Sublethal effects of a mass mortality agent: pathogen-mediated plasticity of growth and development in a widespread North American amphibian

Amphibians exhibit diverse responses to environmental challenges, but their responses to infection risk remain poorly understood. This study investigates how the presence of ranavirus, a deadly viral pathogen, affects growth, development, and resource allocation in wood frog ( Rana sylvatica [ Lithobates sylvaticus ]) tadpoles. Using three years of pond survey data from a wood frog metapopulation in northeastern Connecticut, USA, we compared tadpole physiological rates across three scenarios: ranavirus-free ponds, ponds with sustained ranavirus infection, and ponds experiencing ranavirus die-offs. In ranavirus-positive ponds, tadpoles exhibited increased growth and resource allocation early in their development. These differences waned following die-off events in some ponds but persisted where widescale infection did not lead to die-off. This study provides evidence that an important disease agent appears to induce growth and developmental responses in its host that may help tadpoles survive severe infection by providing a buffer against the associated energetic demands. Alternative hypotheses, such as size-biased mortality, should be evaluated in experiments aimed at evaluating underlying mechanisms.