Atelopus balios

Geographic Range

Atelopus balios commonly known as the Rio Pescado stubfoot toad, is an endemic species found in Ecuador, specifically in the Pacific Lowlands of South-western Ecuador. Historically, populations were concentrated in the Naranjal region, where they inhabit riparian zones and montane forests. However, due to habitat loss, climate change, and disease, their distribution has significantly declined. Conservation efforts, including ex-situ breeding programs, have focused on sustaining their dwindling populations. According to research, this species has only been found in four localities in the Province of Guayas, in Azuay, Canar, the San Miguel community, and the Naranjal Canton.

• Biogeographic Regions
• neotropical neotropical
  • native native

Habitat

Atelopus balios primarily inhabits moist, tropical forests and montane riverine ecosystems with high vegetative cover in Ecuador. It is a terrestrial species that depends on well-oxygenated, fast-flowing streams for reproduction. The species flourish in tropical humid, lowland rainforests that are 200-460 m above sea level. A. balios thrives in optimal temperatures of 22°C to 30°C throughout the year.

Tadpoles are highly specialized for their aquatic environment, utilizing suction-based adaptations to cling to submerged surfaces in fast-moving water. Adults also prefer mossy stones that serve as call sites for males all year-round and breeding sites where females return to during breeding season.

• Habitat Regions
• tropical tropical
• terrestrial terrestrial
• freshwater freshwater

• Terrestrial Biomes
• rainforest rainforest

• Aquatic Biomes
• rivers and streams

Physical Description

Atelopus balios is a small toad with smooth light green skin covered dorsally with small black spots and their under belly is a cream yellow. Their limbs are slende and long. The toes and fingers are partially webbed. Their soles, webbing, palms and perianal regions are bright orange in color. These vibrate color patterns likely serves as a warning to predators about its toxicity.

The tadpoles of Atelopus balios have unique buccopharyngeal structures that align with their ecological niche, allowing them to feed efficiently in their aquatic habitat. The buccal cavity includes a well developed oral disc with numerious labial teeth that aid in attachment to submerged surfaces. The pharyngeal region features a complex arrangement of papillae including postnarial, buccal floor and buccal roof papillae. This structure supports both feeding and respiration in a stream dwelling larval stage, enabling the tadpoles to filter fine organic particles while maintaining their position in flowing water.

The tadpoles also have a shorter and higher tail compared to most other Atelopus species. They have irregular yellowish-brown marks on the tail musculature. The adult males measure between 30-38 mm from snout to vent, while adult females range from 40-50 mm. They exhibit sexual dimorphism, with females being almost twice as large as the males.

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry
• poisonous poisonous

• Sexual Dimorphism
• female larger

Development

Female Atelopus balios lay their eggs in well oxygenated freshwater streams, attaching them to the underside of rocks. After laying, the hatching will occur within 11-14 days dependant on the temperatures. The tadpoles of this species take between 2 and 4 months to complete their metamorphosis. Atelopus balios tadpoles undergo a typical anuran metamorphic cycle, transitioning from eggs to tadpoles before reaching adulthood. Tadpoles have specialized mouthparts adapted to fast-flowing water environments, enabling them to adhere to rocks and feed on biofilms. The developmental stages have been extensively studied in ex-situ conditions, particularly in conservation breeding programs aimed at ensuring the species' survival.

• Development - Life Cycle
• metamorphosis metamorphosis

Reproduction

Their breeding season is from June to December. Atelopus balios follows an oviparous reproductive strategy, with external fertilization occurring in stream environments. Males engage in amplexus behavior, gripping females to facilitate fertilization. The axillary amplexus can last from 1-5 days. These amplectant pairs will stay submerged for 3-4 days before oviposition and stay underwater for approximately 2-3 hours. This frequency of immersion increases as the day of oviposition approaches, they become submerged the whole day even prior to oviposition. Due to lack of specific information on mating systems of Atelopus balios , their exact mating system is unknown. However, based on what is known about other Atelopus species, this species likely exhibit a promiscuous or polygynous mating system as well rather than strict monogamy.

During reproduction, amplectant pairs will seek submerged locations and display repeated immersion behavior. After amplexus is established, the female moves to a suitable site to lay her eggs. The male then releases sperm to fertilize the eggs externally. This reproductive behavior is influenced by environmental conditions. Observations from related species indicate that factors such as water temperature and humidity can significantly affect reproductive success and tadpole development. On an average they will lay upto 150-600 eggs and the tadpoles will hatch within 8-12 days.

• Key Reproductive Features
• gonochoric/gonochoristic/dioecious (sexes separate)
• fertilization fertilization
  • external external
• oviparous oviparous

Clutches can contain up to 150-600 unpigmented eggs, typically laid in strings under submerged stones, as observed in captive studies. However, there is no parental care provided by either the male or female following fertilization.

• Parental Investment
• no parental involvement

Lifespan/Longevity

The lifespan of A. balios in the wild is not well-documented due to population declines. However, individuals in captivity have been known to survive for several years under optimal conditions. A retrospective study on amphibian pathology cases suggests that individuals are susceptible to a range of diseases atop habitat destruction, particularly chytridiomycosis, a fungal pathogen called Batrachochytridium dendrobatidis , which has contributed to their decline.

Atelopus balios is most closely related to Atelopus varius , both belong to the same genus and share similar ecological and morphological traits. Therefore, it is likely that A. balios too has a similar lifespan of around 10 years in captivity.

Behavior

Atelopus balios is primarily diurnal, engaging in active foraging and mating behaviors during daylight hours. It is known for its slow, deliberate movements, a trait observed in many Atelopus species. The species exhibits site fidelity, often returning to specific breeding sites annually. However, its behavioral ecology remains poorly understood, particularly in natural habitats where observations are rare.

• Key Behaviors
• terricolous
• diurnal diurnal
• motile motile
• sedentary sedentary

Home Range

Although specific data on the home range of Atelopus balios is limited, existing observations indicate that the species inhabits regions characterized by dense vegetation and lowland valleys adjacent to streams in southwestern Ecuador. Given its equatorial distribution, A. balios likely experiences a consistent photoperiod of approximately 12 hours of daylight and 12 hours of darkness year-round. This equatorial environment is also associated with relatively stable conditions, including minimal ultraviolet radiation and ambient humidity levels ranging from 40% to 50% during the dry season.

Behavioral observations suggest sexual differences in microhabitat use. Post-breeding, females are typically found in leaf litter, while males occupy moss-covered stones along stream margins, which they use as calling sites throughout the year. These patterns imply potential site fidelity to breeding areas and a strong preference for specific microhabitats.

Further ecological studies are required to accurately delineate the spatial distribution, home range, and movement dynamics of A. balios in its natural habitat.

Communication and Perception

Like other Atelopus species, A. balios mostly relies on visual and chemical signals for communication. Males may use color displays, semaphoring and physical interactions during mating. Although most Atelopus species are not known for vocal communication, studies on a more closely related Atelopus species demonstrated the utilization of various low-intensity acoustic signals during courtship and territorial interactions. These findings suggest that vocal behaviour in the genus Atelopus species may be underreported due to the subtlety of their calls and the challenging nature of field recordings in their noisy stream habitats. Given that A. balios share similar streamside breeding habitats, it is plausible that these species may also produce a low frequency or short range accoustic signals during mating.

Studies on related species suggest that they may use pheromones to attract mates and establish territories.

• Communication Channels
• visual visual
• acoustic acoustic
• chemical chemical

• Other Communication Modes
• pheromones pheromones

• Perception Channels
• visual visual
• acoustic acoustic
• chemical chemical

Food Habits

Atelopus balios is an insectivorous species, primarily feeding on small invertebrates, including ants, beetles, and other arthropods. In captivity, they have been observed consuming a variety of small prey items, including fruit flies, black worms, weevils and crickets. Tadpoles, on the other hand, feed on algae and biofilms, which they scrape off submerged surfaces using specialized mouthparts. Toads absorb water through their skin; they do not drink. Due to A. balios species rarity, specific data on its foraging behavious is scarce.

• Primary Diet
• carnivore carnivore
  • insectivore insectivore
  • eats non-insect arthropods
• herbivore herbivore
  • algivore

• Animal Foods
• insects
• terrestrial non-insect arthropods
• terrestrial worms

• Plant Foods
• algae

• Other Foods
• microbes

• Foraging Behavior
• stores or caches food stores or caches food

Predation

Predation pressure on A. balios has not been well documented in the wild due to these population mainly being studied in captivity. However, there is one study reporting endemic climbing catfish from the Andes region preying on its juveniles. The species likely relies on cryptic coloration and toxic skin secretions to deter predators. The females lay their eggs under rocks, possibly to avoid predation. However, habitat disturbances may increase predation risks by exposing individuals to new predators.

• Anti-predator Adaptations
• aposematic aposematic
• cryptic cryptic

Ecosystem Roles

As both a predator and prey species, A. balios plays an integral role in maintaining ecological balance. It helps control insect populations while also serving as a food source for larger predators such as Andean catfish. Additionally, its tadpoles contribute to nutrient cycling in aquatic ecosystems by consuming biofilms and algae.

Economic Importance for Humans: Positive

The conservation and study of A. balios contributes to broader amphibian research, particularly in understanding disease resilience and habitat conservation strategies. Captive breeding programs provide educational opportunities and promote conservation awareness.

• Positive Impacts
• ecotourism ecotourism
• research and education
• controls pest population

Economic Importance for Humans: Negative

There are no known negative economic impacts associated with A. balios . However, its conservation requires financial resources and habitat protections, which may conflict with agricultural as well as land development interests in Ecuador.

• Negative Impacts
• injures humans
  • poisonous poisonous

Conservation Status

Atelopus balios is classified as Critically Endangered by the IUCN Red List, primarily due to habitat loss and chytridiomycosis outbreaks. The species is not listed under the US Federal List, or State of Michigan List, but it is under protection through CITES Appendix I, which regulates its international trade. Conservation efforts include habitat restoration, ex-situ breeding programs, and disease mitigation strategies.

A research was done on A. exiguus that highlighted the potential importance of high-elevation microhabitats and streamside moss cover in Atelopus survival. For A. balios , similar conservation strategies—like preserving stream buffer zones and reducing deforestation in montane corridors—could be essential for maintaining breeding habitats.

Citizen Conservation highlights A.balios as part of a multinational conservation breeding effort, led by the Jambatu Center. These initiatives not only aim to preserve its genetic line but also investigate resistance mechanisms to chytridiomycosis.

Other Comments

This species was thought to be extinct in 1995, but a remnant population was re-discovered in 2010 at Cerro Las Hayas, Provincia Guayas. The continued survival of A. balios hinges on conservation programs and habitat protection measures. This endangered member of the Atelopus genus has also been ravaged by a widespread chytrid fungus, Batrachochytrium dendrobatidis , which leads to chytridiomycosis. Research into its disease resistance, ecological role, and reproductive biology remains crucial for preventing extinction.

Note that this species is highly toxic due to the defensive chemicals secreted by the toad’s skin. While specific studies on their toxicity to humans are lacking, it is advised to practice caution when interacting with this species to avoid any adverse effects.

Additional Links

AmphibiaWeb

Encyclopedia of Life

Contributors

Pasangi Leyanawanniarachchi (author), Texas State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

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Astudillo, P., R. Jimenez, D. Siddons, B. Borja. 2022. "New Occurrences and Habitat Description of Southern Ecuador Endemic Frog Atelopus exiguus (Anura: Bufonidae) from a Conservation Hotspot in the High Andes.. Revista Peruana de Biologia , Vol 29. No. 3: e22742.

Augustine, L., L. Coloma, P. Vargas-Mena, . Elden. 2023. Notes on the Ex-Situ Maintenance and Reproduction of the Spotted Harlequin Frog, Atelopus balios (Bufonidae).. Herpetological Review , vol. 54, no. 4: 575-581.

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Coloma, L., D. Almedia-Reinoso. 2012. Ex Situ Management of Five Extant Species of Atelopus in Ecuador: Assisted Reproduction Essays for A. balios, A. elegans, A. nanay, A. spumarius, and A. sp. Amphibian Ark Newsletter , Vol 20: 9-12.

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Cruz - Garcia, K., N. Zapata, J. Perez - Correa. 2023. First Documented Case of Predation on the Río Pescado Jambato Toad (Atelopus balios Peters, 1973) by the Andean Catfish (Astroblepus sp.) on Cerro De Hayas, Naranjal, Ecuador.. Herpetology Notes , vol. 16: pp. 423-425.

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