Studying <Emphasis Type="Italic">Daphnia</Emphasis> feeding behavior as a black box: a novel electrochemical approach |
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Authors: | D C Peñalva-Arana P A Moore B A Feinberg J DeWall J R Strickler |
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Institution: | (1) Department of Biological Sciences, Great Lakes WATER Institute, University Wisconsin, Milwaukee, WI 53204, USA;(2) Department of Biological Sciences, Laboratory for Sensory Ecology, Bowling Green State University, Bowling Green, OH 43403, USA;(3) Department of Chemistry & Biochemistry, University of Wisconsin, Milwaukee, WI 53201, USA |
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Abstract: | We present a novel approach for examining the complex feeding behavior of a filter feeder at a previously unexploited scale.
A Daphnia lives in a viscous environment and thus creates a feeding current with a distinct laminar inflow and a repetitive pulsed
outflow. We propose that by treating the feeding apparatus as a black box, and using the pulsed outflow current as a surrogate
to the inside working of the apparatus, we can calculate feeding rate in near real time. The structure of the outflow is interpreted
as a direct representation of the organism’s response to its environment. Therefore, we examine how the work performed by
an organism’s feeding apparatus is altered according to environmental factors and metabolic demands. Our approach is an integration
of optical (Schlieren system) and electrochemical (chronoamperometry) techniques that allow for real time visualization and
temporal analysis of flow systems, respectively. As electrochemistry requires a tracer chemical, we employed low dopamine
concentrations (≤ 1mM), and tested the effect of dopamine on the heart rate and swimming of Daphnia. It appears that dopamine free in solution at concentrations below 10 mM has no adverse effects on the organism, and all
observed differences in Daphnia feeding behavior were due to environmental or metabolic factors. The feeding nature of daphnids in the presence or absence
of food, and differences between the sexes is reported. Our results indicate that in the absence of food a Daphnia has a strict and repetitive feeding behavior with short delays between pumping actions. However, in the presence of food
this behavior becomes complex, with increased delays between pumps, perhaps designed to maximize feeding efficiency. Our observations
demonstrate that males have a higher appendage beat frequency than females under identical conditions. We hypothesize that
the difference may be dictated by metabolic demand, as a male spends more time actively seeking a mate. The application of
electrochemistry to the study of Daphnia feeding behavior is an improvement over current methods for its near real time quantification of behavioral response, its
versatile application under varying environmental conditions and its extreme sensitivity to changes in the organism’s feeding
behavior. This technique is a valuable addition to the current tools available for studying Daphnia feeding behavior and will allow us to learn more about the interactions of an organism with its environment.
Guest editor: Piet Spaak
Cladocera: Proceedings of the 7th International Symposium on Cladocera |
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Keywords: | Daphnia Feeding rate Heart rate Physiology Electrochemistry |
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