Effects of environmental setting and diet on the gut microbial ecology of eastern hellbenders (Cryptobranchus alleganiensis alleganiensis)

Eastern hellbenders (Cryptobranchus alleganiensis alleganiensis) have undergone substantial population declines throughout their range, leading them to become the focus of increased conservation efforts, including care in zoo and university settings. However, effective implementation of such conservation strategies often relies on a comprehensive understanding of host health, which can be directly influenced by the gut microbiome, yet characterization of gut microbiota often remains overlooked in ex situ conservation facilities. Additionally, effects on the gut microbiome associated with releasing zoo-reared animals into the wild are poorly understood. Therefore, these circumstances make hellbenders an ideal species to examine the relationship between zoo management strategies and gut microbial dynamics. 16S rRNA sequencing was used to investigate dissimilarities between the gut microbiome of hellbenders in zoo and wild settings and to evaluate the impact of implementing a wild diet in zoo-reared hellbenders. Additionally, the bacterial composition of zoo-released individuals and wild resident hellbenders was compared to examine the response of the gut microbiome upon release into natural habitat. Selected samples were also chosen for ITS1 rDNA sequencing as a preliminary investigation of the hellbender gut mycobiome. Human rearing strongly affected the gut microbiome, leading to reduced bacterial richness as well as differing community structure than wild hellbenders. However, implementation of a wild diet in a zoo setting modulated the microbiome and appeared to be mainly driven by bacterial turnover. Additionally, both bacterial and fungal gut assemblages demonstrated the capacity for restructuring upon release into native habitat to become more reflective of a wild-type microbiome. We completed the first study elucidating the gut microbial composition patterns of hellbenders, across both zoo and wild settings. These results provide an understanding of the potential impacts of conservation populations in zoos on gut microbial communities and also inform headstart programs of the transition of the gut microbiome post-reintroduction to the wild.