Captivity, reintroductions, and the rewilding of the amphibian microbiome

Abstract Many studies have noted differences in microbes associated with animals reared in captivity compared to their wild counterparts, but few studies have examined how microbes change when animals are reintroduced to the wild after being reared in captivity. As captive assurance populations and reintroduction programs increase, a better understanding of how microbial symbionts respond during animal translocations is critical. We examined changes in microbes associated with boreal toads (Anaxyrus boreas boreas), a threatened amphibian, after reintroduction to the wild following captive rearing. Previous studies demonstrate that developmental life stage is an important factor in amphibian microbiomes. We collected 16S marker-gene sequencing datasets to investigate: i) comparisons of the skin, mouth, and fecal bacteria of boreal toads across four developmental life stages in captivity and the wild, ii) tadpole skin bacteria before and after reintroduction to the wild, and iii) adult skin bacteria during reintroduction to the wild. We demonstrated that differences occur across skin, fecal, and mouth microbial communities in captive versus wild boreal toads, and that the degree of difference depends on developmental stage. Skin bacterial communities from captive tadpoles were more similar to their wild counterparts than captive post-metamorphic individuals were to their wild counterparts. When captive-reared tadpoles were introduced to a wild site, their skin bacteria changed rapidly to mirror wild tadpoles. Similarly, the microbiome of reintroduced adult boreal toads also shifted to mirror that of wild toads. Our results indicate that the microbial signature of captivity in amphibians does not persist after release into natural habitat.