Aim  We use novel data on the occurrence of the amphibian chytrid fungus Batrachochytrium dendrobatidis in Costa Rica to model its potential distribution in that country. Location  Lowland and montane areas of Costa Rica. Methods  We use published and new data on the presence of B. dendrobatidis on 647 amphibians (35 species). Screening was performed through histological techniques by which 156 sites were surveyed. Of these, 21 were found to have the amphibian chytrid. Maxent, a presence‐only distribution modelling technique, was used to create 100 predictions of B. dendrobatidis occurrence, of which the most accurate 10 (based on area under the receiver‐operating characteristic curve) were chosen to create a composite distribution model. This approach increased confidence in model predictions, distinguishing areas of high probability of occurrence and low variability across model runs (higher confidence) from those with high probability but high variability (lower confidence). Results  Predicted distribution patterns were not uniform along Costa Rica's mountains, where most amphibian declines have occurred. The pathogen was predicted to occur with greater probability on the Caribbean slopes than on the Pacific slopes. While high temperature seems to constrain the distribution of the pathogen, areas that also have small amounts of rainfall during the driest period of the year were predicted to have low probability of B. dendrobatidis occurrence. Main conclusions  The model predicts that the Santa Elena Peninsula and the Central Valley have low probabilities of B. dendrobatidis occurrence, suggesting that they could function as refuges for amphibians. In such refugial areas, one could expect B. dendrobatidis to be absent, or to be present in low abundance (rendering an epidemic outbreak of chytridiomycosis unlikely). Craugastor ranoides, which belongs to a group of frogs particularly sensitive to chytridiomycosis outbreaks, persists in the hot and seasonally dry Santa Elena Peninsula but disappeared in the nearby colder and more humid Guanacaste Volcanic Chain. This information suggests that climatic refuges, where environmental conditions prevent disease outbreaks, could be an important component in amphibian conservation.

Batrachochytrium dendrobatidis (Bd) has been associated with the severe declines and extinctions of amphibians in Costa Rica that primarily occurred during the 1980s and 1990s. However, the current impact of Bd infection on amphibian species in Costa Rica is unknown. We aimed to update the list of amphibian species in Costa Rica and evaluate the prevalence and infection intensity of Bd infection across the country to aid in the development of effective conservation strategies for amphibians. We reviewed taxonomic lists and included new species descriptions and records for a total of 215 amphibian species in Costa Rica. We also sampled for Bd at nine localities from 2015–2018 and combined these data with additional Bd occurrence data from multiple studies conducted in amphibian communities across Costa Rica from 2005–2018. With this combined dataset, we found that Bd was common (overall infection rate of 23%) across regions and elevations, but infection intensity was below theoretical thresholds associated with mortality. Bd was also more prevalent in Caribbean lowlands and in terrestrial amphibians with an aquatic larval stage; meanwhile, infection load was the highest in direct-developing species (forest and stream-dwellers). Our findings can be used to prioritize regions and taxonomic groups for conservation strategies.

In 1987 the amphibian decline crisis reached its apex in Costa Rica when at least 17 species experienced population crashes and subsequently went undetected for decades. The amphibian declines in Costa Rica were relatively well documented and came to exemplify the current global amphibian decline crisis. The Mesoamerica endemic frog clade, the Craugastor punctariolus species group, is one of most severely affected anuran clades, experiencing a loss of 26 out of 33 species throughout Mesoamerica. Eight species of C. punctariolus group frogs occur in Costa Rica, and all declined following the 1987 die-off; despite intensive surveys over the last 14 years, most remain undetected. To date, only one species in this group, the stream-breeding frog C. ranoides, in known to have a stable population, and only in the Santa Elena Peninsula. Here we document the rediscovery of another species, the South Pacific streamside frog C. taurus, in southeastern Costa Rica, representing the first sighting after fifteen years of searching. We discovered two previously unknown populations in Punta Banco, the driest section within the historical range, in an area representing only 4% of the historical distribution. Our findings add to the short but growing list of recently rediscovered amphibian species in Costa Rica and provide encouraging news in an otherwise discouraging situation for amphibian conservation. Additional research and monitoring are urgently needed to develop long-term management plans for this and other Critically Endangered species

Population declines and extinctions of numerous species of amphibians, especially stream-breeding frogs, have been linked to the emerging infectious disease chytridiomycosis, caused by the chytrid fungus, Batrachochytrium dendrobatidis. In Central America, most of the 34 species of the Craugastor punctariolus species group have disappeared in recent years in high- and low-elevation rainforests. Distribution models for B. dendrobatidis and the continuous presence of the extirpated stream-dwelling species, Craugastor ranoides, in the driest site of Costa Rica (Santa Elena Peninsula), suggest that environmental conditions might restrict the growth and development of B. dendrobatidis, existing as a refuge from chytridiomycosis-driven extinction. We conducted field surveys to detect and quantify the pathogen using Real-time PCR in samples from 15 species of frogs in two locations of tropical dry forest. In Santa Elena Peninsula, we swabbed 310 frogs, and only one sample of the species, C. ranoides, tested positive for B. dendrobatidis (prevalence <0.1%). In Santa Rosa Station, we swabbed 100 frogs, and nine samples from three species tested positive (prevalence = 9.0%). We failed to detect signs of chytridiomycosis in any of the 410 sampled frogs, and low quantities of genetic equivalents (between 0 and 1073) were obtained from the ten positive samples. The difference in the prevalence between locations might be due not only to the hotter and drier conditions of Santa Elena Peninsula but also to the different compositions of species in both locations. Our results suggest that B. dendrobatidis is at the edge of its distribution in these dry and hot environments of tropical dry forest. This study supports the existence of climatic refuges from chytridiomycosis and highlights the importance of tropical dry forest conservation for amphibians in the face of epidemic disease.