Three-toed toadlets

(Brachycephalidae)

Class Amphibia

Order Anura

Family Brachycephalidae

Thumbnail description
Small toad-like anurans with reduced number of segments in their digits and a fully ossified pectoral girdle lacking a sternum

Size
0.3–0.8 in (8.5–20.0 mm) snout-vent length

Number of genera, species
2 genera; 6 species

Habitat
Humid forest

Conservation status
Not threatened

Distribution
Atlantic coastal forest of eastern Brazil

Evolution and systematics

No fossils are known. These small anurans were formerly placed in Bufonidae, from which they differ by the absence of a Bidder's organ (a growth of ovarian tissue on the testis). The relationships of the family are unknown, but it has been suggested that brachycephalids are related to Euparkerella, a telmatobiine (tribe Eleutherodactylini) leptodactylid. No subfamilies are recognized.

Physical characteristics

These small toad-like anurans reach a maximum snoutvent length of 0.8 in (20 mm). The head is short, and the body is robust. The limbs are short to moderately long. The digits are reduced, so there are only two or three functional fingers and three or four functional toes. The dorsum is orange to greenish yellow or brown. The two halves of the pectoral girdle overlap midventrally (arciferal condition) and are fully ossified; a sternum is absent. Teeth are absent on the maxillaries and premaxillaries. The phalanges are short and reduced in number; the terminal phalanges are T-shaped. In Brachycephalus ephippium, a dermal bony shield ossifies dorsal to the vertebral column.

Distribution

All members of the family have restricted distributions in the coastal mountains to elevations of approximately 2,240 ft (750 m) from Espírito Santo southward to Paraná in eastern Brazil.

Habitat

Terrestrial amidst leaf litter on the forest floor.

Behavior

During the rainy season, brachycephalids are active by day and slowly walk about on the leaf litter. Males are territorial and advertise vocally and visually; male-male encounters have been observed. During the dry season, the toadlets seek shelter beneath leaf litter or under logs.

Feeding ecology and diet

Small arthropods, principally springtails and mites.

Reproductive biology

The advertisement call is a long, low-pitched buzz in Brachycephalus. Males grasp females around the waist (inguinal amplexus). Relatively large, unpigmented eggs are deposited terrestrially and undergo direct development into miniatures of the adults. Brachycephalus ephippium deposits up to five eggs per clutch but clutches of B. didactyla consist of a single egg.

Conservation status

Although not officially listed as threatened, these toadlets are restricted to the Atlantic coastal forest, much of which has been cleared.

Significance to humans

The skin secretions of Brachycephalus ephippium contain extremely strong toxins, tetradotoxin, and analogues.

Species accounts

List of Species

Pumpkin toadlet

Brachycephalus ephippium

taxonomy

Bufo ephippium Spix, 1824, Ilhéus, Bahia, Brazil (probably erroneous).

other common names

English: Spix's saddleback toad; Portuguese: Botão de ouro, sapinho dourado.

physical characteristics

This robust, short-legged toadlet is bright yellow to orange; the iris is black. Adults attain a snout-vent length of 0.5–0.8 in (12.5–19.7 mm). A bony shield ossifies dorsal to the vertebral column.

distribution

Serra do Mar and Serra da Mantiqueira in southeastern Brazil.

habitat

Terrestrial on and amid leaf litter on the forest floor in the Atlantic coastal forest.

behavior

Individuals actively walk slowly on the leaf litter by day during the rainy season. When the relative humidity approaches 100%, the toadlets often ascend low perches. Pumpkin toadlets commonly clean themselves by wiping the head and body with their limbs. During the rainy season, males are territorial and advertise their presence vocally. On approach by an intruder, the male toadlet moves an arm up and down in front of its eye. This movement may be derived from the wiping behavior. If an intruder does not retreat, a resident male may embrace or push the intruder until it departs.

feeding ecology and diet

Toadlets actively forage on the leaf litter and consume a variety of small arthropods, of which collembolans make up 54% of the diet, mites, 8%; and insect larvae, 6%.

reproductive biology

Reproductive activity occurs throughout most of the rainy season. Males call while in a high posture allowing for expansion of the large subgular vocal sac. The call consists of a continuous series of buzzes lasting two to six minutes with emphasized frequencies at 3.4–5.3 kHz. The first notes in the series are shortest with five or six pulses. Succeeding notes increase in length to as many as 15 pulses, but most of the notes have 10 pulses and a nearly constant pitch. Initial amplexus is inguinal as the male walks behind the female as she selects an oviposition

site in the leaf litter or under a log. Before oviposition the male moves forward and grasps the female nearly in an axillary position. This shift in position results in juxtaposition of the vents of both toadlets, maximizing fertilization. During a period of approximately 30 minutes, five large (0.2 in [5.1–5.3 mm] diameter), yellowish white eggs are deposited. The male leaves the site, but the female uses her hind feet to press and roll the eggs in the soil, particles of which adhere to the eggs and camouflage them. Then the eggs remain unattended. Embryos have a large yolk sac. The mouth is differentiated at 25 days of age, and a small tail is evident. By 41 days, fingers and toes are fully formed, and two egg teeth are present on the snout. By 54 days the tail is reduced in size, only one egg tooth is present, and the body is pigmented. Hatching occurs in 64 days. The miniature reddish brown toadlets retain a vestigial tail but no egg tooth.

conservation status

Not threatened. It exists within various protected areas in the Atlantic coastal forest.

significance to humans

Dermal glands secrete extremely strong toxins, tetradotoxin and analogues, which have biomedical importance.

Southern three-toed toadlet

Brachycephalus pernix

taxonomy

Brachycephalus pernix Pombal, Wistuba, and Bornschein, 1998, Morro do Anhagava, Serra da Baitaca, Paraná, Brazil.

other common names

None known.

physical characteristics

This robust, short-legged toadlet has a bright orange body, but the flanks, vent region, limbs, and area around the eye are black. Adults attain a snout-vent length of 0.5–0.6 in (12.0–15.8 mm). Ossified warts and a dermal shield are absent.

distribution

Southern part of the Serra do Mar, Paraná, Brazil.

habitat

Leaf litter in humid forest.

behavior

Diurnal; visual and vocal communication similar to that of B. ephippium.

feeding ecology and diet

These toadlets feed on small arthropods in the leaf litter by day; mites and insect larvae are the most common prey.

reproductive biology

The advertisement call is a low buzz. Reproductive activity occurs throughout the rainy season. Terrestrial eggs undergo direct development into miniature toadlets.

conservation status

Not threatened.

significance to humans

None known.

Resources

Periodicals

Pires Jr., O. R., A. Sebben, E. F. Schwartz, S. W. R. Larguna. C. Bloch Jr., R. A. V. Morales, and C. A. Schwartz. "Occurrence of Tetradotoxin and Its Analogues in the Brazilian Frog Brachycephalus ephippium (Anura: Brachycephalidae)." Toxicon 40 (2002): 761–766.

Pombal Jr., J. P. "Oviposition and Development of the Pumpkin Toadlet, Brachycephalus ephppium (Anura: Brachycephalidae)." Reuta Bras. Zool. 16 (1999): 967–976.

——. "A New Species of Brachycephalus (Anura: Brachycephalidae) from Atlantic Rain Forest of Southeastern Brazil." Amphibia-Reptilia 22 (2001): 179–185.

Pombal Jr., J. P., I. Sazima, and C. F. B. Haddad. "Breeding Behavior of the Pumpkin Toadlet, Brachycephalus ephippium (Brachycephalidae)." Journal of Herpetology 28 (1994): 516–519.

Pombal Jr., J. P., E. M. Wistuba, and M. Bornschein. "A new species of Brachycephalid (Anura) from the Atlantic rainforest of Brazil." Journal of Herpetology 32 (1998): 70–74.

José P. Pombal, Jr, PhD