Agarophyton vermiculophyllum temperature experiment

Seaweeds are holobionts, meaning they are colonized by a microbial community which is directly linked to their performance. This community is shaped by an interplay of stochastic and deterministic processes. Among deterministic processes are the mechanisms which the host deploys to manipulate the associated microbiota to remain benign or even beneficial toward the host. Seaweeds are under constant attack of marine microbes and deploy mechanisms that, for instance, disturb quorum sensing in fouling bacteria or repelling and attracting harmful and beneficial microbes. However, when the host is exposed to suboptimal or stressful conditions, these mechanisms may well be compromised, ultimately leading to an increase in stochastic processes and potentially a microbial community that is harmful to the host (also termed dysbiosis). The notoriously invasive seaweed Agarophyton vermiculophyllum has spread across the northern hemisphere and thrives in various ecosystems that are characterized by a range of temperatures. In the present study we simulated an invasion event by translocating algae from different populaitons from their natural environment into a common garden. In the experiment, we applied a disturbance and monitored the secondary succession of the microbial community under an optimal and elevated temperature regime. Our aim was to test the implicit hypothesis of the Anna Karenina Principle, which posits that microbial community structure of stressed holobionts is more variable due to a decrease of deterministic processes. We found a substantial increase in beta-diversity at the elevated temperature and a decreased performance of the host. Therefore, our results are in line with the Anna Karenina Principle and corroborate the importance of environmental variables in structuring host associated microbiota by determining microbial pressure.