. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CO2 AND PHOTOPERIODISM 149 The low O2 and high CO2 environment, which occurs normally with aerobic metabolism in a closed system may therefore act independently in breaking the photo-refractory phase of diapause in Daplinia. Presumably this is what happens in a stagnant medium and ultimately results in the disappearance of one of the two inducible phases within the daily cycle of the embryo. Ballarcl and Grant Lipp (1969) have shown that a low O2 atmosphere achieves partially the effect of an elevated CO2 atmosphere in break
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CO2 AND PHOTOPERIODISM 149 The low O2 and high CO2 environment, which occurs normally with aerobic metabolism in a closed system may therefore act independently in breaking the photo-refractory phase of diapause in Daplinia. Presumably this is what happens in a stagnant medium and ultimately results in the disappearance of one of the two inducible phases within the daily cycle of the embryo. Ballarcl and Grant Lipp (1969) have shown that a low O2 atmosphere achieves partially the effect of an elevated CO2 atmosphere in breaking the dormancy of clover seeds. A preliminary exposure to low O2 was not necessary for CO2 effectiveness in their material, how- ever. ACTIVE DURATION A FUNCTION OF GENOTYPE TEMP. OTHER. DURATION FIGURE 8. Schematic model of diapause interval in embryos of Daphnia pulex. Each of four states (A-D) are identified by the changing responsiveness of the embryos to specific stimuli in the environment, including temperature, O3 and CO2 tensions, and light. In a fifth state (E) the embryo is photosensitive. The light requirement for terminating the diapause may differ depending on the manner of entry to the photo-sensitive phase of diapause. (See text for details.) A further complexity is that the Daphnia embryos are not immediately sensitive to the low O2 stimulus. Some interval of incubation in the stream is a necessary preliminary condition for response to low O2 after only two weeks. Four weeks of exposure was indaquate when the embryos were removed from the culture vessel and placed directly in low O2. Preliminary experiments suggest that the embryos become primed for response to the low O2 environment if the flow of medium in the stream is interrupted periodically. Photo-refractoriness in the diapaused embryo may represent a variety of inter- nal states, if responsiveness to the variety of stimuli employed in this and other studies may be used as criteria. A descriptive model (
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
