1986, Strom 2001). A study on strictly heterotrophic protozoa found that light strongly enhanced food body digestion in the dinoflagellate Noctiluca scintillans, and that light had a positive influence on growth and survival in the ciliate Coxliella sp. (Strom 2001). In our experiments, Esoptrodinium cells with multiple large

food bodies appeared qualitatively more common in darkness than in light, suggesting a potential reduced ability to properly digest food bodies in darkness. Second, Esoptrodinium may require light due to a diurnal influence on some Gefitinib clinical trial other aspect of feeding or life cycle (presumably the eyespot of Esoptrodinium is photoactive). A strictly heterotrophic Crypthecodinium sp. dinoflagellate was reported to feed and divide as a population in synchrony with the light:dark cycle, but it was unknown if this was due to a predator or microalgal prey cell response (Ucko et al. 1997). Esoptrodinium appeared equally capable of detecting and ingesting prey in darkness Selleck NVP-AUY922 versus light based on quantification of dinoflagellate cells containing prey-replete food vacuoles between treatments, but the effect of light on the life cycle was not explicitly observed in this study. Third, it remains possible that some unknown labile metabolite produced only by photosynthetically

active prey cells is required for growth by Esoptrodinium. This could have indirectly made it

appear that Esoptrodinium required light to grow, since prey cell photosynthesis ceases in dark treatments. This hypothesis has support in our observation that no nonphotosynthetic prey type tested so far has permitted long-term culture growth of Esoptrodinium. Likewise, Esoptrodinium may require transient light-induced production of some growth factor by ingested prey chloroplasts prior to digestion, e.g., as temporary “kleptochloroplasts” (Schnepf and Elbrächter 1992, Skovgaard 1998). Each of these hypotheses requires further study to be excluded. Mixotrophy is a common strategy in both marine and freshwater dinoflagellates (Stoecker 1999, Hansen 2011), although it is more often assumed than proven. The only evidence 上海皓元 supporting mixotrophy in many chloroplast-bearing dinoflagellates is observation of apparent food bodies in cells, a good indication of mixotrophy but not definitive proof (Schnepf and Elbrächter 1992). Although many freshwater dinoflagellates are qualitatively known or thought to be mixotrophic (Pfiester and Lynch 1980, Schnepf et al. 1989, Fields and Rhodes 1991, Wilcox and Wedemayer 1991, Stoecker 1999, Calado et al. 2006, Hansen et al. 2007), to our knowledge this study makes Esoptrodinium the first taxon of freshwater dinoflagellates to be directly demonstrated to be mixotrophic through quantitative methods.