Atelopus sorianoi La Marca 1983

Compared to other species within the Atelopus genus, Atelopus sorianoi is relatively large; males have a snout-vent length range of 38.2 - 39.8 mm and females have a snout-vent range of 42.2 - 49.1 mm. The dorsal view of the species’ snout is somewhat sharp, but rounded at the tip and in the lateral view it is acutely pointed. The snout extended beyond its lower jaw. Its rounded nostrils are closer to the end of snout and directed laterally and slightly posteriorly. There is a distinct depression between the nostrils. The canthus rostralis is sharp with a thick ridge. The loreal region is vertical. The eye is larger than the distance between the eye and the nostril. The eyes bulge laterally out of the head with eyelids thicker along the outer border. The tympanum and tympanic annulus are absent in the species. Atelopus sorianoi have well-developed supratympanic crest, but have no vocal sacs or slits in males. The head is about as wide as it is long and can be narrower than the body (La Marca 1983). The body and legs are not elongated. At the posterior end of the body, outlines of their extended sacral diapophyses, spines of the vertebrae, and urostyle are visible through the skin. Fingers of the species have simple and slight webbing, no fringes, rounded tips and pads, and a distinctly thick first finger. Relative finger lengths are 3 > 4 > 2 > 1. The subarticular tubercles are oval and low. There is a single rounded inner metacarpal tubercle. Relative lengths for toes are 4 > 5 > 3 > 2 > 1 and the tips are rounded. The subarticular tubercles of the toes are single, inconspicuous, flat, and elongated, as is the inner metatarsal tubercle. The outer metatarsal tubercle is smaller than the inner, but rounder and elevated. Using the S/H webbing system, the webbing formula for the toes is I1- - 2+II2 - 2-III2 - 3+IV3+ - 2-V. When the hindlimb is adpressed the heel reaches the temporal region. There is no tarsal fold. The tibia length is 37.1% of the snout-vent length. The anal opening is directed straight back, protruded, and located just above the mid-thigh line (La Marca 1983).Skin on the head is smooth, but the temporal region is speculated. The lower dorsal part of its body has a few warts. Two ridges of warts can be seen on the dorsolateral portion starting from the squamosals to the inguinal region. The upper dorsum is smooth and lower dorsum finely granular with some shallow tubercles on the sacral region. The ventral side ranges from smooth to finely granular. The throat is the smoothest region of the body. The extremities have a more granular texture than the body with the ventral side being smoother than the dorsal. The flanks have larger tubercles and the groin has wrinkles (La Marca 1983). Tadpoles have one spiracle that opens on the left side of the slightly flattened body. They eyes are relatively large and the nostrils are situated closer to the eyes than they are to the end of the nose. The larvae have a row of small papillae on the upper part of the mouth, as well as keratinous mouthparts. Tadpoles of this genus are typically quite small, averaging out to be less than 22 mm in length (Duellman and Lynch 1969, Mijares-Urrutia and La Marca 2005).At the time of discovery only four previously known Atelopus (A. carbonerensis, A. crucigerum crucigerum – now known as A. cruciger, A. mucubajiensis, and A. oxyrhynchus) were known from Venezuela. Atelopus sorianoi is differentiated from those species based on their unique coloration (see coloration below); this species has no distinctive markings on its body or face. Atelopus sorianoi was most similar to A. carbonerensis but could be differentiate by A. carbonerensis having a curved canthus rostralis, nostrils that are less elevated, a different webbing formula, yellow dorsal coloration with brown markings, and a larger male snout-vent range of 40.3 – 46.0 mm. From A. cruciger, it can be differentiated by A. cruciger having a yellow or green dorsum with brown markings, an eye diameter that is equal to the distance between the eye and the nostril, and an adpressed hindlimb that reaches the eye. From A. mucubajiensis, it can be differentiated by A. mucubajiensis having a smaller snout-vent length, yellow dorsal coloring with brown markings, having a more acute snout, and an eye diameter equal to the distance between the eye and nostril. From A. oxyrhynchus, it could be differentiated by A. oxyrhynchus having a yellow-brown dorsum with brown markings and bands on the canthus and supratymanic regions, more tuberculated skin, and a curved canthus rostralis (La Marca 1983). In life, the body is orange-red throughout with no markings. It does not have any green or dark colors around the nasal passage. In preservative, the body is a creamy or uniformly yellow in color (La Marca 1983). The color of larvae is dark brown mixed with black, and alongside the species tail there are little spots and white bands (Mijares-Urrutia and La Marca 2005).Females are typically larger than males in body size. The supratympanic crest is more obvious in males than females. Females have long and slender forelimbs while males have short and stocky forelimbs and more granular surface on all limbs. Males have keratinized pads on some of their fingers that may extend to the base of the second finger. Males usually have heads as wide as their body with more acute snouts; females have heads narrower than the body. When fore and hindlimbs are adpressed the elbow and knee touch in males but do not in females (La Marca 1983).The species authority is: La Marca, Enrique. (1983). A New Frog of the Genus Atelopus (Anura: Bufonidae) From a Venezuelan Cloud Forest. Contributions in Biology and Geology 54, 1-11.Atelopus oxyrhynchus and Atelopus carbonerensis seem like the closest relative to the Atelopus sorianoi. It is possible that all three species were derived from an ancestral group within the cloud forests where they are distributed. Yet, there is no known synapomorphy that unites them. Independent speciation events could have been possible due to the local distribution of the Atelopus genus and differences in habitat needs. Speciation may have also been due to isolation and adaptive responses to the environment (La Marca 1983). Atelopus sorianoi may have evolved in isolation and adapted to a particularly humid environment (La Marca 1983).In the 1970s, a mammalogist named Pascual Soriano found and photographed an Atelopus specimen that was different from all then-known species of Venezuelan Atelopus based on its coloration and location. It was rediscovered at the exact stream visited by Soriano and thus it was named after the discoverer (La Marca 1983).

This photophilic species inhabits an area of the forest within the Paramito de San Francisco, in Merida State, Cordillera de Merida, in the Bolivarian Republic of Venezuela and is associated with a lone stream within an isolated cloud forest. The isolated cloud forest has humid conditions with montane vegetation above the continuous timberline. Its habitat is isolated because of the lowlands of the Chama River valley, specifically the deep xerophytic valleys found around the region. Atelopus sorianoi has the most restricted range of any species in the family and lives only at an altitude of 2,400 to 2,700 meters (La Marca et al. 2005, La Marca et al. 2010).

All specimens included in the original description were found at mid-day in undisturbed cloud forests, on the ground near the cascading stream (La Marca 1983).

Atelopus sorianoi populations have been found to be severely declining. In a recent study, scientists found that ninety percent of Atelopus species populations in Venezuela are severely declining. The species has possibly become extinct. It has not been found in the Paramito de San Francisco since 1990 (La Marca et al. 2005).The species is highly at risk for a severe disease. Batrachochytrium dendrobatidis might be the explanation for the major declines of Atelopus toads (La Marca et al. 2005, Lampo et al. 2006).Another major cause of population declines has been climate change. A severe drought was experienced in the region where the frogs exist at the same time as the chytridiomycosis outbreaks. This could have exacerbated the effects of the disease epidemic and caused many more deaths of the toads (Lampo et al. 2006, La Marca and Soriano 2005). Lastly, the International Union on the Conservation of Nature stated that clear cutting has caused a reduction in habitat for the scarlet harlequin toad. This loss of habitat could be another reason the population is dwindling (La Marca et al. 2010).

The scarlet harlequin toad or sapito arlequin de Soriano (Atelopus sorianoi) is a species of toad in the family Bufonidae. It is endemic to Venezuela. Its natural habitats are subtropical or tropical moist montane forests and rivers. It is threatened by habitat loss. It may already be extinct. The toad is among the 25 “most wanted lost” species that are the focus of Global Wildlife Conservation's “Search for Lost Species” initiative.