RESPIRATORY PHYSIOLOGY IN SUMMER DIAPAUSE EMBRYOS OF THE NEUSTONIC COPEPOD ANOMALOCERA-PATERSONI

The respiratory physiology of summer diapausing eggs of the neustonic copepod Anomalocera patersoni, maintained under constant temperature ( 13 degrees C) and light (12 h light:12 h dark) conditions, was charact erized by a bell-shaped curve, with low O-2 uptake levels at the begin ning of dormancy. This was followed by a steady rise in O-2 consumptio n with maximum levels of 0.002 mu l O-2 embryo(-1) h(-1) 70 d after sp awning. A slow diminution in O-2 uptake then occurred until Day 150 wh en minimum values of 0.0003 mu l O-2 embryo(-1) h(-1) were recorded, c oinciding with the hatching of the first embryos. Embryos continued to hatch asynchronously up to 360 d from the moment of egg laying. When eggs were subjected to 20 degrees C, the respiratory activity was almo st three times higher than at 13 degrees C, even though both re spirat ory curves were similar. The elevated metabolism in eggs kept at 20 de grees C led to death of the embryos possibly due to a total depletion of metabolic reserves. ATP content also differed at the two temperatur es. Diapause eggs kept at 20 degrees C showed no rapid rise in ATP con tent as opposed to those kept at 13 degrees C. The results of temperat ure shock experiments, in which eggs were first kept at winter tempera tures for several weeks, after which the temperature was raised to 20 degrees C for another number of weeks prior to a second period of chil ling at 13 degrees C, showed that as long as embryos were kept at 20 d egrees C no hatching occurred. By contrast, hatching was observed afte r 10 d following the resumption of winter tempera tures, suggesting th at low environmental temperatures are an essential prerequisite for ha tching of these eggs. The type of diapause in A. patersoni differs con siderably from the one described in insects and in another neustonic c opepod, Pontella mediterrana. In this case, there is a U-shaped respir atory curve With greatest O-2 consumption prior to the onset or upon b reaking of diapause. Differences in the two types of diapause seem to involve not only differences in 02 consumption levels but also in the sequence of metabolic changes with time and the metabolic requirements during summer and winter dormancy.