Over the last few days several members of our team (Laura Grogan, Mariel Familiar Lopez and Thais Sasso Lopes) attended the combined meeting of the Australian Society of Herpetologists and the Society for Research on Amphibians and Reptiles in New Zealand, held at Kindilan Camp, Redland Bay, Queensland, Australia.
It was a great conference with an impressive selection of research presented in two parallel sessions over 2.5 days. Below are the abstracts from our team members.
Batrachochytrium dendrobatidis presence within species: a review on ecological scales and influential variables
Sasso Lopes, Thais, Grogan, Laura and McCallum, Hamish
Environmental Futures Research Institute, Griffith University, Nathan, 4111, QLD, Australia.
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 amphibian chytridiomycosis, the worst disease ever recorded to affect biodiversity. 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 habitats at the population level, as well as presence of Bd across the landscape level. These studies have examined both environmental and intrinsic species-specific factors to explain the variable occurrence of Bd within species. The scale of interest has a profound influence on our understanding of which processes underpin the disease dynamics and on the scope of our conclusions and predictions. 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 2018 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 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.
Temporal variation of the skin bacterial community and Batrachochytrium dendrobatidis infection in the frog Philoria loveridgei
Familiar López, Mariel (1), Rebollar, Eria A. (2), Harris, Reid N. (3), Vredenburg, Vance T. (4) and Hero, Jean-Marc (5)
(1) School of Environment and Science, Griffith University, Gold Coast, QLD 4222; (2) Centre for Genomic Sciences, UNAM, Cuernavaca, Morelos 62210; (3) Department of Biology, James Madison University, Harrisonburg, VA 22807; (4) Department of Biology, San Francisco State University, San Francisco, CA 94132; (5) School of Science and Engineering, University of the Sunshine Coast, Maroochydore, QLD 4556.
Microbial symbiotic communities are ubiquitous in animals and plants as some can play
an important role in disease resistance of host, hence the focus of much current research.
Globally, amphibian population declines and extinctions have occurred due to chytridiomycosis, a skin disease caused by the pathogen Batrachochytrium dendrobatidis (Bd). Currently amphibian skin bacteria are increasingly recognized as important symbiont communities with a relevant role in the defense against pathogens, as some bacteria can inhibit the growth of Bd. This study aims to document the Bd infection status of wild populations of a terrestrial cryptic frog (Philoria loveridgei), and to determine whether infection status is correlated with changes in the skin microbial communities. Skin samples of P. loveridgei were collected along an altitudinal range within the species distribution in subtropical rainforests in southeast Australia. Sampling was conducted in two years during two breeding seasons with the first classified as a “La Niña” year. We used Taqman real-time PCR to determine Bd infection status and 16S amplicon sequencing techniques to describe the skin community structure. We found Bd-positive frogs only in the second sampling year with low infection intensities, and no correlation between Bd infection status and altitude, frog sex or size. Skin bacterial diversity was significantly higher in P. loveridgei frogs sampled in the 1st year than in the 2nd year. In addition, 7.4% of the total OTUs were significantly more abundant in the 1st year compared to the 2nd year. We identified 67 bacterial OTUs with a significant positive correlation between infection intensity and an OTU’s relative abundance. Forty-five percent of these OTUs belonged to the family Enterobacteriaceae. Overall, temporal variation was strongly associated with changes in Bd infection status and bacterial community structure of wild populations of P. loveridgei.
Chytridiomycosis causes catastrophic organism-wide metabolic dysregulation including profound failure of cellular energy pathways
Grogan, Laura F. (1), Skerratt, L.F. (2), Berger, L. (2), Cashins, S.D. (2), Trengove, R.D. (3, 4) and Gummer, J.P.A. (3, 4)
(1) Griffith Wildlife Disease Ecology Group, Environmental Futures Research Institute, School of Environment, Griffith University, Nathan, Queensland 4111, Australia; (2) One Health Research Group, College of Public Health, Medical and Veterinary Sciences, James Cook University, Townsville, Queensland 4811, Australia; (3) Separation Science and Metabolomics Laboratory, Murdoch University, Perth, Western Australia 6150, Australia; (4) Metabolomics Australia, Murdoch University Node, Murdoch University, Perth, Western Australia 6150, Australia.
Chytridiomycosis is among several recently emerged fungal diseases of wildlife that have
caused decline or extinction of naïve populations. Despite recent advances in understanding
pathogenesis, host response to infection remains poorly understood. Here we modelled a total of 162 metabolites across skin and liver tissues of 61 frogs from four populations (three long exposed and one naïve to the fungus) of the Australian Alpine Tree Frog (Litoria verreauxii alpina) throughout a longitudinal exposure experiment involving both infected and negative control individuals. We found that chytridiomycosis dramatically altered the organism-wide metabolism of clinically diseased frogs. Chytridiomycosis caused catastrophic failure of normal homeostatic mechanisms (interruption of biosynthetic and degradation metabolic pathways), and pronounced dysregulation of cellular energy metabolism. Key intermediates of the tricarboxylic acid cycle were markedly depleted, including in particular α-ketoglutarate and glutamate that together constitute a key nutrient pathway for immune processes. This study was the first to apply a non-targeted metabolomics approach to a fungal wildlife disease and specifically to dissect the host-pathogen interface of Bd-infected frogs. The patterns of metabolite accumulation we have identified reveal whole-body metabolic dysfunction induced by a fungal skin infection, and these findings have broad relevance for other fungal diseases.