The curious world of brown seaweeds: sex, virus and mating rituals

Brown algae (seaweeds) are remarkable organisms that independently evolved complex multicellularity, making them an invaluable window into how development can arise in very different evolutionary contexts. In this talk, I will explore the biology of these seaweeds, from the molecular mechanisms governing their mating rituals, including sex determination, pheromone signaling, cell-cell recognition and gamete fusion, and the surprising ways in which viruses shape their life cycles. I will highlight our recent discovery of a giant virus that integrates into the genome of the model alga Ectocarpus, reactivating during reproduction and influencing both host development and evolution. Together, these stories reveal brown algae as a powerful system for uncovering fundamental principles of multicellularity, reproduction, and host–virus interactions across the tree of life.