Experimental evidence for a cost of resistance to the fungal pathogen, Batrachochytrium dendrobatidis, for the palmate newt, Lissotriton helveticus

Abstract

BackgroundBatrachochytrium dendrobatidis (Bd), the causative agent of chytridiomycosis, is decimating amphibians worldwide. Unsurprisingly, the majority of studies have therefore concentrated on documenting morbidity and mortality of susceptible species and projecting population consequences as a consequence of this emerging infectious disease. Currently, there is a paucity of studies investigating the sub-lethal costs of Bd in apparently asymptomatic species, particularly in controlled experimental conditions. Here we report the consequences of a single dose of B. dendrobatidis zoospores on captive adult palmate newts (Lissotriton helveticus) for morphological and behavioural traits that associate with reproductive success.ResultsA single exposure to ~2000 zoospores induced a subclinical Bd infection. One week after inoculation 84% of newts tested positive for Bd, and of those, 98% had apparently lost the infection by the day 30. However, exposed newts suffered significant mass loss compared with control newts, and those experimental newts removing higher levels of Bd lost most mass. We found no evidence to suggest that three secondary sexual characteristics (areas of dorsal crest and rear foot webbing, and length of tail filament) were reduced between experimental versus control newts; in fact, rear foot webbing was 26% more expansive at the end of the experiment in exposed newts. Finally, compared with unexposed controls, exposure to Bd was associated with a 50% earlier initiation of the non-reproductive terrestrial phase.ConclusionsOur results suggest that Bd has measureable, but sub-lethal effects, on adult palmate newts, at least under the laboratory conditions presented. We conclude that the effects reported are most likely to be mediated through the initiation of costly immune responses and/or tissue repair mechanisms. Although we found no evidence of hastened secondary sexual trait regression, through reducing individual body condition and potentially, breeding season duration, we predict that Bd exposure might have negative impacts on populations of palmate newts through reducing individual reproductive success and adult recruitment.

Amphibian skin microbiota exhibits temporal variation in community structure but stability of predicted Bd-inhibitory function

“…We used a bioinformatics approach to identify OTUs that can 'potentially' inhibit Bd (Kueneman et al, 2015(Kueneman et al, , 2016. Given that we found this pathogen on newts and that it has measurable sublethal effects on a related European newt species (Cheatsazan et al, 2013), it is likely exerting selective pressures on the studied hosts and their microbiota. Our results indicate that the proportion of predicted Bd-inhibitory reads did not vary temporally for two of three newt species, and aquatic and terrestrial individuals did not differ, suggesting that this Bd-inhibitory function was largely maintained despite structural variation.…”

A first screening of chytrid fungus Batrachochytrium in amphibians in French zoos

“…The Bd positive state of A. obstetricans and B. variegata is not surprising because animals are maintained in semi‐open enclosures where Palmate newts Lissotriton helveticus, an asymptomatic carrier of Bd (Cheatsazan et al ., ), are known to move freely between enclosures (Director of institution, pers. comm.).…”

Costs of resistance and infection by a generalist pathogen

“…Lastly, because resistance costs may be mediated by changes to host phe-notype, life history, behavior, or immunology (Rigby et al 2002), it is possible that costs are incurred without being detected. This may explain, in part, the mixed support for resistance costs in many animal systems, including Daphnia (this study; (Labb e et al 2010)), birds (Norris and Evans 2000), and amphibians (Cheatsazan et al 2013).…”