Author: Cassie Hoepner
Hoepner, Cassie, 2023 Behind anemone lines: using omics to uncover the mechanisms involved in the iconic symbiosis between host sea anemones and anemonefish, Flinders University, College of Science and Engineering
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Anemonefishes and host sea anemones have one of the most well-known and iconic symbiotic relationships. The association between anemonefishes and host sea anemones has existed for at least 12 million years, however, this symbiotic relationship is quite rare, with the 28 different species of anemonefish living symbiotically with only ten out of over 1700 species of sea anemones. Furthermore, it is clear that both host sea anemones and anemonefishes glean significant fitness advantages from their symbiosis, including improved lifespan and potential reproductive success for anemonefishes, and increased nutrients and protection from predators for host sea anemones, however, the mechanism that enables this relationship. i.e., anemonefishes resistance to their toxic host sea anemone, remains unclear. Current research has focused solely on anemonefishes and the potential for their unique mucus layer to provide a form of protection against the toxins in their host sea anemone venom, with very little consideration for the role the host sea anemone itself may play in the establishment of this symbiosis.
This thesis addresses this significant knowledge gap in our understanding of anemonefishes and host sea anemone symbiosis by exploring the relationship through the lens of the host sea anemone, via five research chapters. Through this body of research, I show that host sea anemones provide additional benefits to their anemonefish symbionts. Chapter 2 examined a previous hypothesis that the symbiotic relationship with toxic host sea anemones reduces the susceptibility of anemonefishes to ectoparasites. I found A. ocellaris living in symbiosis with a host sea anemone in the wild in Malaysia have a reduced ectoparasite load, and in an observational study in Malaysia and the Maldives there was no evidence that anemonefishes visited cleaning stations to remove ectoparasites, which provides further evidence that the sea anemone toxins may aid in protecting anemonefishes from ectoparasites. In Chapter 3 I quantified the nematocyte response of the host Entacmaea quadricolor to A. percula mucus. Acclimated and familiar A. percula trigger significantly fewer nematocytes than unacclimated A. percula, however, there are still some nematocytes fired at A. percula mucus while in association with the sea anemone. In chapter 4, I analysed the lipid and glycan profile of A. percula mucus to reveal that no significant change in lipids composition occurred in mucus collected before, during and after association with an E. quadricolor host, during an eight-week experiment. For the first time this work demonstrates a change of glycan profile in A. percula mucus, however this change only occurred after three weeks of association with E. quadricolor, and within 24 hrs of removal from the E. quadricolor anemone the anemonefish mucus layer had largely reverted back to its original glycan profile. Such a delay in the acclimation of the anemonefish mucus layer is unexpected and further study is needed to uncover the initial mechanism used by anemonefishes that enables them to enter the venomous tentacles of host sea anemones while their mucus layer adapts at the glycan level. In chapter 5, I used a proteotranscriptomics approach to reveal a comprehensive profile of the tentacle transcriptome which results in 2,736 proteins being present in venom from the most popular host anemone E. quadricolor. This work revealed that while E. quadricolor tentacles express RNA transcripts for numerous and diverse toxins only 10% of these are encoded as proteins present in the venom and that the venom mostly consists of mostly non-toxin proteins. In the final chapter, chapter 6, I used differential expression analysis to examine the role E. quadricolor itself plays a role in the establishment of their symbiotic relationship with A. percula, by analysing transcript and protein data from samples collected from E. quadricolor before and after hosting with an anemonefish pair. Specifically, I found that neurotoxin tentacle transcripts and venom proteins responsible for membrane damage, pore formation, and paralysis were downregulated during hosting with anemonefish. I also found that both natural venom inhibitor tentacle transcripts and proteins rich in IG-like domains were upregulated in the presence of anemonefish.
Overall, this thesis demonstrates that host sea anemones play a much bigger role in the establishment and maintenance of their symbiosis with anemonefishes than previously thought, and by applying novel techniques to century-old questions, this thesis has redefined the research path to uncovering the mechanisms enabling the symbiotic relationship between host sea anemones and anemonefishes. Future research should consider the role of host sea anemone venom inhibitors as a resistance mechanism in symbiotic anemonefishes.
Keywords: venomics, symbiosis, endosymbioant, nematocytes, mutualism, omics, toxin resistance, venom
Subject: Biological Sciences thesis
Thesis type: Doctor of Philosophy
Completed: 2023
School: College of Science and Engineering
Supervisor: Karen Burke da Silva