Anthropogenic trade and development have broken down dispersal barriers, facilitating the spread of diseases that threaten Earth’s biodiversity. We present a global, quantitative assessment of the amphibian chytridiomycosis panzootic, one of the most impactful examples of disease spread, and demonstrate its role in the decline of at least 501 amphibian species over the past half-century, including 90 presumed extinctions. The effects of chytridiomycosis have been greatest in large-bodied, range-restricted anurans in wet climates in the Americas and Australia. Declines peaked in the 1980s, and only 12% of declined species show signs of recovery, whereas 39% are experiencing ongoing decline. There is risk of further chytridiomycosis outbreaks in new areas. The chytridiomycosis panzootic represents the greatest recorded loss of biodiversity attributable to a disease.

Amphibians are known to possess a wide variety of compounds stored in their skin glands. While significant progress has been made in understanding the chemical diversity and biological relevance of alkaloids, amines, steroids, and peptides, most aspects of the odorous secretions are completely unknown. In this study, we examined sexual variations in the volatile profile from the skin of the tree frogBoana prasinaand combined culture and culture-independent methods to investigate if microorganisms might be a source of these compounds. We found that sesquiterpenes, thioethers, and methoxypyrazines are major contributors to the observed sex differences. We also observed that each sex has a distinct profile of methoxypyrazines, and that the chemical origin of these compounds can be traced to aPseudomonassp. strain isolated from the frog’s skin. This symbiotic bacterium was present in almost all individuals examined from different sites and was maintained in captive conditions, supporting its significance as the source of methoxypyrazines in these frogs. Our results highlight the potential relevance of bacteria as a source of chemical signals in amphibians and contribute to increasing our understanding of the role that symbiotic associations have in animals.

Global amphibian declines have been attributed to several factors including the chytrid fungal pathogen, Batrachochytrium dendrobatidis (Bd), that infects hosts’ skin and causes death by inhibiting immune response and impairing osmoregulatory function. Here, we integrate extensive new field data with previously published locality records of Bd in Colombia, a megadiverse and environmentally heterogeneous country in northwestern South America, to determine the relative importance of environmental variables and reproductive mode for predicting the risk of Bd infection in amphibians. We surveyed 81 localities across Colombia and sampled 2876 individual amphibians belonging to 14 taxonomic families. Through a combination of end‐point PCR and real‐time PCR analyses, Bd was detected in 338 individuals (12%) representing 43 localities (53%) distributed from sea level to 3200 m. We found that annual mean temperature and variables related with seasonality in precipitation and temperature appeared to define the most suitable areas for the establishment of the pathogen. In addition, prevalence of infection appeared to be higher in species with a terrestrial reproductive mode. Our study provides the first large‐scale study of the current and potential distribution of Bd in the biodiversity hotspot centered on Colombia. We hope the newly provided information on the extent of the distribution of the pathogen and the potential areas where Bd may impact the amphibian fauna will inform decision making by environmental authorities and future conservation action.

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