Captivity, reintroductions, and the rewilding of the amphibian microbiome

Abstract/Summary

Many studies have noted apparent differences in microbes associated with animals reared in captivity compared to their wild counterparts. 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 of boreal toads (Anaxyrus boreas) after reintroduction to the wild following captive rearing. Boreal toads, a long-lived high elevation species, are endangered in Colorado primarily due to chytridiomycosis. Previous studies demonstrate that developmental life stage of boreal toads is an important factor in their microbiomes such that microbiomes change over the course of development. i) comparisons of the skin, mouth, and gut bacteria of boreal toads across four developmental life stages in captivity and the wild, ii) pre-metamorphic tadpole skin bacteria before and after reintroduction to the wild, and iii) adult skin bacteria during reintroduction to the wild. We used barcoded amplicon sequencing of the 16S small subunit of the rRNA gene on the Illumina MiSeq platform to characterize the bacterial communities. We demonstrated that differences occur across the skin gut and mouth microbes in captive versus wild boreal toads, and that the degree of difference depend on developmental stage. Skin bacteria from captive versus wild tadpoles were more similar relative to post-metamorphic life stages. When captive reared tadpoles were introduced to a wild site, their skin bacteria changed to mirror wild boreal toads within weeks. Similarly, the microbiome of reintroduced adult boreal toads also shifted to mirror wild-type microbes. Our results indicate that the microbial signature of boreal toads reared in captivity does not persist after release into natural habitat. The relationship between changing microbes and host health is not well understood for the majority of animal species but is an important part of wildlife conservation.