Digital Holographic microscopy reveals prey-induced changes in swimming behavior of predatory dinoflagellates. Proc Natl Acad Sci USA

Department of Mechanical Engineering, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 11/2007; 104(44):17512-7. DOI: 10.1073/pnas.0704658104
Source: PubMed


The shallow depth of field of conventional microscopy hampers analyses of 3D swimming behavior of fast dinoflagellates, whose motility influences macroassemblages of these cells into often-observed dense "blooms." The present analysis of cinematic digital holographic microscopy data enables simultaneous tracking and characterization of swimming of thousands of cells within dense suspensions. We focus on Karlodinium veneficum and Pfiesteria piscicida, mixotrophic and heterotrophic dinoflagellates, respectively, and their preys. Nearest-neighbor distance analysis shows that predator and prey cells are randomly distributed relative to themselves, but, in mixed culture, each predator clusters around its respective prey. Both dinoflagellate species exhibit complex highly variable swimming behavior as characterized by radius and pitch of helical swimming trajectories and by translational and angular velocity. K. veneficum moves in both left- and right-hand helices, whereas P. piscicida swims only in right-hand helices. When presented with its prey (Storeatula major), the slower K. veneficum reduces its velocity, radius, and pitch but increases its angular velocity, changes that reduce its hydrodynamic signature while still scanning its environment as "a spinning antenna." Conversely, the faster P. piscicida increases its speed, radius, and angular velocity but slightly reduces its pitch when exposed to prey (Rhodomonas sp.), suggesting the preferred predation tactics of an "active hunter."

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    • "For these reasons digital holographic microscopy has found numerous biological tracking applications e.g. tracking of dinoflagellates, algal spores, spermatozoa and trypanosomes [31], [32], [33], [34], [35], [36], [37], [38]. The sizes of these microorganisms range from 4 µm to 25 µm. "
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    • "Nauen and Lauder 2002; Wilga and Launder 2002). The three-dimensional spatial coordinates can also be determined using holographic techniques with laser (Malkiel et al. 2006; Hobson et al., 2000; Sheng et al. 2007). Here, the method is based on the interference between two laser beams: the referent beam is perceived directly by the measurement machine, and the object beam is perceived indirectly by the diffusion of the beam by the object. "
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    • "The real space information can be reconstructed from the acquired holograms by applying the Kreuzer implementation of the Kirchhoff-Helmholtz reconstruction formula [18]. A four-dimensional set of information, consisting of three spatial coordinates and a temporal coordinate, is provided if one acquires a sequence of holograms of moving objects such as swimming microorganisms [19], [20], [21], [22], [23]. For this data one can derive characteristic descriptors for motility of a given species in a semi-automatic way involving user intervention [20], [23] or fully automatic as soon as a reliable ground truth has been established for the system under investigation [24], [25]. "
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