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.

Ex situ conservation is an important tool for the prevention of species extinction in amphibians. Currently, there is limited information on the nutritional requirements of amphibians in captivity, and there have been anecdotal reports of skin colour degradation in captive amphibians. Amphibians use carotenoids for skin pigmentation, and because carotenoids are only obtainable through the diet, colour degradation could result from limited carotenoid availability. Studies of other vertebrate taxa have shown that carotenoids contribute to health and reproductive success; however, their importance to amphibians is currently unknown. We assessed the influence of carotenoids on the health and development of red‐eye tree frogs (Agalychnis callidryas) during larval and post‐metamorphic stages, and looked at effects on skin colour and reproductive success. Carry‐over effects of larval exposure to carotenoids were also investigated, and the effects of carotenoids on skin colour development and degradation in adulthood were examined. Carotenoids did not significantly influence larval growth or survival; however, post‐metamorphic carotenoid availability significantly increased growth rate in female but not in male frogs. Frogs fed a carotenoid diet post‐metamorphosis had significantly redder skin than controls, and larval carotenoid exposure significantly influenced post‐metamorphic skin colour. Fecundity was significantly higher in female frogs raised on a carotenoid diet post‐metamorphosis compared with controls. Finally, skin colour did not change in adulthood despite changes in dietary carotenoid availability, which suggests that there is a critical period during post‐metamorphic growth for deposition of carotenoids in the skin. We have shown that carotenoids influence the development, phenotype and reproductive success of A. callidryas, and these important nutrients should therefore be considered when nutritional recommendations for amphibians are made.

Amphibians have recently experienced unprecedented declines in the wild, the causes of which are often difficult to mitigate. This has increased the importance of ex situ conservation; however, long-term maintenance and breeding of amphibians in captivity often has limited success. In vertebrates, vitamin D is required for calcium homeostasis and is produced endogenously in skin exposed to ultraviolet (UV) light; however, UV light can be harmful to amphibians in some instances. Carotenoids are dietary pigments that may provide protection from UV light. The aim of this study was to assess the protective capability of carotenoids against the potentially harmful effects of UV light in Silurana (=Xenopus) tropicalis larvae raised in an enhanced or limited UV environment. Tadpole survival and the size and developmental stage reached by the end of the study period were measured. Carotenoids had a significantly positive effect on developmental rate in both UV-limited and UV-enhanced environments. Larvae in an enhanced UV environment were significantly larger than those raised under a limited UV environment, irrespective of diet. Carotenoid-fed larvae tended to have increased survival in relation to those raised without carotenoids, but only in a limited UV environment. Carotenoids appear to provide little protection against UV light in this case. The role of carotenoids in amphibian health has not previously been studied. We show that carotenoid availability significantly influences development and may increase survival in S. (X.) tropicalis larvae. This finding may have important implications for recommendations made on the nutrition of amphibians in captivity.

There are a limited number of feeder-invertebrates available to feed captive insectivores, and many are deficient in certain nutrients. Gut-loading is used to increase the diversity of nutrients present in the captive insectivore diet; however, little is known about delivery of carotenoids via gut-loading. Carotenoids may influence health and reproduction due to their roles in immune and antioxidant systems. We assessed interspecific variation in carotenoid accumulation and retention in three feeder-cricket species (Gryllus bimaculatus, Gryllodes sigillatus and Acheta domesticus) fed one of three diets (wheat-bran, fish-food based formulated diet, and fresh fruit and vegetables). Out of the three species of feeder-cricket in the fish-food-based dietary treatment group, G. bimaculatus had the greatest total carotenoid concentration. All cricket species fed the wheat-bran diet had very low carotenoid concentrations. Species on the fish-food-based diet had intermediate carotenoid concentrations, and those on the fruit and vegetable diet had the highest concentrations. Carotenoid retention was poor across all species. Overall, this study shows that, by providing captive insectivores with G. bimaculatus crickets recently fed a carotenoid-rich diet, the quantity of carotenoids in the diet can be increased.

Scanning electron microscopy was used to examine the surfaces of 21 species of tadpoles from six families, from Gosner Stage 25/26 until close to metamorphosis. Contrary to most previous reports, ciliated epidermal cells persisted until late stages in many but not all species and not at all locations examined. The commonest location for ciliated cells was around the nostrils, suggesting a role in chemosensation. Ciliated cells also occurred around the circumference of the eye, suggesting a cleaning role. Several species had ciliated cells on the tail. The densest, most regular arrays of ciliated cells occurred in species that tend to hang motionless in still-water pools, suggesting a respiratory function for these cells.