Diverse swimming behaviors of Cryptophytes

Cryptophytes are aquatic unicellular eukaryotes, or protists, that inhabit both marine and freshwater environments worldwide and whose photosynthetic forms may be important primary producers and prey for higher trophic levels. Cryptophytes have flattened, elliptical cells and swim using two flagella. Swimming in protists is one of their more conspicuous attributes that stimulated early studies on their ecology and taxonomy. In this research work, we investigate the swimming patterns and behaviors of a representative group of cryptophytes having different cell geometries, feeding behaviors, and plastid type and/or presence. We observe swimming cryptophytes using the High-Speed Microscale Imaging System, which allows behavioral evaluations in environments closer to natural conditions, avoiding confinement and heating effects common in traditional microscopy techniques. We have observed various swimming behaviors and speed among the species: helical trajectories with vastly different radii for Rhodomonas salina, Proteomonas sulcata, Chroomonas mesostigmatica, Chilomonas paramecium, Hemiselmis cryptochromatica and Guillardia theta; almost straight paths for Teleaulax amphioxeia; tumbling-like motion for Goniomonas pacifica; and nearly circular trajectories for Storeatula major. These distinct swimming behaviors may affect how cryptophyte species optimize the exploration of their environment depending on their trophic mode and could shape their survival strategies against predatory zooplankters.