[PhD Thesis Public Presentation_C209_ zoom is also available] ‐ Rio Kashimoto– “Genomic and transcriptomic characterization of giant sea anemones: essential partners of an iconic mutualistic symbiosis”

Presenter: Rio Kashimoto

Supervisor: Prof. Vincent Philibert Laudet

Co-supervisor: Prof. Noriyuki Satoh

Unit:Marine Eco-Evo-Devo Unit

Zoom URL: to be available 48 hours prior to the examination

Title:

Genomic and transcriptomic characterization of giant sea anemones: essential partners of an iconic mutualistic symbiosis

Abstract:

The symbiotic relationship between giant sea anemones, photosynthetic algae of the family Symbiodiniaceae, and anemonefish represents a classic example of mutualistic symbiosis within coral reef ecosystems. Despite its significance, the underlying mechanisms of this symbiosis remain incompletely understood. The complex and intricate patterns of associations observed among 28 anemonefish species and 10 giant sea anemone hosts contribute to the challenges and uncertainties involved in accurately identifying the giant anemone species found worldwide.
To address these knowledge gaps, I firstly conducted a transcriptome study focusing on giant anemone species in Okinawa. I elucidated their molecular similarities, phylogenetic relationships, and molecular differences at the transcriptomic level. My data support the presence of three distinct groups corresponding to three genera: Entacmaea, Heteractis, and Stichodactyla. The basal position among the three groups belongs to Entacmaea, which was the first to diverge from a common ancestor. While the magnitude of genetic difference between the representatives of Entacmaea and Stichodactyla is large, intra-specific variation within Stichodactyla is much smaller and seems to result from recent speciation events.
The host preferences of anemonefish species were also investigated. While some anemonefish species known as highly specialized to inhabit only one species of sea anemone (e.g., Amphiprion frenatus with Entacmaea quadricolor), whereas others are more generalist and can live in almost any host species (e.g., Amphiprion clarkii). Notably, previous reports did not mention the host preference of Entacmaea for A. frenatus and A. clarkii. Therefore, a large-scale transcriptomic analysis of giant sea anemones was conducted, using 55 anemone samples collected from anemonefish habitat in Japan (Okinawa main island, Ishigaki, Kerama, Amami (Kagoshima) Shimoda (Shizuoka), Shikine and Ogasawara (Tokyo)) to build a robust phylogeny. With this dataset, I observed that the bubble-tip sea anemone E. quadricolor, currently considered to be a single species, can in fact be separated into at least four distinct cryptic lineages (A-D). Moreover, these lineages can be precisely distinguished by their association with anemonefish: A. frenatus is only found associated with lineage D, whereas A. clarkii lives in the other three lineages.
To further investigate the evolutionary success and adaptation of this symbiosis, the complete genomes of E. quadricolor, H. crispa, and S. gigantea were sequenced. These genomic studies aim to decipher the underlying genomic novelties that have contributed to the adaptation of these species in the context of the symbiotic relationship. Functional experiments, including differential expression analysis (DEG) in the model organism S. gigantea, will be performed to provide additional support for the adaptive effects observed during the symbiosis process with anemonefish.