A lethal fungal pathogen causes widespread disruption to amphibian hosts, but responses differ by species

Nicholas C. Wu

This is a plain language summary of a Functional Ecology research article which can be found here.

Emerging infectious diseases have contributed to the ongoing loss of biodiversity worldwide. How species respond to infectious pathogens depends on a myriad of environmental factors, as well as differences in the host and pathogen traits. However, the onset of disease largely depends on the amount of a pathogen on the host. The more pathogen on a host, the more likely the host will develop an infectious disease. Different ‘traits’ related to an animal’s fitness such as body condition, reproduction or metabolic rate may be more sensitive to pathogen load. Understanding similarities in trait sensitivity can help us to understand disease impact and help wildlife management efforts.

To test the relationship between pathogen load and trait disruption across species and studies, I used meta-analysis, which is a statistical technique for summarizing, and drawing conclusions from collections of studies. Meta-analysis can reveal commonalities and differences in response between studies, as well as biases in study preferences and localities.

Impact of Batrachochytrium dendrobatidis infection on biological and functional traits in amphibians (Illustration: Nicholas Wu)

To illustrate the power of meta-analysis, I used amphibians and the chytrid fungus pathogen as a case model. Chytridiomycosis, caused by the fungal pathogen, Batrachochytrium dendrobatidis (Bd), is considered the most devastating single disease for biodiversity, contributing to the decline of at least 501 amphibian species globally.

Across 69 studies with 52 species, I show that Bd disrupts all sorts of traits relating to physiology, behaviour, and reproduction, and show that juveniles die at lower pathogen load than adults. Death depended on both the pathogen load and how long the individual was exposed for as juveniles, while death of adults depended on pathogen load only. I also show studies tend to bias towards immune response, body condition, and survival, while traits such as locomotor performance and metabolic rate were lacking. With the growing number of emerging infectious diseases, meta-analytic approaches can be a useful tool to better understand disease dynamics in an ecological context.