An investigation into the impacts of an emerging viral pathogen on wild UK populations of European common frog (Rana temporaria).

Abstract

Ranaviruses, the causative viral pathogens behind one of the most widespread and deadly amphibian diseases have been present in the UK since at least the late 1980s. They have been implicated as the cause of mass mortality events and associated populations declines observed in the European common frog (Rana temporaria). Early public engagement in the study of ranaviral emergence in the UK led to the formation of a unique network of mostly privately owned field sites, each housing a population of R. temporaria of known ranaviral disease history. Working within this comparative network of populations, I investigated how a history of ranaviral disease impacts upon various aspects of R. temporaria populations. An experimental infection trial demonstrated that prior population history of ranaviral infection does not influence the ability of metamorphic R. temporaria to control pathogen burdens after primary infection, though individual body weight does. A comparative wild transcriptomics study, implemented using novel methodologies, found no evidence that a positive history of ranavirosis results in significant functional changes in the transcriptome of frog populations. An extensive study of the skin microbiomes of wild R. temporaria revealed for the first time that the commensal bacterial communities present on the skin of wild amphibians might be as intimately linked to ranaviruses as they are to other amphibian pathogens. And finally, skeletochronological analysis of wild adult R. temporaria provided first evidence that infection with a ranavirus reduces the age distribution in positive disease history populations, potentially altering host life history strategies and heightening risk of local extinction.