First release trial of Atelopus limosus shows that animals rapidly recover a wild-type skin microbiome.

In 2017, Virginia Tech PhD students Angie Estrada and Daniel Medina conducted the first release trial of captive-bred Limosa Harlequin frogs at the Mamoni Valley Preserve. Their study aimed to closely observe how 1-year-old captive-bred animals would transition from captive conditions back into the wild. To soften the blow of the changing conditions, and to allow the researchers to capture the frogs again, they designed 30 square shaped mesocosms from plastic mesh. In reintroduction biology placing animals in a temporary field enclosure prior to release is known as a soft release. They filled the bottom layer with leaf litter collected from the forest floor that was rich in leaf-litter invertebrates, a diet quite different from the crickets and fruit-flies they are usually fed by staff at the Panama Amphibian Rescue and Conservation Center. Each mesocosm housed a single animal that was monitored daily  for a month and weighed and swabbed weekly.

It is known that captivity can alter skin microbiomes of amphibians and other captive animals, and that this is an important component of amphibian immune defenses. This study found that wild and captive Atelopus limosus had very different microbiomes, but that after a month living in mesocosms, the skin microbiome had rapidly changed to resemble the microbiome of wild individuals. One concern about bringing animals into captivity for prolonged periods is that animals might lose symbiotic microbes that help them to survive in the wild, which might reduce the fitness of captive-bred animals, but this study found that the skin microbiome was rapidly rewilded.

The mesocosms were a useful tool that protected the animals from larger predators, though one was killed by army ants. Female animals lost body condition more rapidly than males, but at the end of the trial their condition resembled that of wild-caught animals. About 15% of the animals became infected with the amphibian chytrid fungus in the first month compared to 13-27% Bd prevalence in wild amphibian community.

Estrada, A., Medina, D; Gratwicke, B, Ibáñez, R, Belden, L (2022) Body condition, skin bacterial communities and disease status: Insights from the first release trial of the Limosa harlequin frog, Atelopus limosus. Proceedings of the Royal Society B.