Abstract
Research on the amphibian skin microbiota has focused on identifying bacterial taxa that deter a pathogenic chytrid fungus, and on describing patterns of microbiota variation. However, it remains unclear how environmental variation affects amphibian skin bacterial communities, and whether the overall functional diversity of the amphibian skin microbiota is associated to such variation. We sampled skin microbial communities from one dendrobatoid frog species across an environmental gradient along the Panama Canal, and from three dendrobatoid frog species before and after the onset of the wet season in one site. We found frog skin microbial alpha diversity to be highest in frogs from sites with low soil pH, but no clear effect of the onset of the wet season. However, we found frog skin microbial community structure to be affected by soil pH and the onset of the wet season, which also resulted in a decrease in between-sample variation. Across the sampled frog species, bacterial functional groups changed with the onset of the wet season, with certain bacterial functional groups entirely disappearing and others differing in their relative abundances. In particular, we found the proportion of Bd-inhibitory bacteria to correlate with mean soil pH, and to increase in two of the frog species with the onset of the wet season. Taken together, our results suggest that structure and predicted function of amphibian bacterial skin communities may be influenced by environmental variables such as pH and precipitation, site effects, and host effects.
Highlights
The interactions between vertebrate hosts and their microbial communities have recently become a subject of accrued interest (Caporaso et al, 2010b, 2012; Escalona et al, 2016; Rebollar et al, 2016a), because microbiota may play an important role in animal ecology and evolution
In terms of bacterial community structure, we found the sites with the lowest mean soil pH (Fort Sherman) and highest mean soil pH (Barro Colorado Island) to plot on opposite sides of the ordination, with both intermediate mean soil pH sites (Cerro Ancon and Pipeline Road) in the middle
Out of 2,084 operational taxonomic units (OTUs), we found 33 most significant OTUs best explaining site differences in D. auratus skin bacterial beta diversity (LDA > 3, Figure 2A)
Summary
The interactions between vertebrate hosts and their microbial communities have recently become a subject of accrued interest (Caporaso et al, 2010b, 2012; Escalona et al, 2016; Rebollar et al, 2016a), because microbiota may play an important role in animal ecology and evolution. The skin microbiota are known to vary between host species (Kueneman et al, 2014; Belden et al, 2015; Pollock et al, 2017) and sampling sites (Kueneman et al, 2014; Krynak et al, 2016). It has been suggested that ontogenetic and seasonal changes contribute to variation in the frog skin microbiota (Longo et al, 2015). It is clear that amphibians depend on microbial environmental reservoirs, such as forest soil, to maintain diverse skin microbiota (Fitzpatrick and Allison, 2014; Loudon et al, 2014; Kueneman et al, 2016a)
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