Clinical and naturalistic substrates differ in bacterial communities and in their effects on skin microbiota in captive fire salamanders (Salamandra salamandra)

The fire salamander (Salamandra salamandra and its relatives) is of increasing priority for ex situ conservation due to the spread of the fungal pathogen Batrachochytrium salamandrivorans in Europe. In captivity, the species may be maintained on a clinical paper-based or a naturalistic substrate, either of which has its own advantages and disadvantages. However, the impact of these two substrates on bacterial microbiotas within an enclosure and on the salamanders themselves is unknown. To investigate this, we maintained captive fire salamanders on either paper towels or a naturalistic substrate and quantified the culturable microbiotas of both substrates across the one-week lifespan of a paper towel and of the salamanders themselves over a six-month period. We found significant differences in the bacterial communities associated with the two substrates. Over a week-long period, there were major fluctuations in the community composition and abundance on paper towels while on the naturalistic substrate bacterial communities were relatively stable. The skin microbiota of salamanders were indistinguishable at the beginning of the study but after six months differed significantly between the two treatments, although the bacterial morphotypes present remained relatively similar compared with changes between substrates. These data show that husbandry protocols may have a strong influence on the culturable bacterial communities to which captive amphibians are exposed. Nevertheless, the animals were apparently able to maintain their own microbiota to a considerable degree. These findings should be borne in mind when determining husbandry protocols. Given the relative benefits of both types of enclosure, it is possible that a hybrid approach could be used whereby a small amount of naturalistic substrate is provided in a container within an otherwise clinical enclosure, to act as a bacterial reservoir.