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- Materials and methods
- Supporting Information
The amphibian chytrid fungus Batrachochytrium dendrobatidis is a major cause of frog declines globally.
Two recent Maxent models predict high environmental suitability for B. dendrobatidis in south-western Australia despite severe summer drought and many frog species with direct development or breeding in ephemeral water bodies: features often associated with absence of B. dendrobatidis.
We determined B. dendrobatidis occurrence and intensity of infection, in 15 populations of Crinia georgiana, a frog that breeds in ephemeral ponds, to assess (i) current validity of claims about environmental suitability, (ii) risk of decline against recent suggestions of 100% prevalence and chytrid loads of > 10 000 zoospore equivalents per frog as predictors of imminent decline and (iii) assess apparent change in prevalence over 20 years.
Batrachochytrium dendrobatidis occurred on 40–100% of frogs at all sites and in water samples at 11 sites but infection levels were generally well below 10 000 zoospore equivalents per frog. Based on immediate and 5-year climate averages, higher rainfall, more rain days and temperatures > 3 °C but < 30 °C were positively correlated with infection levels – consistent with the known physiology and growth patterns of B. dendrobatidis. Overall infection levels have changed little from 1992 to 2008.
Synthesis and applications. Predicted and realized high environmental suitability for B. dendrobatidis is not correlated with frog decline in south-western Australia. Innate or acquired immunity, chytrid strain type and limited opportunities for chytrid growth may all explain absence of chytrid impacts. Occurrence of Batrachochytrium dendrobatidis is not a current critical management issue for conservation managers in south-western Australia despite a known presence since 1985. Models predicting high environmental suitability for chytrid in Mediterranean climate zones should be interpreted cautiously in the absence of documentation of current, rather than historic, chytrid loads and a clear evaluation of any occurrence of chytrid on frog survival.