A method for distinguishing subitaneous and diapausing eggs in preserved samples of the Calanoid copepod genus Diaptomus

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Abstract
The current method to distinguish freshwater diaptomid copepod subitaneous eggs from diapausing eggs involves hatching live eggs and cannot be used on preserved eggs. Comparisons of preserved Diaptomus minutus, Diaptomus sanguineus, and Diaptomus spatulocrenatus egg types revealed a space between the chorion and the vitelline membrane in subitaneous eggs that is absent in diapausing eggs. Ratios of subitaneous to diapausing eggs in preserved samples calculated with the presence or absence of the space were regressed on ratios obtained from hatching of live samples (r = 0.97, P < 0.001). With this method, determination of D. minutus egg types in preserved samples from a lake supported the trend in diapausing egg production indicated by cohort data.