Wednesday October 22 2025, 9am (CEST), 8pm (NZST)

Simon K. Davy¹

Inter-partner communication and regulation in the cnidarian-dinoflagellate symbiosis

¹. School of Biological Sciences, Victoria University of Wellington, New Zealand

The cnidarian-dinoflagellate symbiosis is of huge ecological importance as it underpins the success of coral reefs, yet we know very little about how the host cnidarian and its dinoflagellate endosymbionts interact with each other to form a functionally integrated unit, and how biomass of the two partners is regulated to ensure homeostasis and symbiosis stability. Here, I will describe our work with the sea anemone Exaiptasia diaphana (‘Aiptasia’) – a globally-adopted model system for the study of the cnidarian-dinoflagellate symbiosis – aimed at clarifying how the host cnidarian regulates its symbiont population. We focused on symbiont cell-cycle arrest, host apoptosis and autophagy, and symbiont cell expulsion. We measured these in response to both the native symbiont of Aiptasia, Breviolum minutum, as well as several non-native symbiont species - Symbiodinium microadriaticum, Cladocopium goreaui and Durusdinium trenchii - and then applied a range of complex mathematical models to determine the relative importance of the various mechanisms involved. This approach revealed that symbiont cell-cycle arrest is the primary means by which the symbiont population is controlled, though the other mechanisms, and apoptosis especially, all play an important part at different stages of symbiosis establishment and maintenance. Furthermore, while there were commonalities between the responses to the different dinoflagellate species, D. trenchii was notable in that its proliferation was less tightly regulated than the other symbionts and it induced an earlier depression of host apoptosis. This latter is finding is especially interesting given that D. trenchii is known to be an opportunistic, nutritionally selfish partner. I will end the seminar by briefly exploring this latter point, giving an overview of some of my group’s other work, where we apply a range of omics (esp. proteomics and metabolomics), imaging mass spectrometry and immunocytochemistry techniques to understand how the host and symbiont communicate and interact with one another, and how this is impacted by symbiont identity, thereby driving patterns of host-symbiont specificity.