Members of our research team, colleagues and friends recently attended the 9th World Congress of Herpetology, 5-10th January, 2020, at the University of Otago, Dunedin, New Zealand. It was an excellent congress, and there was a large contingent of amphibian chytridiomycosis researchers there!
Tolerance and resistance in defence against amphibian chytridiomycosis
Grogan L (1,2), McCallum H (1)
(1) Environmental Futures Research Institute, Griffith University
(2) School of Environment, Science and Engineering, Southern Cross University
Animal defences against infection involve two distinct but complementary mechanisms: tolerance and resistance. Tolerance measures the animal host’s ability to limit detrimental effects from a given infection, whereas resistance is the ability to limit the intensity of that infection. The study of host tolerance to infection is a burgeoning area in the field of animal disease ecology. Unlike resistance, tolerance does not affect pathogen fitness, and hence does not promote antagonistic counteradaptation. There is a vast range in amphibian responses to infection with the main fungal agent of the worst vertebrate disease, chytridiomycosis (Batrachochytrium dendrobatidis; Bd). Here, we quantify measures of tolerance and resistance across the amphibian chytridiomycosis literature, comparing species, life-stages and individual level variation. Infection tolerance is important for the dynamics and co-evolution of Bd infection within amphibian communities. Some frogs die from chytridiomycosis infection loads that others can tolerate without detrimental effects. Furthermore, some frogs harbour intense infections of > 8 million zoospore equivalents, consistent with the concept of superspreading. Tolerant amphibian life-stages such as tadpoles can harbour chytridiomycosis in their mouthparts but do not die from disease. Such tolerant tadpoles can then rescue a population despite high mortality of adults, or alternatively act as reservoirs for infection. Sympatric species, and tolerant superspreaders may also act as infection reservoirs, promoting pathogen persistence, maintaining high force of infection, and driving less tolerant hosts to extinction. Improving our understanding of infection tolerance and resistance promises powerful new strategies for understanding and mitigating infectious diseases.