Unveiling the mysteries of phytoplankton life cycles: patterns and opportunities behind complexity

Life cycles of phytoplankton species have been selected over a long evolutionary history and represent a key element for our understanding of their ecology and natural history and for improving our comprehension of ocean functioning. A species can alternate in its life cycle between four distinct major phases: growth, sex, quiescence and cell death. This implies that the population of a phytoplankton species found in any particular water sample will contain cells that undergo different fates, have strong differentiation in physiology and have different functional roles even if they are genetically identical. The factors regulating transitions among the different phases are still largely unknown but have direct impacts on the ecological distribution of species and on their biogeochemical function. Focused research efforts in recent years have begun to reveal emerging patterns in the variability of phytoplankton life cycle traits. This research has relied both on careful observations in culture and at sea and on making use of new genomics- and transcriptomics-based tools. The study of phytoplankton in the context of their life cycle characteristics opens up new opportunities to address fundamental questions about the physiology and cell biology of these important organisms and creates a new evolutionary and ecological framework for defining phytoplankton functional groups.