Ists capable of eating other protists (eukaryophagy). The ability to ingest

Ists capable of eating other protists (eukaryophagy). The ability to ingest bacteria-scale particles appears to be plesiomorphic among eukaryotes, but only a limited number of eukaryotic clades evolved eukaryophagy. Molecular clocks [25,26] suggest that the ciliates and other eukaryophagic clades radiated during the Neoproterozoic Era, long after the origin of the domain and, indeed, hundreds of millions of years after endosymbiosis led to the evolution of photosynthetic eukaryotes [268]. That eukaryotes rose to ecological prominence as primary producers in the oceans about when eukaryophagic protists radiated suggests a possible relationship between the two events [29,30]. We emphasize, once again, the limited range of our preliminary experiments, but stress that their implications warrant further research. Just as the advent of carnivory gave ecological impetus to Cambrian animal evolution (e.g., [31]), the Neoproterozoic radiation of eukaryophagic protists may have changed phytoplankton growth dynamics in a way that favored the expansion of eukaryotic phytoplankton in the oceans. When small metazoan grazers expanded in the water columns of shelf seas is less clear. Fragmentary cuticular fossils indicate that total-group copepods had already differentiated by the Middle Cambrian Period [32]. Few fossils document the subsequent evolution of copepods [33], but there is a suggestion that the current ecological importance of calanoid copepods in pelagic food webs dates to the Mesozoic Era [34]. Interestingly, the effect of copepod grazers in our experiments was most pronounced in cultures of the diatom T. weissflogii. Copepod grazing was associated with decreased cell size in the diatom population, as well as a 4- to 6-fold increase in Si uptake. Pondevin et al. [35] found that Si uptake by T. weissflogii doubled when grown in media that previously contained diatoms and copepod grazers and interpreted the enhanced Si uptake as an inducible defence. Our results corroborate these results and extend them through the observation that grazing by a ciliate does not induce the same response. Decreases in both mean diatom cell size and silica usage through the Cenozoic Era have been interpreted in terms of biophysical responses to directional changes in the marine environment, especially carbon dioxide and dissolved silica levels in surface oceans [369]. The experimental observation that both parameters change in response to copepod grazers adds nuance to the interpretation of observed evolutionary patterns.Estriol Based on biomechanical analyses, Hamm et al.Vunakizumab [40] hypothesized that the silica frustules of diatoms resist crushing by mandibulate microarthropods such as copepods, and the correlation of silica uptake with the presence or absence of a copepod grazer is consistent with this hypothesis.PMID:23847952 Overall, our experiments document several distinct responses of phytoplankton to ciliate and copepod grazers. In some taxa, including the green algae and diatoms used here, grazing of either type induces a change in growth dynamics. Increased armour is another class of response, apparent in the increased silica uptake by diatoms exposed to copepod grazers and, as well, in the tendency of the dinoflagellate Protoceratium reticulatum to encyst. And toxin synthesis is a third response, effective against the copepod grazers inSynechococcus sp. + A.30 mMSpent medium fromtonsa 1 day cultureSO42SO42SO42SO42 SO42 SO42SO42SO42SO42SO42SO42SO42 SO42 SO42 SO5 mM SO4230 mM.