Structural and functional skin microbiota on cane toads across 16,000 km of invaded range

Chava L Weitzman , Kimberley A Day, Gregory Brown, Karen Gibb, Keith Allen Christian 

Host-associated microbial communities are shaped by environmental availability, host filtering, microbial interactions, and prior pathogen exposure, with connected habitats promoting greater adaptive microbiome potential. Across the invasive range of cane toads, containing expansive disconnects between populations, we found strong spatial variation in skin bacterial communities, including among nearby sites, and high within-site variability in alpha and beta diversity. Communities were moderately unbalanced, with many low-abundance, highly transient taxa likely contributing to instability and divergence among individuals. Despite this variability, we detected persistent core taxa across broad spatial and temporal scales, suggesting potential functional importance, though their ubiquity in the environment versus host selection remains unresolved. Network analyses showed that keystone taxa typically had low abundance and showed little overlap with core members, indicating that core and keystone concepts may capture distinct facets of microbiome structure. Although taxonomic composition varied widely, functional profiles were more similar among sites, consistent with functional redundancy. Neither functional nor taxonomic patterns aligned with climate, invasion history, or host evolutionary change, emphasising the dominant roles of local environments, microbial reservoirs, and individual host movement in shaping cane toad skin microbiomes.