Many endangered amphibian species now survive in captive breeding facilities because they are susceptible to the amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd), which has caused widespread amphibian declines. Because Bd can use different hosts, some of which do not succumb to disease, it persists in nature, making it challenging to reintroduce susceptible species. Skin bacteria on amphibians may play a role in limiting Bd infection, so there is interest in using skin bacteria to provide protection for reintroduced frogs. To understand whether this might be effective, we assessed what happens to the skin microbiome when captive-reared individuals are placed back into natural habitats by using captive-bred, Limosa harlequin frogs, Atelopus limosus. Captive-reared frogs were housed individually in mesocosms at the field site and swabbed initially and then every week after placement in the mesocosms to assess the skin microbiome and Bd infection. We opportunistically swabbed wild conspecific A. limosus. In addition, we completed community-level amphibian surveys for Bd prevalence at the study site to place A. limosus infection into the context of the broader amphibian community.
Results/Conclusions
Overall, the skin microbiome of captive-born frogs, based on assessment of 16S rRNA gene amplicons, was significantly different than that of wild conspecifics. However, this changed following exposure to natural conditions. After only two weeks in mesocosms, the captive-reared frogs and wild conspecifics had similar skin bacterial community structure. This suggests that the skin-associated microbiome of captive-born amphibians fairly quickly reverts to the wild-type after placement in natural conditions. The overall Bd prevalence in wild stream-dwelling frogs at the site was 13%-27%, and 15% of the A. limosus in mesocosms became infected with Bd. We conclude that mesocosms are a suitable tool for systematically and repeatedly observing amphibians during release trials, that microbiomes can be rapidly restored to wild-type after release, and that captive-reared A. limosus remains vulnerable to infection from the amphibian chytrid fungus in their natural habitat.