Environment and weight class linked to skin microbiome structure of juvenile Eastern hellbenders (Cryptobranchus alleganiensis alleganiensis) in human care

Abstract

Amphibian skin is integral to promoting normal physiological processes in the body and promotes both innate and adaptive immunity against pathogens. The amphibian skin microbiota is comprised of a complex assemblage of microbes and is shaped by internal host characteristics and external influences. Skin disease is a significant source of morbidity and mortality in amphibians, and increasing research has shown that the amphibian skin microbiota is an important component in host health. The Eastern hellbender (Cryptobranchus alleganiensis alleganiensis) is a giant salamander declining in many parts of its range, and captive-rearing programs are important to hellbender recovery efforts. Survival rates of juvenile hellbenders in captive-rearing programs are highly variable, and mortality rates are overall poorly understood. Deceased juvenile hellbenders often present with low body condition and skin abnormalities. To investigate potential links between the skin microbiota and body condition, we collected skin swab samples from 116 juvenile hellbenders and water samples from two holding tanks in a captive-rearing program. We used 16s rRNA gene sequencing to characterize the skin and water microbiota and observed significant differences in the skin microbiota by weight class and tank. The skin microbiota of hellbenders that were housed in tanks in close proximity were generally more similar than those housed physically distant. A single taxa, Parcubacteria, was differentially abundant by weight class only and observed in higher abundance in low weight hellbenders. These results suggest a true association between this taxa and Low weight hellbenders. Additional research is needed to investigate how husbandry factors and potential pathogenic organisms, such as Parcubacteria, impact the skin microbiota of hellbenders and ultimately morbidity and mortality in the species.