Agradecimentos: Atlantic Forest Fieldwork was conducted through the "Documenting Threatened Species" project. We thank everyone who helped with fieldwork and lab work on the projects that contributed to this paper. National Science Foundation (DEB-1947681) (CGB), (DEB-2225683) (JP). Fresno Chaffee Zoo Wildlife Conservation Fund (PP). Columbus Zoo Fund for Conservation (PP). Brazilian National Council for Scientific and Technological Development (CNPq #300984/2022-7) (PP) (CNPq #306623/2018-8) (CFBH), (CNPq #302834/2020-6) (LFT). São Paulo Research Foundation (FAPESP #2013/50741-7) (CFBH), (FAPESP #2014/16320-7) (CN) (FAPESP #2016/25358-3; #2019/18335-5) (LFT) Ver menos

Abstract: Microbial diversity positively influences community resilience of the host microbiome. However, extinction risk factors such as habitat specialization, narrow environmental tolerances, and exposure to anthropogenic disturbance may homogenize host-associated microbial communities critical for stress responses including disease defense. In a dataset containing 43 threatened and 90 non-threatened amphibian species across two biodiversity hotspots (Brazil’s Atlantic Forest and Madagascar), we found that threatened host species carried lower skin bacterial diversity, after accounting for key environmental and host factors. The consistency of our findings across continents suggests the broad scale at which low bacteriome diversity may compromise pathogen defenses in species already burdened with the threat of extinction Ver menos