A project undertaken at Deakin University, and supervised by Prof Don Driscoll.
Prolonged drought associated with climate change is driving widespread loss of frogs from Australian landscapes, altering food webs and reducing ecosystem services. Environmental watering offers a way to prevent declines, but these watering solutions are complicated by interactions with the amphibian disease chytridiomycosis. Chytrid has driven declines in 43 Australian species including seven extinctions. Chytrid could interact with drought because it dies if it dries out, and its success depends on transmission to new vulnerable hosts. If land managers respond to drought by creating moist refuges and topping up breeding pools, they might also increase disease transmission.
We aimed to discover how environmental-water and chytrid interact to influence frog survival using a field experiment. We focused on the endangered Bibron’s toadlet (Pseudophryne bibronii) because drought and chytrid is suspected to have caused widespread declines. Bibron’s toadlets breed in small, ephemeral pools in autumn, a system with enormous potential for assistance through environmental-water because very small amounts of water are needed. We set up five “wet” sites where a water tank and reticulated pipes provided water to rooftile refuges, and five sites without added water. At each site we monitored frogs beneath tiles, and within natural refuges throughout the 2022 and 2023 breeding seasons. Upon each capture, frogs were swabbed for chytrid, the ventral surface of the frog was photographed for individual identification, and we measured soil pH, temperature and moisture. Chytrid infection and zoospore loads were determined with quantitative PCR.
Bibroni bellies.
There was no drought during the study, so adding water to pools to enhance survival was not needed and we could not evaluate whether added water increased survival during drought. Nevertheless, we found that adding water to rooftile shelters increased the risk of chytrid infection. We also found that as chytrid zoospore loads increased, the chances of recapture reduced, suggesting that P. bibroni is vulnerable to death once infected. On the other hand, we also found that some P. bibroni could clear themselves of chytrid, providing a potential pathway for populations to adapt to the disease. Chytrid infection risk increased with soil pH, temperature, moisture, and time into the breeding season.
We conclude that creating moist refuges should be avoided in normal and high rainfall years because there is no apparent increase in survival but there is an increase in chytrid infection. It remains critical to repeat our study during a drought period, where increased chytrid infection risk with watering may be countered by increased survival by avoiding desiccation. With chytrid infection potentially limited in low pH environments, there may be opportunities to experimentally reduce pH when adding water to refuges, and thus minimise the chytrid infection risk. Protecting amphibians from declines will become increasingly challenging as anthropogenic climate change brings more extreme drought, and diseases, spread by human activity, continue to take a toll. Ultimately, increasing biosecurity to prevent new diseases from spreading, and eliminating fossil fuel use are essential solutions. In the meantime, further research can help refine management responses that support biodiversity resistance to ongoing anthropogenic affronts.