Abstract: Studies of animal and plant microbiomes are burgeoning, but the majority of these focus on bacteria and rarely include micro-eukaryotes other than fungi. However, there is growing evidence that micro-eukaryotes living on and in larger organisms (e.g. plants, animals, macroalgae) are diverse and in many cases abundant. One reason for this neglect is methodological: using PCR primers targeting all eukaryotes on eukaryotic host tissue usually results in an overwhelming proportion of host-derived sequences relative to their symbionts and parasites. Host-blocking primers and metagenomic sequencing now offer viable alternatives to general PCR screens. While many groups of micro-eukaryotic parasites are recognised, myriad other micro-eukaryotes are associated with hosts as previously unknown parasites (often genetically divergent so difficult to amplify using standard PCR primers), opportunistic parasites, and other ecto- and endo-symbionts. These fulfill a wide range of roles from pathogenesis to mutually beneficial symbioses, but mostly their roles are unknown and likely fall somewhere along this spectrum, although with the potential to switch the nature of their interactions with the host under different conditions. This talk will review the current state of play in ‘eukaryome’ studies, present some case studies from aquatic invertebrates and macroalgae, and suggest future trajectories for research in this and related areas.
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