Amphibian larvae benefit from a warm environment under simultaneous threat from chytridiomycosis and ranavirosis

Abstract

Rising temperatures can facilitate epizootic outbreaks, but disease outbreaks may be suppressed if temperatures increase beyond the optimum of the pathogens while still within the temperature range that allows for effective immune function in hosts. The two most devastating pathogens of wild amphibians, Batrachochytrium dendrobatidis (Bd) and ranaviruses (Rv), co‐occur in large areas, yet little is known about the consequences of their co‐infection and how these consequences depend on temperature. Here we tested how exposure to Bd and subsequent exposure to Rv, followed by treatment at elevated temperatures (28 and 30°C versus 22°C) affected Bd and Rv prevalence, infection intensities, and resulting mortalities in larval agile frogs and common toads. We found multiple pieces of evidence that the presence of one pathogen influenced the prevalence and/or infection intensity of the other pathogen in both species, depending on temperature and initial Rv concentration. Generally, the 30°C treatment lowered the prevalence and infection intensity of both pathogens and, in agile frogs, this was mirrored by higher survival. These results suggest that if temperatures naturally increase or are artificially elevated beyond what is ideal for both Bd and Rv, amphibians may be able to control infections and survive even the simultaneous presence of their most dangerous pathogenic enemies.

Juvenile agile frogs spatially avoid ranavirus-infected conspecifics, but do not show generalized social distancing or self-isolation

“…Third, avoidance behaviour may be adaptive not only for non-infected individuals but for already infected ones as well: by avoiding infected conspecifics, they may lower the chance of re-infection with the same pathogen or with new ones. Higher doses of infection come with increased virulence and decreased average survival time in nature (Anderson & May 1978) and this is also true for larval agile frogs (Herczeg et al 2023). Further, by staying away from diseased conspecifics, infected individuals may avoid infection with additional new pathogens which may be more likely carried by individuals (co-)infected with Rv , and thereby evade potentially disastrous outcomes of co-infection (Herczeg et al 2021).…”

“…Reactions were run on a BioRad CFX96 Touch Real-Time PCR System. For further details see Herczeg et al (2023).…”

“…1A). For the maintenance of Rv cultures see more details in Herczeg et al (2023). We placed each froglet in a 6 cm diameter Petri dish filled with 8 ml RSW and containing 5×10 5 plaque forming unit (pfu) × ml -1 of the virus.…”

“…In the present paper, we examined how the behaviour of juvenile agile frogs Rana dalmatina changes when facing Rv (Herczeg et al 2023). To this end, we ran classic choice tests, where the focal and the stimulus individuals were spatially separated from each other by transparent and perforated walls.…”