Elegant stubfoot toad
© 2010 Andrés Acosta (1 of 3)
The forelimb is slender and long. When the forearm is adpressed posteriorly along the body, the palm reaches the vent. The palms have deep, fleshy folds and low, rounded tubercles. The hands have full, fleshy webbing that almost obscure the first finger and is deeply incised between the second, third, and fourth fingers. The fourth finger is considerably longer than the second and reaches beyond the penultimate joint of the third (Peters 1973).
The hind limb is also long and slender. When adpressed anteriorly along the body, the tibiotarsal articulation reaches the area between the loreal region and the posterior margin of the eye. When the hind limbs are held at right angles to the body, the heels overlap. The foot is fleshy with deep grooves or folds. The planter tubercles are weak and indistinct; the outer metatarsal tubercle is poorly defined, and the inner is nearly indistinguishable. The webbing on the foot is also thick and fleshy. The first and second digits are enclosed, except for their tips. The rest of the toes are fully webbed with shallow incisions. Along the fourth toe the webbing extends to the tip as a fringe. The fifth toe is longer than the third. There are no distinct subarticular tubercles (Peters 1973).
At Gosner stage 25, A. elegans larvae have a total length range of 6.2 – 6.7 mm, with a body length range of 2.6 – 2.8 mm. The body has an average width of 1.8 mm, is oval from a dorsal and lateral views, and is flattened ventrally. The snout is round, both from the dorsal view and in the profile. There is noticeable constriction of the body at the eyes and at the spiracle. Circular nostrils with incomplete rims are present about half the distance from the tip of the snout to the eyes and located dorsolaterally. The internarial distance is slightly smaller than the interorbital distance. The dorsal eyes are directed dorsolaterally and the space between them is twice the eye diameter. The spiracle is sinistral and located almost two-thirds of the body length posteriorly from the snout. The spiracle has a dorsally directed free tube with the diameter of the opening being equal to the tube length. The vent tube does not protrude from the end of the body. The tail length range is 3.6 – 3.9 mm or about 58% of the total length. The caudal musculature is robust at the base but begins to evenly narrow after one-third the distance from the body. The tail is generally rounded with a dorsal tail fin that begins at the level of the body and is 40% of the tail height. The ventral fin begins just posterior to the vent tube. The ventral mouth has surrounding labia that form a complete oral disc with a width of 1.8 mm. Larvae have 37 marginal papillae arranged in uniserial rows on the dorsal and ventral region. The ventral region has a gap on the most posterior portion of the lip. No submarginal papillae are present at stage 25 but they become visible in later stages. The labial tooth formula is 2/3 with complete rows of anterior and posterior teeth that are equal in length. The jaw sheaths are also equal in length and have serrated inner margins. The upper beak is somewhat concave and the lower is V-shaped. Larvae possess both long and short-cusped teeth as well as teeth with no cusps. Posterior to the mouth there is an abdominal sucker that is 44% of the total length. The distinguishable abdominal sucker is composed of a stripe of large, protruding cells. By stage 43, when the tail fin height has also decreased, the abdominal sucker is no longer present (Marcillo-Lara et al. 2020).
Atelopus longirostris and A. balios are the most similar species within A. elegans’ range. Atelopus longirostris displays a tan dorsal color with yellow markings and a white ventral coloration, which differs from that of A. elegans. Atelopus longirostris can also be distinguished from A. elegans by the prominent extension protruding from the snout that is absent in A. elegans. Atelopus balios is similar to A. elegans in coloration, however, where A. elegans has interdigital webbing that almost entirely covers the thumb, A. balios has a free and visible thumb that protrudes from the webbing membrane (Ron et al. 2018).
Unique larval color patterning of tan with brown, yellow, and black markings distinguishes larval specimens of A.elegans from larvae of other species within the Atelopus genus. The presence of short-cusped teeth in A. elegans also differentiate it from the A. palmatus, which have stronger, long-cusped teeth (Marcillo-Lara et al. 2020).
In life, adult A. elegans ranges in color from brilliant yellow to a dark olive green. Clearly defined black spots are always present on the back and limbs. The ventrum of A. elegans is yellow, with orange on the bottoms of the feet and toes. Atelopus elegans has a black eye with a light-yellow ring around the pupil (Ron et al. 2018). A black stripe is present beginning at the tip of the snout and continuing through the eye along the full extent of both sides of the body to the groin (Boulenger 1882).
In preservative, the dorsal ground color of adults is white with a pattern of black or brownish parallel stripes that begin posterior to the eyelid and are joined by bars as it extends to the cloaca. The dorsal strips are connected by vermiculations or lateral bars at irregular intervals or separated by additional lengthwise stripes or by light spots with brown borders or by brown spots with white borders. In most individuals, there is a solid white line that runs from the eye to the groin along the dorsolateral line. Below the white line is a dark bar that begins at the snout, crosses the canthus laterally, through the eye, and continues to the groin. There is no pigment on the lateral or ventral surfaces below this dark line. The dorsal surfaces of the limbs and feet have dark brown to black mottling, streaks, and strips, similar to the body. The ventral surfaces of the limbs are uniformly yellowish white (Peters 1973).
In life, A. elegans larvae have unique coloration patterns that can be used to distinguish them from larvae of other species. The body of larval A. elegans is dark tan with brown and dark yellow spots and some black markings. The dark yellow spots can be found around the eyes and top of the snout, while no brown or black markings are found in this area. The black markings are always larger than the brown or mustard yellow spots. The tail is tan and has brown spots mostly on the dorsal surface while black marks can be found at the anterior part of the tail and the posterior margins of the tail musculature. The spiracle has some mustard spots at the base. The heart and some blood vessels can be seen ventrally, and the abdominal sucker and mouth are transparent. The lower abdomen is colored and patterned similarly to the dorsum. When preserved, the color and patterning largely remain the same but the mustard spots fade. The spiracle becomes unpigmented. While the abdominal sucker remains transparent, the ventrum becomes tan (Marcillo-Lara et al. 2020).
In life, metamorphs at stage 41 begin to develop golden dorsolateral strips that become more defined and turn cream colored at stage 43 (Marcillo-Lara et al. 2020).
Adult A. elegans exhibit sexual size dimorphism (Velalcázar Guerrero 2014). There are color differences between the Gorgona Island population and the Ecuadorian populations (Ron et al. 2018).
Between Gosner stages 30 - 35 larvae have visible submarginal papillae that are not present in lower stages (Marcillo-Lara et al. 2020).
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Colombia, Ecuador
A separate population is also found at sea level in the lowlands of Gorgona Island off the coast of Columbia. There is some dispute on whether to include the Gorgona Island population within this species or to consider it a separate species (Atelopus gracilis) or subspecies (Marcillo-Lara et al. 2020).
Life History, Abundance, Activity, and Special Behaviors
Mature adults have been found in open areas (paddocks) adjacent to forests, in secondary growth forests, flooded areas and in riverbank vegetation. At night, they have been known to perch on leaves in the canopy (IUCN 2019). An adult female was observed walking during the day along a stream. However, very little information is available on their use of micro-habitats (Coloma and Almeida-Reinoso 2012).
Very few population surveys have been conducted for A. elegans over the past 10 years, but the greatest abundance has been found on Gorgona Island, Colombia, which may be a different species, Atelopus gracilis. In 2012, at the Parque Nacional Natural (PNN) Gorgona, 123 individuals were observed during a distance sampling study for population density, and A. elegans was estimated to have a density of 0.01 individuals/m2 (Gomez-Hoyos et al. 2017).
Near Durango, Esmeraldas Province in Ecuador, eight individuals were found in 2009 by a field party from the Museum of Zoology of Ecuador (Ron et al. 2011). For a 2011 - 2012 study 20 adults were found along a riverbank in Durango, Province of Esmeraldas, Ecuador (Coloma and Almeida-Reinoso 2012).
In 2012, an ex situ breeding experiment was conducted using four males and 17 females. Only one female laid a clutch, and only after being stimulated by Human Chorionic Gonadotropin hormone. The clutch of eggs was laid the next day under a stone and produced 300 tadpoles (Coloma and Almeida-Reinoso 2012).
Larvae of A. elegans are gastromyzophorus, having an abdominal sucker, which is an ecomorphological trait used to keep their position in torrential fresh-water streams and rivers (Altig and Johnson 1989).
Trends and Threats
The major threats facing A. elegans are habitat loss and infection from the chytrid fungus Batrachochytrium dendrobatidis (Bd). In Ecuador, the forests where this species can be found are declining in quality and area due to agriculture, logging, mining and expanding human settlements. Throughout its Ecuadorian range, only 23.9 percent of the original vegetative cover remains undisturbed (IUCN 2019).
Occurrence of Bd in the Ecuador populations is uncertain, but samples from museum specimens detected evidence of infection dating back to at least 2000. Bd fungus has been found in individuals inhabiting Gorgona Island, off the coast of Columbia, since 2000 where the population suffered an initial decline related to the infection but has since recovered and remains stable although chytrid fungus is still present in many individuals. From 2007 to 2012, the Gorgona Island population did not show any declines and incidence of Bd infection decreased steadily (Flechas et al. 2015). The remaining population is characterized by a bacterial community present on the skin that shows resistance to the fungus, which may increase resilience. This population may also be less susceptible to Bd due to its low elevation habitat which is less favorable for Bd growth (Flechas et al. 2012). The impact of the Bd infection on the Ecuador population is unknown.
A range-wide population estimate is unknown and there are no current population monitoring systems in place. The last population survey to occur took place in 1994 in the province of Cotopaxi. The current assumed extent of occurrence is 4,287 square kilometers within two locations: Esmeraldas province in Ecuador and Gorgona Island off Columbia (IUCN 2019). Although serious declines have been reported in Ecuador, the Gorgona Island population appears to be abundant and remains stable after recovery following declines due to chytrid fungus (Gomez-Hoyos 2017).
Captive breeding was attempted in Ecuador during a 2011 - 2012 study as ex situ management for proactive conservation of A. elegans. A total of three males and seventeen females were collected from a riverbank in Durango, Province of Esmeraldas, Ecuador resulting in the first successful oviposition event in captivity for the species (Coloma and Almeida-Reinoso 2012).
Another captive colony of A. elegans has been studied under the Balsa de los Sapos initiative at the Pontifical Catholic University of Ecuador for conservation purposes (Ron et al. 2018).
Possible reasons for amphibian decline
General habitat alteration and loss
The genus Atelopus is a monophyletic group within the family Bufonidae. Atelopus has been demonstrated to be monophyletic through many studies, but the detailed interspecific, intraspecific, and intergeneric relationships within Atelopus are poorly understood. This is partially due to extreme morphological similarities between species, making collection and identification difficult. More so, nearly all of the more than 100 species within the genus Atelopus have suffered severe population decline and many species are now thought to be extinct, thus making collection and sample obtention difficult, if not impossible for many species (Lötters et. al. 2011).
The lowland Gorgona Island population was originally named as a separate species, Atelopus gracilis, by Thomas Barbour in 1905 because it is geographically separate and has a different coloration (Ron et al. 2018). More work is needed to determine this population’s placement.
The species epithet “elegans” is derivative of the Latin “elegans”, which translates to “elegant” or “handsome”, and was named as such in reference to the smooth and unblemished nature of the skin of this species (Ron et.al. 2018).
The species was originally described as Phryniscus elegans (Boulenger 1882), and other synonyms include Atelopus gracilis (Barbour 1905) and Atelopus varius elegans (Cochran and Goin 1970).
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Written by Jacquelynn Baca, Elizabeth Carroll, Ashley Grider (bacaj AT oregonstate.edu, carrmary AT oregonstate.edu, gridera AT oregonstate.edu), Oregon State University
First submitted 2020-10-27
Edited by Ann T. Chang (2020-10-27)
Species Account Citation: AmphibiaWeb 2020 Atelopus elegans: Elegant stubfoot toad <http://amphibiaweb.org/species/45> University of California, Berkeley, CA, USA. Accessed Dec 1, 2020.
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Citation: AmphibiaWeb. 2020. <http://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 1 Dec 2020.
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