Effects of oxygen deficiency on survival and glycogen content of Chironomus anthracinus (Diptera, Chironomidae) under laboratory and field conditions

Abstract

Growth and glycogen content of Chironomus anthracinus in Lake Esrom, Denmark was examined during summer stratification in 1992 and 1993 . Simultaneously, effects of oxygen deficiency on glycogen utilization and survival were experimentally studied . The population consisted of almost fullgrown 4th instar larvae in 1992 and 2nd and 3rd instar larvae in 1993 . Growth rate and glycogen content changed as hypolimnetic oxygen deficiency increased . During a 1st phase of stratification dry weight and glycogen content increased (2nd and 3rd instars) or was almost constant (4th instar) but decreased significantly during the following 2nd phase . This change from growth to degrowth and utilization of endogenous glycogen reserves correlated with a change in the thickness of the microxic layer (<0 .2 mg 021 -') above the sediment surface . The layer increased from 2-3 m in phase 1 to 4-5 m in phase 2, and we suggest that this deteriorated the oxygen conditions and resulted in a change in larval energy metabolism from fully aerobic during the 1st phase to partly anaerobic in the 2nd phase . During the 2nd phase larval metabolism was estimated at less than 20% of normoxic rate . Experimental exposure of the larvae to anoxia indicated highly different survival of young larvae (2nd and 3rd instars) and older larvae (large 4th instars) . The mortality of young larvae was 50% after three days in anoxia at 10 °C, whereas only 25% of the older larvae had died after 3-4 weeks under similar conditions . Extending the treatment, however, resulted in increased death rate of the 4th instar larvae with only 10% surviving after seven weeks . The anaerobic metabolism of 4th instar larvae as estimated from glycogen degradation at 10°C was 5% of normoxia in the interval from 0-5 days but 1 .5% in the interval from 20-25 days . It is concluded that survival of C. anthracinus in anoxia is very limited, but traces of oxygen in the environment allowing for faint aerobic metabolism prolong the survival time of the larvae from a few days (2nd and 3rd instars) or a few weeks (4th instar) to probably 3-4 months .

The role of glycogen during the ontogenesis of Chironomus anthracinus (Chironomidae, Diptera)

“…5) . The rate of glycogen degradation during severe oxygen limitations was approximately the same in both species (1 .7 and 1 .5 ug glycogen mg -1 DW d -' in C. plumosus and C. anthracinus, respectively ; Hamburger et al, 1995) . The difference in observed glycogen store at the end of the stratification period might be explained by differences in duration and severeness of the oxygen deficiency period in the two lakes .…”

“…Growth and glycogen degradation throughout the period of summer stratification have been examined in detail in a previous work (Hamburger et al ., 1995) . Briefly, with declining oxygen concentration larval growth rate decreased .…”

“…The difference in observed glycogen store at the end of the stratification period might be explained by differences in duration and severeness of the oxygen deficiency period in the two lakes . Augenfeld (1967) found indications of anoxia during most of the stratification period in Lake Mendota, whereas C. anthracinus can maintain aerobic metabolism during a first phase of the stratification period in Lake Esrom, and has only partly anaerobic metabolism during the remaining two month period (Hamburger et al, 1995) . By combining results from different cohorts it is possible to follow the amount and fate of glycogen throughout one life cycle .…”

“…Growth and glycogen degradation of 4th instar larvae during summer stratification were examined in detail in an earlier work (Hamburger et al, 1995) . Briefly, as oxygen concentrations declined, growth of the larvae was suppressed and the glycogen concentration was at first unchanged but it later decreased significantly to 18-20% of DW at the time of the overturn (Fig .…”

“…Growth end endogenous glycogen conversion in C. anthracinus during the summer stratification in 1992 and 1993 have been described, and from these studies we approximated the rate of energy metabolisms of the larvae (Hamburger et al, 1995) . Further, in an experimental study, the energy production in aerobic and anaerobic metabolism was examined in response to the environmental oxygen concentration (Hamburger et al, 1994) .…”