Effects of feeding experience in the copepod Eucalanus pileatus: a cinematographic study

Abstract

High-speed microcinematography was used to examine the effects of prior experience with particular cell types on the feeding efficiency of a calanoid copepod. Female Eucalanus pileatus were fed monocultures of either the 5-μm diatom Thalassiosira pseudonana or the 11-μm diatom T. weissflogii during a 2-to 3-d preconditioning period. The smaller diatoms are accumulated passively by the second maxillae while the larger diatoms are detected and actively captured as individual cells. Four females from each preconditioning culture were transferred to a monoculture of the large cells and their behavior filmed at five intervals over a 24-h period to determine whether a loss of efficiency occurs when the copepods must shift capture modes. Ingestion rates for females experienced with the larger cells were approximately 2.5 times higher than those of inexperienced females. Six sequential behavioral steps in the feeding process could alter ingestion rates: (1) amount of time spent flapping the feeding appendages. (2) rate of flapping of the feeding appendages, (3) ability to detect individual cells, (4) success rate of capture attempts, (5) capture and handling time per cell and (6) rejection rate of captured cells. An increased ability to detect cells and a decreased rejection rate contributed significantly to the higher ingestion rate of experienced feeders, indicating that copepods have the ability to learn during the feeding process. Grazing rates may be seriously underestimated in experiments which do not include a preconditioning period, especially those which calculate ingestion over short time intervals. Such effects may also influence the feeding of copepods in the field when encountering changes in particle spectra through vertical migration or horizontal displacement.