Shauna Corr1,2, Mahasweta Saha1, Ruth L. Airs1, Chris D. Lowe2, and Michiel Vos2
1Plymouth Marine Laboratory, Prospect Place, Plymouth, PL1 3DH, United Kingdom
2College of Medicine and Health, University of Exeter, Environment and Sustainability Institute, Penryn, TR10 9FE, United Kingdom
Macroalgae are host to a wide variety of bacteria with which they form chemically mediated relationships, operating as a unified holobiont. Host fitness is often reliant on this symbiosis, with interactions from epiphytic bacteria necessary for the correct physiological functioning, health, development, and resilience of the seaweed. As macroalgae are dominant habitat formers providing a plethora of ecosystem services and commercial benefits, understanding these interactions and how they affect host condition and viability is important not just for macroalgal health, but wider ecosystem and economic functioning. To enhance fitness, seaweeds create a strong selective pressure over the settlement of their microbial community through their chemical structure and metabolites, possibly creating species-specific ecological niches. However, whilst many studies have investigated how algal-bacterial associations shift between species and location, they have not deliberately investigated whether microbial communities are locally adapted. To resolve this question reciprocal transplants via a novel isolation strategy were conducted to test whether a sympatric or allopatric host environment conferred a greater fitness advantage for host associated epibacteria. Transplants were performed on two seaweed species native to Plymouth Sound (UK), Palmaria palmata and Fucus serratus. Results depicted higher fitness for Palmaria palmata isolates in sympatric over allopatric environments, whilst Fucus serratus isolates exhibited no difference in fitness between seaweeds. Results confirm that macroalgae may structure their epibacterial community through chemical selection causing epibacteria to become locally adapted. Nevertheless, this ability is variable between species and may be a consequence of differences in epibacterial diversity, chemical structure, and exuded metabolites.