Description
The snout-vent length of Allobates magnussoni ranges from 16.09 - 19.59 mm for males and 17.97 - 20.84 mm for females. The head is shorter than wide and the snout from above is round or truncated and bluntly round from the side. The tip of the snout extends past the lower jaw and is almost half the length of the head. The distance between eyes is 44% of the head width. The distance from the eye to the nostril is about three-quarters the length of the eye. The nostrils open post-laterally. The tympanum is round and inconspicuous. It has a rounded snout with the tip extending past the lower jaw anteriorly. Males do not have vocal sacs or slits. Both the dorsal and ventral skin is smooth, with the exception of small, scattered tubercles on the urostyle region. The forearms are more robust than the upper arm. Relative finger lengths are III > I > II = IV and fingers I and III are swollen but all fingers are unwebbed and unfringed. The tips of the fingers expand in to moderate discs with distinct dorsal scutes. The tubercle on the palms is large and round. The tubercle on the thenar is half the palmar tubercle. Subarticular tubercles are found on all fingers with fingers I, II, and IV having one each and finger III having two. The hindlimb is robust and relative toe lengths are IV > III > V > II > I. There is rudimentary webbing only basally between toes II - III and III – IV and no lateral fringes. The toe pads are moderately expanded. The inner metatarsal tubercle is oval and the outer is round. There is no median metatarsal tubercle. There is a weak metatarsal fold. The tarsal keel is tubercal-like and curves strongly at the proximal end. The keel is connected to the proximal edge of the inner metatarsle tubercle by a fold. There is one subarticular tubercle on toes I and II, two subarticular tubercles on toes III and V, and three on toe IV. The basal subarticualr tubercle on toe IV is indistinct (Lima et al. 2014).

In the dorsal view, tadpoles are ellipsoid and from the side appear slightly flattened. The body is wider than deep. The tail is twice as long as the body. From all angles, the snout is bluntly rounded. The eyes are located dorsally and directed laterally. The nostrils are small and located dorsolaterally and directed anterolaterally, with an unornamented, fleshy ring on the inner margin of the nostrils. The spiracle extends 1.04 mm from the body just behind the midsection and on the left side (sinstral). The vent tube ranges from 1.22 – 1.26 mm and opens dextrally. The intestinal coils can be seen and are more dominate on the left of the body near the spiracle. The fins of the tail have a slight arch and dorsal and vental fins have similar heights at mid-tail. The oral apparaturs is antroventral and emarginate. It ranges from 1.90 – 2.04 mm wide. There are 12 or 13 short round papillae on the lateral margin of the anterior labium. The posterior labium projects anteriorly, obscuring the posterior tooth rows, and is surrounded by 32 – 35 short papillae that range in shape form pyramidal to slightly elongate. There are no submarginal papillae. The lower jaw sheath is V-shaped and deeper than the upper jaw sheath with both upper and lower sheaths serrated (Lima et al. 2014).

Allobates magnussoni can be distinguish from most other Allobates species by the combination of location and a distinct hourglass-shaped mark on the dorsum. Of the more similar species, A. magnussoni can be differentiated form A. femoralis, A. hodli, and A. myersi by the absence of dorsal flash marks of red or yellow on the thigh and absence of black and white ventral marbling. A dark, distinct, bat-shaped mark followed by a diamond and a triangle or another bat-shape mark between the eyes distinguishes the species from A. marchesianus, A. caeruleodactylus, A. conspicuus, A. fuscellus, A. masniger, A. sumtuosus, A. vanzolinius, A. nidicola, A. subfolionidificans, A. paleovarzensis, A. grillisimilis, and A. amissibilis. The species is further differentiated from those species by either its larger size or the absence of continuous, solid, pale ventrolateral and dorsolateral strips, and the presence of a distinct oblique lateral bar. The lack of dorsal cross-like patterns differentiates the species from A. olfersioides and A. goianus (Lima et al. 2014).

When preserved, A. magnussoni can be most easily confused with A. brunneus, A. crombiei, A. gasconi, A. undulatus and A. flaviventris because they all have hourglass markings on the dorsum. The throat coloration can help differentiate it from A. brunneus, by male A. brunneus having cream to yellowish throats in preservative and females having white throats. Additionally in A. magnussoni there is a larger internarial distance, no head sexual dimorphism, and a larger difference in relative finger lengths of fingers I and II. Allobates magnussoni males have a gray (in preservative) and gray-violet (in life) throat, and both sexes have a distinct oblique lateral bar and lack or have a very diffuse ventrolateral stripe that distinguishes it from A. crombiei. From A. gasconi, A. magnussoni differs by being larger in size, having an unswollen third finger, having a diffuse or absent ventrolateral and dorsolateral strip, and having a distinct oblique lateral bar. From A. undulatus, A. magnussoni differs by geographic location, smaller body size, having a dark brown lateral stripe on the flank that is broken by a distinct pale-brown oblique lateral bar at the mid-body and edged on ventral size with a diffuse, iridescent-white ventrolateral line or series of spots. From A. flaviventris, A. magnussoni differs by either lacking or having diffuse ventrolateral stripes in life, the distinct oblique lateral bar, having basal webbing between toes, advertisement call, and morphometric measurements (Lima et al. 2014).

Allobates magnussoni tadpoles can be differentiated from the tadpoles of Allobates caeruleodactylus, A. marchesianus, A. grillismilis, and A. brunneus by having more lateral labial papillae and shorter posterior labial papillae. The lack of transverse bars on the tail on A. magnussoni differentiates it from A. caeruleodactylus and A. marchesianus. Labial tooth rows allow differentiation from A. sumtuosus, A. granti, and A. brunneus. The lack of a dark brown bark from the eye to the snout, and down to the mid-body differentiates it from A. paleovarzensis. And lastly, being aquatic tadpoles with oral discs and spiracles differentiates A. magnussoni from the terrestrial A. nidicola and A. masiger (Lima et al. 2014).

In life, this species is dorsally cryptically colored various shades of brown to blend in with the leaf litter. The dorsum has a distinct dark brown hourglass marking from the anterior to mid dorsal side. It consists of three convex sections: the first is approximately bat-shaped between the eyes, the second approximately diamond-shaped, and the third similar to the first but with opposite orientation. The frogs lack or have a diffuse dorsolateral strip. Both the upper arms and dorsal side of legs are light brown. The legs are patterned with dark-brown transverse bars located at the middle section of thighs and shank that line up when the frogs are at rest in the sitting position. The feet have two transverse bars that are dark-brown and may be diffuse. Adult calling males have grayish-violet throat and chest that lighten in color when they are not calling. Males have white abdomens that transition to a translucent bright yellow toward the back and flanks. Females have uniform ventral coloring that is yellow. The ventral side of the limbs ranges from bright to dull yellow depending on the locality. When preserved, the dorsum continues to be various brown shades. The hourglass shape may become lighter. The upper arm may become cream colored but the top of the foot is the same color as the dorsum. There may be a diffuse ventrolateral strip in the form of irregular or wavy white spots. There is a cream strip below a dark brown lateral band. The band is broken at mid-body by a distinct oblique light brown bar. The dorsal half of the tympanum is dark-brown while cream on the ventral half. Females in reproductive state have a cream throat and ventrum without melanophores. Reproductive males vary in vocal sac color and upper chest. And lastly, there is a cream-colored paracloacal mark in all specimens (Lima et al. 2014).

Tadpoles, in life, have pale iridescent blotches on the backs and sides of the body and on the tail. In preservative, most of the body is cream colored and spotted with brown clusters of melanophores. The posteroventral region of the body is transparent and the intestines can be seen through the skin. There is a dark brown area on the back that highlights the base of the caudal musculature, which is cream colored. The caudal fins are transparent with scattered irregular brown melanophores (Lima et al. 2014).

The dorsal coloration can vary between individuals. The dorsolateral stripe can be diffuse or absent. In specimens from Parque Nacional da Amazônia, the ventrolateral line is absent or diffuse as small irregular iridescent-white spots present on flank. In individuals from Treviso and Jamansim, the ventrolateral line is diffuse and appears as a series of wavy, elongate, interconnected iridescent-white spots. Males have a slightly wider finger III and slightly longer legs than females (Lima et al. 2014).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Brazil

View distribution map in BerkeleyMapper.

The habitat of A. magnussoni seems to be restricted to the south of the Amazon River, in the Tapajos River basin, Brazil. The species can be found in forested areas along the bank of the Tapajos River’s central and lower course. They occur in forests that do not experience seasonal flooding, but are also areas managed for logging. On the left bank of the Tapajos River, they occur in Parque Nacional da Amazonia. On the right bank of the river, there have been samples collected from Treviso and Jamanxim (Lima et al. 2014).

Life History, Abundance, Activity, and Special Behaviors
Individuals of this species are generally active in the early morning and late afternoon, with males calling from 5:30 to 9:30 am and from 4:30 pm until dusk. Males produce both advertisement and territorial calls. The main advertisement calls consisted of continuous short tonal notes that are separated by routine quite intervals. There may be a slight ascending frequency modulation during the call. Across two sites, the note duration range from 0.047 – 0.104 milliseconds, the number of notes per second ranged from 1.30 – 2.56, and the silent period lasted 0.347 – 0.811 seconds. The peak frequency of notes ranged from 4273.0 – 4867.3 Hz, the low frequencies were from 3809.1 – 4430.8 Hz, and the highest frequencies were from 4484.9 – 5132.8 Hz. A second advertisement call was characterized by starting as note pairs that shift after 10 – 20 seconds to the continuous call. During these note pairs, the note emission rate was 2.3 – 2.9 notes per second and did not have as wide of a range in frequency as the continuous section (Lima et al. 2014).

Mating occurs when females approach calling males, who then leave folded leaf nests to meet the female. The male returns to the nest with the female following. After some time, the male then leaves the female in the nest and the female remains for a short period before leaving herself. Males are frequently found close to egg clutches. Tadpoles can be found in nests on folded leaves in leaf litter and in small headwater streams inhabited by a large number of adults (Lima et al. 2014).

Trends and Threats
Allobates magnussoni is distributed on the Tapajos River drainage, a region historically impacted by deforestation. Several government projects associated with hydropower and river damming could further impact the habitat. Though the type locality occurs in Parque Nacional da Amazonia on the west bank of the Tapajos River, there is no information about its occurrence in the east bank. There is also no information available about population trends on either parts of the species distribution (Lima et al. 2014).

Possible reasons for amphibian decline

General habitat alteration and loss
Habitat modification from deforestation, or logging related activities
Dams changing river flow and/or covering habitat

Comments
The species authority is: Lima, A.P., Simoes, P.I., Kaeffer, I.L. (2014). “A new species of Allobates (Anura: Aromabatidae) from the Tapajos River basin, Para State, Brazil.” Zootaxa, 3889(3): 355-387

Based on a maximum likelihood analysis of a 481 base pair section of the 16S rDNA gene, A. magnussoni was split from the closely related species A. brunneus. Thus some specimens of A. magnussoni may be labeled either Allobates brunneus or Colosthethus brunneus (Lima et al. 2014).

The species name is dedicated to Dr. William (Bill) E. Magnusson from Instituto Nacional de Pesquisas da Amazônia, who has inspired love and understanding of the Amazon forest and its frogs in many students (Lima et al. 2014).

Allobates magnussoni demonstrates the need for multiple call samples to be recorded before describing a species’ call as this species has two types of advertisement calls of which one is more similar to A. brunneus (Lima et al. 2014).

Species Account Citation: AmphibiaWeb 2015 Allobates magnussoni <https://amphibiaweb.org/species/8262> 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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