Significance of photoperiodism and diapause control in the multicycle Crustacean Daphnia pulex Leydig

Eukaryote cells traverse the cell cycle, or become growth-arrested at one of two blockpoints, as in an engine of energy conversion. Diapause describes that growth arrest in the cell cycle(s), of single and multicellular individuals. Its temporal position in an annual cycle is an evolved response to the external environment, which is also responsible for sending the necessary signal(s) to receptors in the cell, or to the neural integrator of multicellular individuals.The diapause syndrome, common to protists and Crustacean waterfleas, includes the cell cycle arrest, as well as the induction of mating types, gametogenesis, packaging of the diapaused stage, and the duration of the diapause. The cell-/ life-cycle may be interrupted in a variety of seasonal patterns, which are triggered by one or more identified external signals and are integrated by cell and circadian clocks. Daphnia pulex displays four distinct seasonal patterns of embryonic diapause in four putative genotypes.The ecological implications of diapause in life cycles may be sought in such questions as 1, environmental control of temporal and spatial boundaries in sessile populations; 2, application of knowledge of diapause/dormancy cycles to redesigning ecological communities; and 3, integration of mechanistic and biosystematic approaches in ecology.