|Common Name||Costa Rican Variable Harlequin Toad|
|Range||Costa Rica and Panama.|
The Costa Rican variable harlequin toad (Atelopus varius), also known as the clown frog, is a species of toad in the Bufonidae family. Once ranging from Costa Rica to Panama. Atelopus varius is now listed as critically endangered and has been reduced to a single remnant population near Quepos, Costa Rica (rediscovered in 2003) and is presumed to be extinct in Panama (IUCN). Recent variation in air temperature, precipitation, stream flow patterns, and the subsequent spread of a pathogenic chytrid fungus (Batrachochytrium dendrobatidis) linked to global climate change have been the leading cause of decline for Atelopus varius. Atelopus zeteki has been considered a subspecies of Atelopus varius, but is now generally considered a separate species.
The historic range of Atelopus varius stretched from the Pacific and Atlantic slopes of the Cordilleras de Tilaran mountain range in Costa Rica into western Panama. Suitable habitat includes both pre-montane and lower-montane zones as well as some lowland sites along rocky streams in hilly areas (ranging from 6 to 2000m in elevation). At present, Atelopus varius is restricted to a single lowland site along a stream and small tributary on the Pacific coastal range near Quepos, Costa Rica.
Habitat and Ecology
Atelopus varius is a diurnal toad often found on rocks or in crevices along streams in humid lowland and montane forests. It is primarily a terrestrial species, only entering the water during breeding season, relying on spray from streams for moisture.
Atelopus varius is slow moving and often remains in the same area for long periods of time. The conspicuous or aposematic coloration of Atelopus varius likely serves as a warning to potential predators of the toxicity of the frog's integument which contains tetrodotoxin, a potent neurotoxin. Its main food source is small arthropods that are most abundant during the dry season. The only known predator of Atelopus varius is a parasitic sarcophagid fly (Notochaeta bufonivora) which deposits its larvae on the surface of the frog's thigh. The larvae then proceed to burrow inside the frog and eat it from within. In addition, large land crabs have recently been observed attempting to prey on Atelopus varius but it is unclear what, if any, effect this has on the population.
In recent decades, Atelopus varius has become increasingly rare throughout its geographic range. The first incidence of its disappearance was recorded after a census conducted between 1990 and 1992 near Monteverde, Costa Rica revealed zero individuals where its population had previously peaked at 751 adults. By 1996, Atelopus varius was believed to be extinct throughout Costa Rica. However, subsequent surveys carried out by the rainmaker project in 2003 and 2005 rediscovered a population of the endangered frog on the Pacific coastal range near Quepos (IUCN). In Panama, mass mortality has drastically reduced populations of Atelopus varius in recent years and it is now believed to be locally extinct. At present only a single population of an estimated 60-95 individuals remains in an isolated location in Costa Rica.
Several theories related to changes in climatic patterns have been put forth to account for the rapid decline of Atelopus varius. A trend toward rising temperatures across the tropics in the late 1980s and early 1990s has been implicated in the declines of multiple lizard and amphibian species including several Atelopus spp. More recently, an observed global decline in amphibian species richness has been linked to an outbreak of the pathogenic chytrid fungus Batrachochytrium dendrobatidis. This pathogen can be transmitted between individuals through shed skin cells and is known to infect keratinized body surfaces where it can impair cutaneous respiration and osmoregulation thus resulting in mortality. Current attempts to preserve A. varius include a recently initiated captive breeding program as well as continued efforts to protect vital forest habitat (IUCN).
Recent testing indicates that the remaining population of Atelopus varius is presently free of chytrid infection. In order to avoid future transmission, monitoring is carried out twice annually by a small group of researchers following strict decontamination protocols. Additionally, the persistence of Atelopus varius is threatened by predation, habitat alteration, and the potentially detrimental effects of inbreeding. Current conservation efforts consist of population and microclimate monitoring, genetic studies, and habitat protection. Although evidence suggests that the current population is reproductively active and relatively stable, the long-term prognosis for Atelopus varius is uncertain.