The Influence of Photoperiod on Reproduction and Molting of Daphnia schødleri Sars

Abstract

Laboratory populations of D. schOdleri Sars kept at constant temperatures (5, 13, 21[degree]C) and fed Chlamydomonas reinhardi usually reached higher levels under a long daily photoperiod (16.5 hours) than under shorter ones (7.5, 10.5, 13.5 hours). Animals fed Chlamydomonas and maintained individually were observed to produce more young at a photoperiod of 16.5 hours than at 7.5 hours; this was true both at 13 and 21[degree]C. Growth of the alga without animals at different photoperiods suggested that most or all of the observed differences were due to more available food. Yeast-fed animals responded differently than those fed algae, that is, the production of young was maximal at 7.5 hours; high molting rates were observed for individuals in groups with high rates of mortality.