Abstract
Amphibians support symbiotic bacterial communities on their skin that protect against a range of infectious pathogens, including the amphibian chytrid fungus. The conditions under which amphibians are maintained in captivity (e.g. diet, substrate, enrichment) in ex situ conservation programmes may affect the composition of the bacterial community. In addition, ex situ amphibian populations may support different bacterial communities in comparison to in situ populations of the same species. This could have implications for the suitability of populations intended for reintroduction, as well as the success of probiotic bacterial inoculations intended to provide amphibians with a bacterial community that resists invasion by the chytrid fungus. We aimed to investigate the effect of a carotenoid-enriched diet on the culturable bacterial community associated with captive red-eyed tree frogs (Agalychnis callidryas) and make comparisons to bacteria isolated from a wild population from the Chiquibul Rainforest in Belize. We successfully showed carotenoid availability influences the overall community composition, species richness and abundance of the bacterial community associated with the skin of captive frogs, with A. callidryas fed a carotenoid-enriched diet supporting a greater species richness and abundance of bacteria than those fed a carotenoid-free diet. Our results suggest that availability of carotenoids in the diet of captive frogs is likely to be beneficial for the bacterial community associated with the skin. We also found wild A. callidryas hosted more than double the number of different bacterial species than captive frogs with very little commonality between species. This suggests frogs in captivity may support a reduced and diverged bacterial community in comparison to wild populations of the same species, which could have particular relevance for ex situ conservation projects.
Highlights
Symbiotic bacterial communities are commonly found in association with both animals and plants
Woodhams et al [9] found that a population of Rana sierrae persisting with Batrochochytrium dendrobatidis (Bd; the amphibian chytrid fungus) in Yosemite National Park (USA) had significantly more individuals with at least one anti-Bd bacterial strain associated with their skin than a nearby population of Rana muscosa that was naıve to the chytrid fungus and subsequently became extinct when Bd spread to the area
The Adonis model for diet, gender and the diet 6 gender interaction showed diet had a significant effect on the overall bacterial community associated with frogs (F1,13 = 2.868, p = 0.024), but gender (F1,13 = 0.815, p = 0.529) and diet 6 gender (F1,13 = 0.733, p = 0.618) did not
Summary
Symbiotic bacterial communities are commonly found in association with both animals and plants. Dillon et al [6] demonstrated a significant inverse relationship between the species richness of the gut of locusts (Schistocerca gregaria) and the growth of pathogenic bacteria (Serratia marcescens), as well as a significant decrease in the number of infected individuals with an increase in bacterial community diversity. Woodhams et al [9] found that a population of Rana sierrae persisting with Batrochochytrium dendrobatidis (Bd; the amphibian chytrid fungus) in Yosemite National Park (USA) had significantly more individuals with at least one anti-Bd bacterial strain associated with their skin than a nearby population of Rana muscosa that was naıve to the chytrid fungus and subsequently became extinct when Bd spread to the area. Lam et al [12] compared the same population of R. sierrae to another Bd-naıve population of R. muscosa in the area and found similar proportions of individuals in each population that hosted at least one anti-Bd bacterial strain, and this population of R. muscosa managed to persist when the chytrid fungus arrived a year later
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