Amphibians
Harlequin Toad
Atelopus · also called harlequin frogs, stubfoot toads
Harlequin toads were once among the most visible, boldly coloured amphibians of Central and South America’s mountain streams — and then, within a few decades, a single skin disease pushed the majority of the genus’s roughly 100 species to the edge of extinction or past it. A few, presumed lost for years, have since turned up alive again in isolated pockets, informally called Lazarus species by the researchers who thought they were gone for good.
Overview
Harlequin toads, genus Atelopus, are a group of around 100 species found along mountain streams from Costa Rica through the Andes and into the Amazon basin. Many display bold black-and-yellow or black-and-orange warning colouration, advertising toxic skin secretions to predators.
One of the worst collapses on record
The amphibian chytrid fungus has devastated the genus more severely than almost any other vertebrate group, leaving most species Critically Endangered, Extinct in the Wild, or Extinct — a crisis compounded by many species’ naturally tiny, stream-bound ranges. Some species thought gone for good have since been rediscovered in small surviving populations.
Status
Critically Endangered as a genus — a small number of more stable species remain, but ongoing captive breeding and disease research are considered essential to preventing further losses.
Harlequin Toad: common questions
Why have harlequin toads been hit so much harder by disease than many other amphibians?
The amphibian chytrid fungus infects and damages the skin, which many amphibians rely on heavily for breathing and regulating water and salt balance, and harlequin toads appear to be particularly vulnerable to this disruption, combined with the fact that many species live in the cool, high-elevation stream habitats where the fungus tends to thrive and spread most effectively. The genus's characteristic pattern of many species having naturally small, fragmented ranges tied to specific streams has also meant that once disease reaches a given population, there is often little nearby suitable habitat or connected population to allow natural recolonisation afterward.
What does it mean when a harlequin toad species is called a Lazarus species?
The term is used informally for a species that was not observed for so long, often many years or even decades, that it was widely presumed extinct by researchers, only to later be rediscovered surviving in a small, often isolated wild population that had simply gone undetected. Several harlequin toad species have followed exactly this pattern, and while a rediscovery is genuinely encouraging, these surviving populations are typically still extremely small and vulnerable, meaning a Lazarus species usually still faces a very serious ongoing risk of true extinction.
Are all harlequin toads brightly coloured?
Many, though not all, species display bold, high-contrast patterns of black combined with yellow, orange, red, or green, colouration that functions as a warning signal to predators about the toad's toxic skin secretions rather than as camouflage. Some harlequin toad species are more subdued or cryptically coloured instead, particularly those living in habitats or facing predator communities where a warning display would be less effective, so bright colouration, while common and iconic for the genus, is not a universal feature of every species within it.
What is being done to help harlequin toads survive?
Conservation efforts for the most threatened harlequin toad species include establishing captive assurance populations at zoos and dedicated amphibian conservation centres, researching ways to manage or reduce the impact of the chytrid fungus in the wild, protecting remaining stream and mountain forest habitat from further degradation, and continuing field surveys aimed at locating any additional surviving wild populations. For a small number of species, careful reintroduction of captive-bred individuals to protected wild sites is also being explored as disease management techniques and habitat conditions allow.