La anomalous combination of temperature and precipitation It is behind sudden die-offs of frogs, toads and salamanders, according to a study led by the National Museum of Natural Sciences (MNCN-CSIC) together with the Joint Institute for Biodiversity Research and the Spanish Herpetological Association, published in Current Biology.
Far from attributing it only to the heat, the study reformulates the previous theory and raises the question Thermal-water mismatch theory: It is the interaction between temperature anomalies and changes in rainfall patterns that trigger pathogens and increase the mortality of amphibians, the most threatened group of vertebrates on the planet.
Key data from the study in Spain
The team analyzed almost 6.000 specimens sampled throughout Spain, covering cold and wet habitats as well as warm and dry ones, to relate infection peaks to unusual weather events.
Amphibians adapted to cold and humid climates suffered more infections by the fungus Batrachochytrium dendrobatidis (Bd) during periods abnormally hot and dry, while species native to warm and dry environments were more infected in unusually cold and humid phases.
In contrast, viruses circulating naturally in our populations thrived under conditions opposite to those of the fungus; this asymmetry explains their poor temporal coincidence despite sharing space.
Lead author Barbora Thumsová stresses that this is the first evidence that Precipitation anomalies, combined with thermal anomalies, govern the process and the same logic is confirmed for lethal viruses that affect amphibians.
Fungi and viruses: opposing dynamics and consequences
Chytidomycosis, caused by the fungus Bd—probably of Asian origin—damages the skin and can cause heart failure; is one of the main drivers of the global decline of frogs, toads, and newts as it is already distributed throughout the planet.
Ranavirosis, on the other hand, can trigger mass mortalities By proliferating and destroying skin tissue and internal organs, both pathogens respond to different climatic signals, requiring monitoring that takes both temperature and water into account.
The study warns about emblematic species such as the Pyrenean frog or the Betic midwife toad, which has survived for millions of years and is now exposed due to the loss of safe havens in an increasingly unpredictable environment.
Beyond their intrinsic value, amphibians act as indicators of the state of ecosystemsThey control insect pests and sustain food chains; their decline is a warning sign of deep environmental dysfunctions.
The team is already collaborating with managers to translate evidence into action: continuous monitoring of populations and pathogens, restoration of wetlands and refuge corridors, and models that integrate thermal and rainfall variations to anticipate outbreaks.
The evidence converges on a simple idea: when the pulse of heat and rain gets out of sync, pathogens find their window and amphibians lose room to maneuver; understanding this imbalance is key to gaining time and preventing further die-offs.
