The influence of nutrition on the haemoglobin content of Daphnia

Abstract

The blood of pond-living species of Daphnia contains haemoglobin, which often gives the animals a pink or red colour. The quantity of haemoglobin is very variable; a Daphnia species may be colourless, pink or red in different ponds, or in the same pond at different times. Daphnia may gain or lose considerable quantities of haemoglobin in a few days, as a result of decrease or increase in the amount of dissolved oxygen in the water. In the work reported in this thesis, I have found that the haemoglobin content of Daphnia blood is also influenced by the quantity of available food. The number of parthenogenetic young produced was used as an indication of the state of nutrition. Haemoglobin production did not take place in starved animals even with very Itittle oxygen. At low oxygen concentrations an increase in the amount of food added caused an increase in haemoglobin synthesis to a certain maximum value, above which greater quantities of food had no effect. It had been thought that pale Daphnia placed in a water from a pond which contained red Daphnia produce more haemoglobin than in their own water, at the same oxygen concentration. I have found that this is really due to differences in nutrition. It was also thought that the presence of chlorophyll in food caused greater haemoglobin formation, I have shown that pale Daphnia fed on colourless and on green organisms, such as Gonium c ont'd.., and yeast, Chlorella and Prototheca, Chlamydomonas and Polytoma do not produce significantly different amounts of haemoglobin. Equal quantities by weight of Chlamydoraonas and Polytoma were used. I have investigated a number of ponds containing red and colourless Daphnia at different seasons. An estimate of the maximum and minimum oxygen concentration in various ponds was obtained indirectly by finding the oxygen consumption of pond waters in stoppered bottles in light and in darkness. An estimate of the amount of phytoplankton prosent was also obtained by this means. Possible correlations bet ween the haemoglobin content of the Daphnia and the oxygen content and alkalinity of the pond waters, and the seasons, were also studied.