The temperature-size rule proposes there is a negative relationship between the size (volume) of an ectothermic organism and the environmental temperature experienced during its development. We question how to validate this hypothesis for the particular case of protozoans because in these unicellular organisms body volume is directly related to the consumption of prey and, on most occasions, the true volume of the cell is unknown. In our opinion, to approach this question, the actual size of the protozoan should be measured when prey are fully digested. To prove our arguments, we designed a series of experiments with the heterotrophic dinoflagellate <em>Oxyrrhis marina</em>, including functional and numerical responses, estimation of the protozoan volume during starvation, and time-dependent acclimation responses. We found that after the digestion of the prey, the size of <em>Oxyrrhis marina</em> was the same regardless of the temperature. We believe that the previous reports on the temperature-size rule using protozoans that show important cellular volume changes because of feeding are biased by imbalances between ingestion and digestion of prey. These imbalances disappear after sufficient acclimation.

Primary Presenter: Albert Calbet, Institut de Ciències del Mar - CSIC (acalbet@icm.csic.es)

Authors:

Albert Calbet, Institut de Ciències del Mar, CSIC  (acalbet@icm.csic.es)

Enric Saiz, Institut de Ciències del Mar, CSIC  (enric@icm.csic.es)