Description
Silverstoneia dalyi is a small nurse-frog with an adult male snout-vent length range between 14.9 - 17.9 mm and an adult female range between 15.7 - 19.0 mm. When viewed dorsally, the snout ranges from blunt to sharply rounded. The posterodorsally directed nostrils are somewhat flared, and the canthus rostralis is rounded. The loreal region is flat or weakly concave and is typically vertical but may have a slight outward slope. The pupils are horizontal. The tympanum is about 33% - 48% of the eye length and directed posterodorsally. An incomplete tympanic ring is present on the lower half of tympanum, but there is no supratypmanic bulge (Grant and Myers 2013).

The length of the hands is between 19 and 23% of snout-vent length and between 83 and 100% of the length of the forearm. There is no metacarpal fold. The hands possess a weak, elliptical thenar tubercle and a weak, elliptical to bluntly triangular palmar tublercle. The fingers are fringeless and have a typical relative finger length of III > I > II > IV, however, finger IV can range from being much shorter and stubbier than finger II to about the same length. Additionally, fingers II and IV range in their relative length with finger III with them reaching anywhere between the proximal subarticular tubercles to the distal subarticular tubercles. Fingers I and II each have a single, protuberant subarticular tubercule, fingers III and IV have two each with the distal subarticular tubercles being inconspicuous. Adult males’ third finger is swollen on the preaxial surface. The swelling extends to level of the distal subarticular tubercle of finger III (Grant and Myers 2013).

The length of tibia ranges between 40 and 60% of snout-vent length. The foot length is between 33 and 42% of snout-vent length and has a weak metatarsal fold that extends almost to the outer metatarsal tubercle. The well-defined tarsal keel is tubercle-like, and strongly curved. The keel is approximately a third of the length from the inner metatarsal tubercle. The relative toe lengths are IV > III > V > II > I. Toes I and II have one subarticular tubercule, toes III and IV have two, and toe V has three. There is basal webbing between toes III and IV with a webbing formula of III e – (4 – 4 1/2 ) IV. There is occasionally rudimentary webbing between toes II and III. The toes are fringeless (Grant and Myers 2013).

The skin of the dorsal and ventral surfaces is smooth in preservative; in life, the posterior dorsum is granular. The skin on the exposed surfaces of the lower leg is slightly granulated in preservative, but conspicuously granular in life (Grant and Myers 2013).

Tadpoles are slender and have a total length between 9.8 and 11.2 mm at stage 24. The head-body length ranges from 3.1 – 3.6 mm. The head-body is slightly depressed and ventrally flattened. In the dorsal view, the snout is rounded and in the profile it slopes anteriorly. The eyes are dorsolateral. The nares are directed laterally and positioned dorsally, closer to the snout than the eyes. The vent tube is attached to the ventral fin and likely opens dextrally. The tail fins originate close behind body and are low; at their highest point they are about as high as the body. The dorsal and ventral fins are equal in height at the midtail. The tip of tail is slightly rounded to pointed with undeveloped tail musculature at the tip. The notochord is still visible at the end of the tail. The puckered ventral mouthparts of larvae include an umbelliform oral disc with smooth edges and no tooth rows. The oral disc has a shallow median notch on the posterior edge that is often hidden by the convoluted folding on the lower labium. Pappillae are present on posterior labium with a single oblong papillae at the midline. The jaw sheath is unkaratinized, but has minutely serrated sharp points on the edge (Grant and Myers 2013).

At stage 44, one individual had a totally body length of 21 mm and a head-body length of 8.5 mm. At stage 46, one individual had a snout-vent length of 10.5 mm (Grant and Myers 2013).

Silverstoneia dalyi can be differentiated from all other Silverstoneia species except S. gutturalis by the dark brown spot behind the corner of the mouth found in most individuals, which extends ventrally to the throat. Silverstoneia dalyi can be distinguished from S. gutturalis by the former having a smaller snout-vent length, by the lack of elongated spots on the throat, and by the presence of the dark brown, elongated spots or stripe found on the inner surface of the tibia. Additionally, S. gutturalis has a different range than S. dalyi, occurring farther north in Serrania del Baudo (Grant and Myers 2013).

In life, coloration varies some by locality. The dorsum is brown at the type locality in Quebrada Docordó and grayish brown at Playa de Oro. The black flanks have an oblique lateral stripe that runs from the groin, where it starts as various shades of orange, to the eye, where it is bronzy tan in color. There is an axillary flash mark. A ventrolateral stripe runs the length of the body from the lip and extends anteriorly over the shoulder. Its color starts as bronzy white or tan at the lip and becomes white or bronzy white as it moves posteriorly. The limbs are dull transparent orange, revealing orange-colored muscle beneath the skin. The thighs are a slightly brighter orange. The inner surface of the tibial segment of the leg has dark brown, elongated spots or a stripe that connects to the groin. The ventral surface is white to grey. There is a diagnostic a dark brown spot behind the corner of the mouth in most specimens (Grant and Myers 2013).

In preservative, the dorsum, head, and snout become pale to very dark brown. The eyelid is blackish and the head has a blackish brown facemask that connects posteriorly to the flank. Below the facemask, the head is creamy white with differing concentrations of melanophores that ranged from a faint stippling to a blackish brown upper lip stripe. When present, the lip stripe is isolated to the lips and separated from the mask by a white space. The dark spot at the corner of the mouth ranges in size from a small dot to large blotch that extended to the throat. The dorsum is patterned with randomly scattered lighter and darker blotches. Individuals sometimes have a black vertebral stripe from the underlying vertebral column, not from skin pigmentation. The axilla and surrounding area are free of melanophores. The flanks are blackish brown with an oblique lateral strip that divided the flank, connecting the eye to the groin with coloration that starts as creamy white near the eye and becomes infused with melanophores as it moves posteriorly. In some specimens the stripe continues to the snout. The throat, chest, and belly typically do not have patterning, however the throat can have a diffuse wash of melanophores in the middle. A pale ventrolateral strip is present and lined with diffuse stippling or poorly defined spots (Grant and Myers 2013).

The dorsal surface of the arm is light brown with a randomly scattering of dark brown blotches. The anterior and posterior surfaces of the upper arm have dark brown longitudinal stripes that are well defined and broad. The stripe on the posterior surface wraps around the outer, ventral surface of the elbow and onto the palmar side of the hand. The hand, otherwise, has creamy white spots. The contact surfaces of the tubercles are gray. There is no light strip connecting the palmar tubercle to the base of finger IV (Grant and Myers 2013).

The dorsal surface of the thighs is light brown and the longitudinal stripe on anterior surface becomes blackish brown, connecting with the dark flank. The ventral surface of the thigh does not have patterning. The posterior surface of the thigh is blackish brown with a white stripe. The blackish brown coloration continues down to the concealed surface of the shank where it becomes a broken stripe, solid strip, or a series of elongated spots. The exposed surface of the shank and foot have diffused dark brown blotches. The concealed surfaces of the foot are creamy white and lack melanophores. The ventral surface of the foot is brown and the contact surfaces of the tubercles are grey. In specimens with metatarsal keels, the keel is creamy white; in specimens without keels, the area is still white. The toe webbing is white and free of melanophores (Grant and Myers 2013).

In preservative, the head-body and tail of tadpoles is pale brown, with reflective silver iridophores scattered over the head-body and less densely over the tail. The fins are transparent but also have a few silver iridophores. One specimen had an orange-brown tail tip. In life, the iridophores were also visible (Grant and Myers 2013).

At stage 44, an individual tadpole had a pale oblique lateral line and the throat and chest had a light scattering of melanophores. At stage 46, another tadpole had well-developed adult color patterns. For both individuals, the postrictal (mouth spot) was missing but small iridophores were still present (Grant and Myers 2013).

Silverstoneia dalyi can vary in both morphology and patterning. The snout can be bluntly or sharply rounded. The dark postrictal spot is not found in all specimens. The lateral stripe in some specimens is yellow near the groin (Grant and Myers 2013).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Colombia

View distribution map in BerkeleyMapper.

Silverstoneia dalyi inhabits low elevation rainforests and swamp forests, between 100 and 210 m, along streams in the Rio San Juan drainage, Chocó Department on the Pacific side of Columbia (Grant and Myers 2013). It is only known from three to five threatened sites in an area measuring 3,379 km² (IUCN 2017).

Life History, Abundance, Activity, and Special Behaviors
Silverstoneia dalyi is a terrestrial, freshwater, diurnal species (IUCN 2017).

Silverstoneia dalyi has an advertisement call that has been described as cricket-like chirping (Grant and Myers 2013).

Eggs are laid on the ground. However, males are nurse frogs, carrying tadpoles on their backs to transport them to streams where development is completed (IUCN 2017). Up to six larvae being carried at a time has been observed (Grant and Myers 2013).

Trends and Threats
Silverstoneia dalyi is listed by the IUCN Red List as “Endangered” due to habitat loss, mining, illegal agriculture, and illegal logging. Although the species is locally a common species, it is not found in any protected areas and is threatened by loss of habitat and habitat quality. Additionally, little is known about the species distribution, population status, or ecology. The species population is assumed to be decreasing (IUCN 2017).

Possible reasons for amphibian decline

General habitat alteration and loss
Habitat modification from deforestation, or logging related activities
Intensified agriculture or grazing
Habitat fragmentation

Comments
The species authority is: Grant, T., Myers, C. W. (2013). “Review of the frog genus Silverstoneia, with descriptions of five new species from the Colombian Chocó (Dendrobatidae: Colostethinae).” American Museum Novitates 3784 1-58.

The genus Silverstoneia is named after Dr. Philip Silverstone and the species epithet, dalyi, is named after Dr. John William Daly. Both were scientists who studied dendrobatid frogs (Grant and Myers 2013).

Silverstoneia dalyi appears to be limited to the Rio San Juan drainage, other frogs in the area have a distribution that is independent of river basins. More investigation is necessary to determine if S. dalyi is truly has a restricted range and why (Grant and Myers 2013).

Silverstoneia dalyi may be the species Dunn referenced as Phyllobates floator from Río San Juan in his 1957 article (Grant and Myers 2013).

References

Grant, T., Myers, C. W. (2013). ''Review of the frog genus Silverstoneia, with descriptions of five new species from the Colombian Chocó (Dendrobatidae: Colostethinae).'' American Museum Noviates, 3784, 1-58.

IUCN SSC Amphibian Specialist Group. 2017. Silverstoneia dalyi. The IUCN Red List of Threatened Species 2017: e.T78586259A85891981. Downloaded on 31 May 2018.

Species Account Citation: AmphibiaWeb 2018 Silverstoneia dalyi <https://amphibiaweb.org/species/8084> 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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