Skin microbiota differs drastically between co-occurring frogs and newts.

Diverse microbial assemblages inhabit amphibian skin and are known to differ among species; however, few studies have analysed these differences in systems that minimize confounding factors, such as season, location or host ecology. We used high-throughput amplicon sequencing to compare cutaneous microbiotas among two ranid frogs (Rana dalmatina, R. temporaria) and four salamandrid newts (Ichthyosaura alpestris, Lissotriton helveticus, L. vulgaris, Triturus cristatus) breeding simultaneously in two ponds near Braunschweig, Germany. We found that bacterial communities differed strongly and consistently between these two distinct amphibian clades. While frogs and newts had similar cutaneous bacterial richness, their bacterial composition strongly differed. Average Jaccard distances between frogs and newts were over 0.5, while between species within these groups distances were only 0.387 and 0.407 for frogs and newts, respectively. At the operational taxonomic unit (OTU) level, 31 taxa exhibited significantly different relative abundances between frogs and newts. This finding suggests that chemical or physical characteristics of these amphibians' mucosal environments provide highly selective conditions for bacterial colonizers. Multi-omics analyses of hosts and their microbiota as well as directed efforts to understand chemical differences in the mucosal environments (e.g. pH), and the specificities of host-produced compounds against potential colonizers will help to better understand this intriguing pattern.