A FIELD-TEST FOR THE CUES OF DIAPAUSE IN A FRESH-WATER COPEPOD

The calanoid Diaptomus sanguineus switches each year in spring from making eggs that hatch immediately to making diapausing eggs that rest in lake sediments for an extended period. In lakes and ponds containing planktivorous fish, the timing of the switch is highly consistent between years and comes at the theoretically optimal time (late March) to avoid intense summer predation. In fishless ponds the timing comes 1-2 mo later. Copepods made immediately hatching eggs under short-day or low-temperature conditions, and diapausing eggs under long days or high temperatures. Similar diapause phenologies are produced by different sensitivities to the environmental cues. -from Authors