Dr. Madelyn Mangan's PhD conferred!

Dr. Madelyn Mangan's PhD has recently been conferred! Congratulations Maddy!

Maddy's PhD thesis "Mechanisms of amphibian population recovery after declines due to chytridiomycosis" received Griffith University's Award of Excellence in a Research Thesis due to unanimous opinion of the examiners on the significance of her work and its contribution to the field of research. Such unanimous agreement amongst examiners is justified only by a very high standard of work.

Congratulations on this exceptional achievement, Maddy!!

Abstract

The amphibian skin disease chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), has been a driver of unprecedented amphibian extinctions and mass mortalities around the world. A small proportion of Bd-affected taxa have shown signs of emerging recoveries, but the majority of susceptible species display either tenuous stabilisations or ongoing declines in association with the endemic presence of Bd. As amphibians will face growing anthropogenic threats in the 21st century (i.e. climate change, habitat loss), it is crucial to identify conservation interventions which most effectively mitigate the impact of chytridiomycosis on vulnerable species. Through investigations of two different amphibian systems, my thesis explores epidemiological, ecological, and genomic mechanisms which promote amphibian recoveries after Bd epidemics. In Chapter 1, I showed through epidemiological modelling that interventions which modify relative rates of recruitment can substantially alter pathogen-mediated competitive outcomes between species of an amphibian community. In Chapter 2, I demonstrated that the putatively recovering Fleay’s barred frog (Mixophyes fleayi) experienced range-wide genetic bottlenecks in association with Bd, but now shows signs of widespread genetic stabilisations and evidence of emerging genetic recoveries. In Chapter 3, I found that M. fleayi post-epidemic patterns of diversity at an immune locus associated with susceptibility to Bd (MHCIIβ1) were predominantly driven by genetic drift across disjunct populations rather than pathogen-mediated direction selection. Overall, my thesis demonstrates that mechanisms of amphibian recovery are multifaceted, interactive and highly dependent on ecological context. My genomic investigations additionally call attention to the need for post-epidemic genomic characterisation of species impacted by amphibian chytridiomycosis. Even in recovering species such as M. fleayi, strong Bd-associated genetic bottlenecks and low connectivity due to habitat fragmentation may compromise the long-term genomic viability of many amphibian populations.