| Summary: | Amphibians harbor beneficial skin bacteria that can contribute to host defense against chytridiomycosis, an infectious disease caused by the lethal fungal pathogen Batrachochytrium dendrobatidis (Bd). However, while skin-associated microbial communities may alter host infection risk, the structure of these complex microbial communities can be impacted by both biotic and abiotic factors. In a series of three studies, I investigated the natural temporal and spatial variation in bacterial communities on the skin of wild and captive-born amphibians using 16S rRNA gene amplicon sequencing to characterize bacterial community diversity. First, in a study examining the skin bacterial communities of two sympatric treefrog species (Agalychnis callidryas and Dendropsophus ebraccatus) at a single pond over multiple seasons and years, I found that annual, seasonal, and even daily fluctuations in temperature and rainfall changed the skin bacterial communities on these species. Second, I further investigated the impact of seasonality and rainfall on amphibian skin bacterial communities with a study of the bacterial communities on Craugastor fitzingeri, a common terrestrial species, along a rainfall gradient, and five co-occurring amphibian species at a single site. The strong wet and dry seasonality in the tropical lowland forest impacted the bacterial communities of multiple stream-dwelling co-occurring species, but the nature of the changes differed among the frog species. For C. fitzingeri sampled along the rainfall gradient, I found there was variation in bacterial community structure among sites, although this was not correlated with the latitudinal rainfall gradient. Finally, I investigated the challenges faced by captive-reared Atelopus limosus, an endangered amphibian species, after soft-release into natural habitat with the use of mesocosms. I found that the skin bacterial communities reverted to wild-type fairly quickly, body condition decreased to come closer to wild conspecifics, and 15% of the frogs became infected with Bd during the 27 day trial in mesocosms. Overall, I found that skin bacterial communities of lowland amphibians change across time and space, that variation sometimes correlates with environmental conditions at the time and the site of sampling, and that skin bacterial communities on captive-born frogs revert to wild-frog's state soon after soft-release to natural habitat. === Doctor of Philosophy === Beneficial bacteria found on amphibian skin can provide protection against an infectious disease caused by the lethal amphibian chytrid fungus (Batrachochytrium dendrobatidis), that has been linked with the decline and extinction of amphibian species worldwide. However, while skin bacterial communities may play a key role in determining disease outcome, these complex microbial communities can be impacted by biological and environmental factors. In a series of three studies, I investigated the natural variation in skin bacterial communities on wild and captive-born amphibians through time and space using modern DNA sequencing technologies to characterize bacterial community diversity. First, in a study examining the skin bacterial communities of two treefrog species at a single pond over multiple years and seasons, I found that annual, seasonal, and even daily fluctuations in temperature and rainfall changed the skin bacterial communities on these species. Second, I further investigated the impact of seasonality and rainfall with a study sampling the skin of one common frog species along a rainfall gradient, and five amphibian species at a single site across seasons. The strong wet and dry seasonality in the tropical lowland forest impacted the bacterial communities of multiple species found near streams, but the nature of the changes differed among the different frogs. For the common species sampled along the rainfall gradient, I found there was variation in bacterial community structure among sites, although this was not correlated with the rainfall gradient. Finally, I investigated the challenges faced by captive-reared Atelopus limosus, an endangered amphibian species from Panama, after release into field enclosures in the natural habitat. I found that the skin bacterial communities reverted to wild-type fairly quickly, body mass decreased to come closer to wild frogs of the same species, and 15% of the frogs became infected with the chytrid fungus during the 27 day trial in the field enclosures. Overall, I found that skin bacterial communities of lowland amphibians change across time and space, that variation is sometimes linked with environmental conditions at the time and site of sampling, and that captive-born frogs revert to wild states soon after release to natural habitat.
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