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Laura and Thais presented at the World Congress of Herpetology in New Zealand

Dr. Laura Grogan was invited to speak at a symposium on "Amphibian Disease Susceptibility in a Changing World" at the World Congress of Herpetology in Dunedin, New Zealand. She presented her work on "Tolerance and resistance in defence against amphibian chytridiomycosis".

The symposium hosted talks from a number of fellow amphibian researchers including Jamie Voyles, Jessica Hua, Cherie Briggs, Michel Ohmer, Guilherme Becker, and Ben Scheele.

PhD student Thais Sasso Lopes also presented her literature review on factors influencing disease occurrence variation. They both enjoyed a week of learning and meetings with researchers from more than 50 countries that didn't want to miss the world congress which only takes place every 4 years.

Laura and Thais presentation:

Title: Tolerance and resistance in defence against amphibian chytridiomycosis

Authors: Grogan L (1,2), McCallum H (1)

(1) Environmental Futures Research Institute, Griffith University

(2) School of Environment, Science and Engineering, Southern Cross University

Abstract: 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.

Title: Differential outcome of chytridiomycosis within species: a review on influential variables

Authors: Sasso Lopes T (1), Grogan L (1), McCallum H (1)

(1) Griffith University

Abstract: Since the identification of the infectious agent Batrachochytrium dendrobatidis (Bd) 20 years ago, numerous studies have helped to build solid documentation on the impact of chytridiomycosis worldwide. Bd presence in frogs has been investigated over a broad range of ecological scales. Studies have extended from differences in infection load within individuals, disease prevalence among populations, as well as presence of Bd across the landscape level. These studies examined both environmental and intrinsic species-specific factors to explain the variable occurrence of Bd within species in order to understand which processes underpin the disease dynamics and differential disease outcome. To evaluate the breadth of studies performed to date we quantitatively reviewed the Bd literature, and classified studies with regard to the spatial scale explored, methodological design and overall findings. We systematized which variables were most strongly associated with heterogeneity of disease occurrence. Among the 80 peer-reviewed papers published between 2004 and 2019 that fitted our criteria, air temperature and rainfall or humidity were commonly investigated environmental parameters. Variables such as life stage, distance to urban areas or zooplankton composition were seldom investigated, but were shown to influence Bd prevalence or infection load among different populations of the same species. Chytridiomycosis remains a dire threat to amphibians worldwide, and an intricacy of factors influences its occurrence and consequently its effects. Our review emphasises that understanding the complexity of Bd impact requires an integration of studies tackling Bd-host interaction at multiple scales and perspectives.

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