Dr. Josie Humphries' PhD conferred!

Dr. Josie Humphries' PhD has recently been conferred! Congratulations Josie!!

Josie's project aimed to explore the relationship between metamorphic reorganisation and susceptibility to the fungal pathogen Batrachochytrium dendrobatidis (Bd) in an endangered amphibian (Mixophyes fleayi). She exposed M. fleayi to Bd during the late larval stages (Gosner stage 35-38), and sampled blood (via cardiocentesis) and immune-associated organs (skin and liver) post-euthanasia from subgroups of animals at Gosner stages 40, 42 and 45 (stratified random sampling). She also collected samples opportunistically from moribund animals that were humanely euthanised at Gosner stage 45. She combined visual assessments, physiological measurements (Gosner stage, weight, snout-vent-length, and full body length), infection load data (quantified via qPCR), bioinformatics and histological analyses of tissues sampled from the same individuals to provide an integrated overview of the infection response of M. fleayi throughout the critical metamorphic stages.

Her PhD project was the first study to present Bd infection progression throughout metamorphosis, revealing temporary infection loss at the onset of metamorphic climax (Gosner stage 42), and the onset of major Bd-associated metabolic and immunological dysregulation in the final stages of metamorphosis (Gosner stage 45), leading to morbidity and infection clearance in animals before the completion of metamorphosis. Given the severity of amphibian declines and the continued impact of Bd infections worldwide, the widespread oversight of potentially critical developmental stages could have significant and long-lasting impacts on the survival of amphibian species. Bd-induced additive mortalities in a life stage that is extremely challenging to observe and measure in the field could thus represent an important but cryptic limiting factor for population persistence. The extensive mortalities observed during late metamorphosis could act as a bottleneck in wild populations, necessitating conservation strategies (e.g., via population head-starting and reintroduction) tailored towards the protection of these vulnerable stages.