Description
Brachycephalus actaeus is a small frog with a snout-vent length ranging from 9.2 - 10.8 mm and an average of 10.1 mm in males. The snout-vent length range in females is 11.1 - 12.4 mm with an average of 11.7 mm. The body is robust and toad-like in nature. The head is wider than it is long and the head's length is approximately 19% of the snout-vent length. The snout is rounded in both the dorsal and ventral view, and has protruding nostrils. The canthus rostralis is not clearly defined. The area or region between the eyes and nostrils is slightly curved inward. The eyes are protruding from the skull both laterally and dorsally with an eye diameter of 72% the length of the head. The tympanum is missing. The lips are crescent shaped. The vocal sac does not expand on the external part of the body, but vocal slits are in existence. The tongue is longer than it is wide and the posterior part of the tongue does not stick to the bottom of the mouth. There is no presence of vomerine teeth. The arms and forearms are relatively thin. On the hands, fingers I and IV are smaller and less distinct than finger II while finger III is larger and sturdier. All fingertips are rounded with the exception of fingertip III, which is pointed. The relative fingers lengths, from smallest to largest, are IV, I, II and III. There is no evidence of subarticular tubercles, and both the inner and outer metacarpal tubercles are absent. The legs are semi-short and relatively strong. The thigh length is 41% of the snout-vent length and the tibia is 86% the length of the thigh. Toes I and V are not visually identifiable from the exterior of the body, toe II is very small and toe III is also short but recognizable. The last toe, toe IV is the largest and very evident. Relative toe lengths, from smallest to largest, are II, III and IV. The toe tips of toes II and III are round in appearance but toe IV is pointed. Much like the hands, both subarticular tubercles and inner and outer metatarsal tubercles are non-existent. The skin on the head, dorsal and ventral surface of arms, pectoral region and gular region are smooth. The skin on dorsolateral and dorsal surface of legs and around the cloacal opening are rough and granular. The skin on the belly and ventral side of legs are granular (Monteiro et al. 2018).

Brachycephalus actaeus has a distinct toad-like, or bufoniform, body and possesses an orange background color. This makes it distinct in comparison to B. didactylus, B. hermogenesi, B. pulex, and B. sulfuratus who all possess leptodactyliform bodies and a brown background color. The darker green coloration on B. actaeus’s dorsal side is close to that of B. albolineatus, who also shares a similar darkish green colorization. However, the same green coloration can be used to differentiate B. actaeus from B. boticario, B. coloratus, B. ferruginus, B. fuscolineatus, B. izecksohni, B. leopardus, B. mariaeterezae, B. quiririensis, B. pernix, B. pombali, B. tridactylus, and B. verrucosus, who all poses bright orange or yellow coloration on their dorsal side. The body size of B. actaeus is a differentiating factor as it has a slightly smaller snout-vent length of 9.2 - 10.8 mm in males and 11.1 - 12.4 mm in females in comparison to B. ferruginus, which has snout-vent length in males of 11.6 – 12.5 mm and 13.0 – 14.5 mm in females, B. pernix, which has an snout-vent length of 12.0 – 13.3 mm in males and 14.1 – 15.8 mm in females, B. pombali, which has an snout-vent length of 12.6 – 13.9 mm in males and 14.6 – 15.3 mm in females, B. coloratus which has an snout-vent length of 10.3 – 10.6 mm in males and 12.2 – 13.3 mm in females, B. izecksohni, which has an snout-vent length of 10.3 – 12.1 mm in males and 12.5 – 13.1 mm in females, and lastly B. tridactylus, which has an snout-vent length of 10.6 – 11.6 in males and 13.5 – 13.8 mm in females. Brachycephalus actaeus also has a rounded snout when viewed dorsally or laterally that differentiates it from B. brunneus as it has a more pointed snout when viewed dorsally. Brachycephalus actaeus also can also be differentiated from B. leopardus, which has a moderately shorter snout when viewed dorsally and laterally, and lastly, from B. quiririensis, which has snout that ends in a rounded point. Brachycephalus actaeus is also missing a hyperossified skull and skeleton that separates it from B. darkside, B. ephippium, B. garbeanus, and B. margaritatus because they all exhibit hyperossification of the skull, skeleton and have a bony shield on their dorsal side. The lack of hyperossification further differentiates B. actaeus from B. alipioi, B. atelopoide, B. bufonoides, B. crispus, B. guarani, B. nodoterga, B. pitanga, B. toby, and B. vertebralis, which all exhibit an intermediate condition of hyperossification. Brachycephalus actaeus also has a smaller fenestra farther away from the epicoracoid, which helps differentiate B. actaeus from B. brunneus, B. coloratus, B. ferruginus, B. izecksohni, and B. pombali, all of whom possess pectoral girdles with larger fenestra located closer to the epicoracoid. Brachycephalus actaeus also has two prepollical elements that differentiates it from B. albolineatus, B. coloratus, B. curupira, B. ferruginus, and B. pombali who only have a single prepollical element and B. izecksohni , which doesn’t have a prepollical element. Lastly, B. actaeus makes high frequency notes that are made of only two pulses that differ from similar species in the genus who have low frequency advertisement calls (Monteiro et al. 2018).

In life, the overall background surface of B. actaeus is green or orange with dark green patches. It has black irises. When viewed dorsally, a barely visible dark brown stripe extends from between the eyes to the rear end of the vertebral column. All arms and legs are dark green including fingers III, IV and toe number IV. The rest of the fingers and toes are orange in color. When viewed ventrally, the tip of the snout, lower lip and corners of the mouth are orange as well. Dark brown patches are located on the throat and the area surrounding the cloaca. Lastly, sporadic brownish spots can be found on the belly, arms, fingers, legs and toes (Monteiro et al. 2018).

In preservative, the overall body, including the arms, legs, fingers III and IV and toe IV are varied colors of brown. The other fingers and toes are white. When viewed ventrally, the tip of the snout, lower lip and corners of the mouth are white. Also, when viewed ventrally, the general background color is white. Brown patches are still visible on the throat, area surrounding the cloaca, side of the body and ventral side of the legs. Sporadic brown spots are visible and spread over the belly, legs, fingers and toes (Monteiro et al. 2018).

In the only juvenile specimen, the body color is brown overall and doesn’t have the generally orange background that the adults have. In the juvenile specimen, the dark brown dorsum is also covered by brown and red spots. The ventral surface of the body is also to a small degree transparent with a belly that is mostly white with a large brown irregular patch. When in preservative, the orange color turns to either a light cream or white and dark brown replaces brown and green colors (Monteiro et al. 2018).

The skin on the dorsal side varies as it can be smooth or rough. The green color on the dorsal side of the body can also vary with some individuals having green completely covering the dorsal side of the body. The brown vertebral stripe can be evident and can vary in width with some individuals having it cover the entire dorsum and others may just possess patches on the vertebral column and head. The orange color around the eyes can resemble a mask and, in most individuals, the tip of the snout is also orange. Some specimens have dark patches exclusively in the cloacal area while others have them only on the throat, belly, or side of the body. The extent to which the gular region is predominately orange can also vary (Monteiro et al. 2018).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Brazil

View distribution map in BerkeleyMapper.

Brachycephalus actaeus is the only known member of the “pumpkin-toadlets” that is found in the lowlands of the northeastern state of Santa Catarina, Brazil. Its habitat is in the leaf-litter of the Southern Atlantic Forest. It can be found in six localities ranging from, near or around sea level up to 250 meters above sea level (Monteiro et al. 2018).

Life History, Abundance, Activity, and Special Behaviors

Brachycephalus actaeus lives in the interior of dense, well-preserved forests. This species is mostly active during the day. All observed male specimens have been observed calling from underneath the leaf-litter in which they live while most but not all female specimens where found underneath leaf-litter.

Reproduction in B. actaeus is thought to be continuous because they can be observed making calls year round. Brachycephalus actaeus are oviparous (Monteiro et al. 2018).

The advertisement call of B. actaeus consists of one short, high-frequency note with two pulses. The vocalizations of B. actaeus males can stimulate its neighbors to call as well (Monteiro et al. 2018).

When threatened, B. actaeus may play dead in a behavior called “thanatosis” (Monteiro et al. 2018).

Trends and Threats
The main threats to the survival of B. actaeus include climate change, rising sea levels and habitat loss mostly attributed to continued construction and urbanization in the coastal region of montane forests. Specifically, seaport construction and rapid expansion throughout northeastern Santa Catarina has disrupted B. actaeus’s habitat. Although B. actaeus occurs at six distinct localities, the instances of this species are limited to established areas of conservation (Monteiro et al. 2018).

The IUCN Red List has no assessment for this species; however, Bornschein et al (2019) analyzed the Brachycephalus species using the IUCN Red List criteria with newer locality information and concluded this species should be listed as Endangered (criteria B1ab(i,iii)+2ab(ii,iii)) based on its small known range, ongoing habitat loss and degradation, and other factors.

Possible reasons for amphibian decline

General habitat alteration and loss
Habitat modification from deforestation, or logging related activities
Urbanization

Comments
Phylogenetic analyses were conducted using the 16S gene. According to the Maximum Parsimony method, B. actaeus is a monophyletic group. However, it forms a polytomy with B. quirirensis, B. olivaceus, B. auroguttatus, B. ferruginus, B. verrucosus. More analyses should be conducted for better resolution of relationships in this clade (Monteiro et al. 2018).

The species name “actaeus” is a Latin word that means “situated on the edge” and was derived from the Latin word "acta", which translates to "shore, coast or beach". The name was given to this species due to its habitat in the coastal lowlands and forests (Monteiro et al. 2018).

Brachycephalus actaeus is the first species of a “pumpkin-toadlet” that has been found to occur in the lowlands of the Atlantic Forest, which makes it very important as it may help researches understand the evolution of the genus (Monteiro et al. 2018).

References

Bornschein, M. R., Pie, M. R., Teixeira, L. (2019). "Conservation status of Brachycephalus toadlets (Anura: Brachycephalidae) from the Brazilian Atlantic rainforest.” Diversity, 11(150), 1-29. doi: 10.3390/d11090150 [link]

Monteiro, J. P. C., Condez, T. H., Garcia, C. A., Comitti, E. J., Amaral, I. B., Haddad, C. F. B. (2018). "A new species of Brachycephalus (Anura, Brachycephalidae) from the coast of Santa Catarina State, southern Atlantic Forest, Brazil." Zootaxa, 4407(4), 483-505.

Species Account Citation: AmphibiaWeb 2022 Brachycephalus actaeus <https://amphibiaweb.org/species/8817> University of California, Berkeley, CA, USA. Accessed Oct 11, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 11 Oct 2024.

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