An efficient method for hatching diapausing embryos of Daphnia pulex species complex (Crustacea, Anomopoda)

A general method for efficiently hatching sexually produced diapausing embryos of the microcrustacean Daphnia is valuable for establishing Daphnia as a genetic model system. In this study, we examine the effect of ultraviolet light and different amounts of storage time in darkness on the hatching efficiency in two species of the Daphnia pulex species complex, D. pulex and Daphnia pulicaria. We identified a set of lighting conditions that can trigger 80% to ~100% hatching rate for embryos produced through selfing, outcrossing, and obligate parthenogenesis. Furthermore, we found that a storage time of at least 2 weeks in the dark before exposing embryos to ultraviolet light is critical for achieving high hatching rate. The identification of these key factors for hatching diapausing embryos can greatly facilitate future Daphnia research involving complex breeding designs as well as investigating the genetic switch that activates the hatching of diapausing embryos.