title: From skin to water: Chytrid fungus in Fleay's barred frog populations and their rainforest streams
Creators: name: Sasso Lopes, Thais
Publisher: name: Griffith University
Year: 2023
Subjects: subject: infectious disease
subject: amphibians
subject: Mixophyes fleayi
subject: Batrachochytrium dendrobatidis
subject: environmental DNA

description: Infectious diseases can be catastrophic. When emerging pathogens encroach on naïve populations, they can impose major environmental costs by triggering species declines and even extinctions. Among amphibians, a fatal skin disease caused by the fungus Batrachochytrium dendrobatidis (Bd) has attracted warranted attention globally. There are extensive reports of Bd representing a key threat to anuran diversity and being the cause of amphibian community declines within large areas. However, Bd presence and impacts are highly variable across the landscape depending on a range of physiological, environmental, or genetic factors. Anuran collapses, therefore, can vary greatly both between and within species. Without adequate understanding of the drivers of pathogen occurrence and infection dynamics, it is hard to stay ahead of the impacts of infectious disease and implement effective conservation practices to counter species losses. This thesis begins with an introductory synthesis of the latest literature and underlying broad themes. I then reviewed two decades of literature evaluating drivers of spatial heterogeneity in Bd presence across amphibian populations. The results in chapter 2 highlighted that despite Bd being the most well investigated amphibian pathogen, there is a major mismatch between the geographic locations surveyed and the distribution of global amphibian diversity, hotspots of highly threatened species, or hubs of amphibian declines due to Bd. I found that species at least risk of extinction were overrepresented in the literature. The results also revealed that the main variables examined in understanding Bd occurrence have been limited to environmental factors, with few studies examining genetic, host traits or other biotic aspects of host-Bd dynamics. In Australia, where Bd caused severe declines since the late 1970s, very few to no studies have been conducted concerning the heterogeneity in occurrence of Bd across populations of endangered frog species. Despite some evidence of stabilised and recovering populations, the infection dynamics and the distribution-wide species status for the Fleay’s barred frog, Mixophyes fleayi, are still unclear. A better understanding of mechanisms driving M. fleayi populations to persist and recover might allow application of enhanced management for other species that are still vulnerable or declining due to Bd. Equally relevant, temporary recovery trends in some populations do not necessarily mean that the species is no longer vulnerable to chytridiomycosis, nor that Bd is not having an effect along with other threatening processes. Given predictions of niche reduction due to climate change, M. fleayi is likely still at risk of irreparable declines. Thus, targeted surveys to determine M. fleayi occurrence and infection levels across the species’ distribution are of high priority. [...]