The Contribution of Hemoglobin to Oxygen Transport in the Microcrustacean Daphnia Magna

Abstract

Problems of oxygen transport in microscopic organisms have been largely approached by theoretical considerations and diffusion models which have permitted the calculation of critical ambient oxygen concentrations, penetration depths for oxygen, and critical body sizes. Such models provide valuable estimates when applied to unicellular organisms and early ontogenetic stages of metazoans such as eggs or embryos. However, fully developed small-sized animals of the advanced phyla are much more complex in anatomy, and their body forms often deviate from simple geometrical shapes. In addition, the presence of circulatory systems requires consideration of internal convective processes as well, which renders the theoretical approach much more difficult. To incorporate circulatory oxygen transport into a theoretical model, it is essential to have some knowledge of the circulatory architecture as well as information on key parameters such as perfusion rate, oxygen tension, and the concentration and oxygen-saturation of the blood oxygen carrier. In the past, small body size represented an almost insurmountable experimental obstacle which hampered the attempt to obtain adequate physiological information. Fortunately, with the advent of digital image processing and advanced optical techniques, expanding the methodical versatility of microscopy, it has become possible to gain this information from those animals which are distinguished by a high level of transparency.