Abstract. The water fleas of the gender of Daphnia are challenged by both, sudden and long-term changes, in oxygen availability within their natural habitats.
Physiological responses of Hb-poor and Hb-rich Daphnia pulex to sudden hypoxia Jens Allmer, Matthias D. Seidl, Ralph Pirow, Rüdiger J. Paul Institute for animal physiology, Hindenburgplatz 55, 48143 Münster
Abstract The water fleas of the gender of Daphnia are challenged by both, sudden and long-term changes, in oxygen availability within their natural habitats. Several different mechanisms evolved as responses to these stresses. Daphnia magna and D. pulex, for example, produce hemoglobin (HB) to increase their oxygen uptake. This mechanism can only cope with longterm changes in oxygen partial pressure since it takes time to synthesize large amounts of this respiratory protein. Sudden changes are regulated by increasing heart and appendage beat rates (Paul RJ et al 1997 J Comp Physiol 167:247). Former studies (Multimessplatz by Pirow et al.) introduced a method enabling us to measure several parameters, namely heart and appendage beat rates, hemoglobin saturation, NADH fluorescence and oxygen partial pressure, at the same time. The setup has been revised and somewhat advanced. It now features a new CCD-Line for measuring of hemoglobin saturation. A software for this camera was designed which calculates HB saturation based on linear regression (Pirow et al 1999 J Exp Biol 202 (22)). Daphnia pulex adapted to low oxygen partial pressure containing high amounts of hemoglobin and therefore appearing red (for simplicity called "reds") were measured. Comparative studies with D. pulex adapted to normoxy (called "pales") were carried out using the same setup. Responses in heartbeat rate are quite similar in reds and pales. Whereas pales do not seem to be able to adjust their appendage beat rates as reds can. HB saturation declines sooner and faster among pales then within reds. Overall changes in NADH fluorescence intensity is higher within the group of pales. Whereas its increase over time is similar within both groups. Known data for Daphnia magna will be compared to newly acquired data concerning Daphnia pulex. The results will be discussed. As will the limitations of our method. We kindly thank "Deutsche Forschungsgemeinschaft" (DFG) for supporting our study.
