Description
Atelopus nocturnus is a moderate-sized harlequin frog. The snout-vent length of adult females is 33.0 - 34.3 mm while the snout-vent length for adult males is 20.2 - 25.0 mm. The head of A. nocturnus is longer than it is wide, and the snout tapers to a point in dorsal view. In lateral view, the snout clearly protrudes beyond the lower jaw and curves from the tip of snout to the anterior margin of the lower jaw. The slightly protuberant nostrils are directed laterally and located posterior to the apex of the lower jaw. The canthus rostralis is present and the loreal region is concave. The interorbital region is flat and smooth, and the postorbital crest is visible. While the tympanum and tympanic annulus are absent, the tympanic areas are covered in warts. The temporal area is smooth and the widely-separated choanae are small and elliptical in shape. The skin of the lateral postocular region contains warts with pointed projections. The dorsum is smooth with scattered warts and noticeable vertebral neural processes. The warts increase in number towards the anterior and proximal upper surfaces of the forelimbs. The skin is smooth and wart-free on the throat, chest, stomach, and undersides of the hind limbs. The cloaca is directed posteriorly above the thighs with warts appearing lateral to the opening. The forearms are relatively short with tubercles on the undersides. The thumb of this species is short and all finger tips have round pads. The hands are webbed basally, with fingers lacking lateral fringes. The tibia, like the forearm, is relatively short. The feet are more extensively webbed than the hands, with the digits again having distinct pads (Bravo-Valencia and Rivera-Correa 2011).

DIAGNOSIS:

Atelopus nocturnus can be differentiated from similar Atelopus species by its moderate size, short hind limbs, pointed snout that protrudes beyond the lower jaw, absent tympanum and tympanic annulus, scattered warts on the dorsum, white pointed projections on warts of the arms and postocular region, apparent postorbital crest and vertebral neural processes, skin coloration, and bright yellow irises with black and brown spots (Bravo-Valencia and Rivera-Correa 2011).

COLORATION:

In life, female A. nocturnus have a dark reddish brown dorsum, with flank color transitioning from brown to orange. Males are dark brown on the dorsum and flank surfaces. The ventral surface of the body and limbs is bright orange in females, while males are white to yellowish cream-colored with irregular stripes and blotches of dark brown. The palmer hand and plantar in all individuals are orange, but with darker coloring in females. Both sexes have fingers I and toes I and II that are pale yellow, as well as bright yellow irises with brown spots and fine black reticulation. When preserved, the reddish hue of the female dorsum is lost and becomes dark brown. Any orange color, including on the ventral surface and flanks of the body in females and on the hands and feet in both sexes, turns cream in preservative along with the dorsal surfaces of fingers I and toes I and II. The white pointed projections on warts and outer metatarsal tubercle also turn cream in preservative (Bravo-Valencia and Rivera-Correa 2011).

VARIATION:

In addition to coloration, A. nocturnus exhibits sexual dimorphism in size as females are larger than males. Furthermore, the forearm is swollen and nuptial pads cover the dorsum of finger I in males. There is variation in the density of the warts on the dorsum flanks, and postocular region in females. In two male paratopotypes, the tops of the snouts are angled anteroventrally in lateral view (Bravo-Valencia and Rivera-Correa 2011).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Colombia

View distribution map in BerkeleyMapper.

Atelopus nocturnus is only found on the mainland of Colombia in South America, specifically in the northern Cordillera Central, Municipio de Anorí, Departamento de Antioquia, Colombia (Bravo-Valencia and Rivera-Correa 2011). Atelopus nocturnus lives in forest and inland wetlands, where it is very humid. The forest that it has been found in are subtropical and tropical moist montane and the wetlands are permanent rivers, streams and creeks (IUCN SSC Amphibian Specialist Group 2017). Their habitat is known to have lots of bromeliads, arboreal ferns and epiphytes. The species is found 1,670 meters above sea level (Bravo-Valencia and Rivera-Correa 2011).

Life History, Abundance, Activity, and Special Behaviors
Atelopus nocturnus is a nocturnal species that can be found in vegetation one meter off the ground near streams (Bravo-Valencia and Rivera-Correa 2011).

It is likely that A. nocturnus breed in the dry season as females were found with small white ova and males had nuptial excrescences during that season. They have axillary amplexus (Bravo-Valencia and Rivera-Correa 2011).

The reproductive behavior and larvae development is unknown, but other species in the genus Atelopus are observed to lay white eggs in strings underneath rock in shallow water (Starrett 1967).

The nutrition and predation of A. nocturnus is unknown as well, but other species in the same genus have been observed to feed on small arthropods such as ants and beetles (Crump 1988).

Trends and Threats
Atelopus nocturnus is listed as “Critically Endangered” on the IUCN Red List, and it occurs in two contiguous protected areas: Reserva Natural de las Aves Arrierito and Reserva la Forzosa. Anthropogenic activities, such as habitat loss, do not pose a threat. However, the species is rare, only a dozen individuals have been found despite exhaustive searches spanning over a decade (IUCN SSC Amphibian Specialist Group 2017). A possible threat to this species is Batrachochytrium dendrobatidis, which causes chytridiomycosis in amphibians, however further research is needed to assess this threat (Bravo-Valencia and Rivera-Correa 2011).

Possible reasons for amphibian decline

Disease

Comments

Phylogenetic Relationships:

ETYMOLOGY:

The species epithet is a reference to the nocturnal activity of A. nocturnus, from the Latin adjective “nocturnus.” At the time of its description, it was the only known nocturnal species in the genus Atelopus (Bravo-Valencia and Rivera-Correa 2011).

References

Bravo-Valencia, L., Rivera-Correa, M. (2011). “A new species of harlequin frog (Bufonidae: Atelopus) with an unusual behavior from Andes of Colombia.” Zootaxa, 3045, 57–67. [link]

Crump, M.L. (1988). ''Aggression in Harlequin Frogs: male-male competition and a possible conflict of interest between the sexes.'' Animal Behaviour, 36(4), 1064-1077.

IUCN SSC Amphibian Specialist Group. (2017). "Atelopus nocturnus". The IUCN Red List of Threatened Species 2017: e.T21567292A21567295. https://dx.doi.org/10.2305/IUCN.UK.2017-3.RLTS.T21567292A21567295.en. Downloaded on 19 February 2021.

Starrett, P. (1967). ''Observations on the life history of frogs of the family Atelopodidae.'' Herpetologica, 23(3), 195-204.

Species Account Citation: AmphibiaWeb 2021 Atelopus nocturnus: Nocturnal Harlequin Toad <https://amphibiaweb.org/species/7725> 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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