Host metabolite production and microbiome dynamics: effects of long-term diatom adaptation to warming

Marine diatoms contribute significantly to global oceanic primary production, constituting ~25% of earth production but are susceptible to the impacts of ocean warming. While organisms' adaptation to rising temperatures may mitigate these impacts, it could also disrupt species interactions, including those between hosts and their microbiomes. In our study, we examined thermal performance and diversity changes in the microbiome of the tropical diatom <i>Chaetoceros tenuissimus</i> after long-term adaptation to ambient (LA) and warming (LW) temperatures. We observed notable shifts in the metabolomic profile, with amino acids accumulating after LW adaptation and sugars accumulating after LA, while lipids content remained unchanged. After LW, the microbiota increased maximum growth rate without changing its temperature optimum. <i>Roseovarius</i> sp. dominated the microbiome community at both LA (49.6%) and LW strains (42.8%) proving a strong partnership. Extinctions were highest under warming occurring in the low-abundant genera, but different partners developed increasing richness, with changes induced in the core microbiome. Short-term warming, however, resulted in decreased richness. Beta diversity was associated with long-term adaptation instead of assay temperature. Our findings align with general plant species association models, suggesting that long-term evolution of mutualisms enhances diversity and strength, particularly under warming in the marine partnership studied here. Our experimental results highlight the importance of examine long-term coevolution of host- microbiome partnerships to improve our understanding of consequences of warming.