Grazer cues induce stealth behavior in marine dinoflagellates

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 108; no. 10; pp. 4030 - 4034
• Main Authors: Selander, Erik, Jakobsen, Hans H., Lombard, Fabien, Kiørboe, Thomas, Chisholm, Sallie W.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 08.03.2011; National Acad Sciences
• Subjects: Alexandrium; Alexandrium tamarense; Biological Sciences; Cells; Chemical ecology; Comparative analysis; Copepoda; Cultured cells; Dinoflagellida - physiology; Earth Sciences; Ecology; Ecology, environment; Ecosystems; Ekologi; Flasks; Hydrodynamics; Inducible defense; Life Sciences; Marine Biology; Nutrient uptake; Oceanography; Phytoplankton; Plankton; Plankton ecology; Predation; Predators; Sciences of the Universe; Shellfish; Speed; Swimming; Velocity
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.1011870108

Chain formation is common among phytoplankton organisms but the underlying reasons and consequences are poorly understood. Here we show that chain formation is strongly impaired by waterborne cues from copepod grazers in the dinoflagellate Alexandrium tamarense. Chains of Alexandrium cells exposed to copepod cues responded by splitting into single cells or shorter chains. Motion analysis revealed significantly lower swimming velocities for single cells compared with chains, with two-to fivefold higher simulated predator encounter rates for two-and four-cell chains, respectively. In addition, the few remaining two-cell chains in grazed treatments were swimming at approximately half the speed of two-cell chains in treatments without grazers, which reduced encounter rates with grazers to values similar to that of single cells. Chain length plasticity and swimming behavior constitute unique mechanisms to reduce encounters with grazers. We argue that dinoflagellates can regulate the balance between motil ity and predator avoidance by adjusting chain length. The high predator encounter rate for motile chains may have contributed to the low prevalence of chain formation in motile phytoplankton compared with in nonmotile phytoplankton where chain formation is more common.