Abstract
Most animals co-exist with diverse host-associated microbial organisms that often form complex communities varying between individuals, habitats, species and higher taxonomic levels. Factors driving variation in the diversity of host-associated microbes are complex and still poorly understood. Here, we describe the bacterial composition of field-collected Hydra, a freshwater cnidarian that forms stable associations with microbial species in the laboratory and displays complex interactions with components of the microbiota. We sampled Hydra polyps from 21 Central European water bodies and identified bacterial taxa through 16S rRNA sequencing. We asked whether diversity and taxonomic composition of host-associated bacteria depends on sampling location, habitat type, host species or host reproductive mode (sexual vs. asexual). Bacterial diversity was most strongly explained by sampling location, suggesting that the source environment plays an important role in the assembly of bacterial communities associated with Hydra polyps. We also found significant differences between host species in their bacterial composition that partly mirrored variations observed in lab strains. Furthermore, we detected a minor effect of host reproductive mode on bacterial diversity. Overall, our results suggest that extrinsic (habitat identity) factors predict the diversity of host-associated bacterial communities more strongly than intrinsic (species identity) factors, however, only a combination of both factors determines microbiota composition in Hydra.
Highlights
The microbial organisms that animals coexist with [collectively known as the host associated microbiota (Berg et al, 2020)] have an increasingly recognized effect on their host (McFall-Ngai et al, 2013)
The results showed that environmental factors were most strongly associated with changes in the microbial community while the bacterial communities still reflect the host species
We investigated factors associated with changes in taxonomic diversity of host-associated microbes in three species of freshwater Hydra (Hydra oligactis, H. vulgaris and H. circumcincta) coexisting in Central European water bodies
Summary
The microbial organisms that animals coexist with [collectively known as the host associated microbiota (Berg et al, 2020)] have an increasingly recognized effect on their host (McFall-Ngai et al, 2013). The microbiota often influences host health (Shreiner et al, 2015; Rathje et al, 2020), behavior (Murillo-Rincon et al, 2017; Vuong et al, 2017), and in some cases it was shown to affect. Diversity affects the number and type of interactions that can be present in a microbial community (Coyte et al, 2015) and influence tripartite interactions between the host, microbiota and pathogens (Fraune et al, 2015; Harrison et al, 2019). Diversity can affect the stability of microbial communities and their resilience to perturbation (Vieira-Silva et al, 2016) and reduction in diversity often leads to dysbiosis in response to environmental stressors or host diet changes (Infante-Villamil et al, 2020). Understanding the factors that determine microbial diversity in natural populations is key to explain variation in host physiology
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