citation: AmphibiaWeb 2018 Melanophryniscus dorsalis: Red-Bellied Toad <http://amphibiaweb.org/species/6185> University of California, Berkeley, CA, USA. Accessed Oct 16, 2019.
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