Abstract
Few studies have examined the role hormones play in mediating clinical changes associated with infection by the parasite Batrachochytrium dendrobatidis (Bd). Glucocorticoid (GC) hormones such as corticosteroids (CORT) regulate homeostasis and likely play a key role in response to infection in amphibians. We explore the relationship between CORT release rates and Bd infection in tadpoles of the common midwife toad, Alytes obstetricians, using a non-invasive water-borne hormone collection method across seven populations. We further examined whether tadpoles of A. muletensis infected with a hypervirulent lineage of Bd, BdGPL, had greater CORT release rates than those infected with a hypovirulent lineage, BdCAPE. Finally, we examined the relationship between righting reflex and CORT release rates in infected metamorphic toads of A. obstetricans. We found an interaction between elevation and Bd infection status confirming that altitude is associated with the overall severity of infection. In tandem, increasing elevation was associated with increasing CORT release rates. Tadpoles infected with the hypervirulent BdGPL had significantly higher CORT release rates than tadpoles infected with BdCAPE showing that more aggressive infections lead to increased CORT release rates. Infected metamorphs with higher CORT levels had an impaired righting reflex, our defined experimental endpoint. These results provide evidence that CORT is associated with an amphibian’s vulnerability to Bd infection, and that CORT is also affected by the aggressiveness of infection by Bd. Together these results indicate that CORT is a viable biomarker of amphibian stress.
Highlights
The disease chytridiomycosis is caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd), a parasite that has contributed to the global decline in amphibian populations worldwidePLOS ONE | DOI:10.1371/journal.pone.0122685 April 20, 2015Chytrid Infection, Behavior and Corticosterone
The mean CORT release rates in the infected population of A. muletensis were significantly lower than the infected population of A. obstetricans, and we proposed that these differences were due to the lineage of Bd infecting the population
We found that CORT release rates of populations of Alytes obstetricans are affected by an interaction between elevation and infection status
Summary
The disease chytridiomycosis is caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd), a parasite that has contributed to the global decline in amphibian populations worldwide. Numerous factors may be associated with elevated CORT all of which may drive levels of Bd infection There is both species and population-level variation in susceptibility to infection with Bd [14]. Some populations of the common midwife toad (Alytes obstetricans) show high rates of mortality and population crashes owing to infection by Bd, whereas other infected populations appear stable [15,16,17]. Environmental variables such as precipitation, temperature and elevation can affect host susceptibility [18, 19]. This study provides a better understanding of the mechanistic factors associated with the dynamics of Bd infections
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