Fig. 1

The impact of single infections on α- and ß-diversity of the host’s microbiome with examples. A Single infections can have a directional effect on microbial species diversity. Equine gut microbial α-diversity, for instance, decreased following helminth infection [17]. B Single infections may result in deterministic changes to the microbial community composition (i.e., ß-diversity), which are characterized by a shift of the centroid (= black dot; e.g., analysed by Permutational Multivariate Analysis of Variance, Permanova). In this case, the dispersion stays similar (e.g. analysed by Permutational Analysis of Multivariate Dispersions, Permdisp). For example, the gut microbial composition shifted in Adenovirus-infected mouse lemurs [11]. C Alternatively, single infections may lead to a changed dispersion, which can be visualized as distance to centroid (spread = black arrow). An example are chimpanzees infected by the simian immunodeficiency virus, which had a more dispersed gut microbiome [21]. D Single infections can also lead to both stochastic and deterministic effects. Three-spined stickleback (Gasterosteus aculeatus), for instance, infected with the cestode Schistocephalus solidus had a more dispersed and shifted gut microbial community [22]. * = significant differences (i.e., p-value < 0.05); ns = non-significant differences (i.e., p-value > 0.05)