Resting eggs of Ceriodaphnia cornuta can sense predation risk and population crowding signals but cannot distinguish the types of predation risk

Cladocerans can produce dormant stages to avoid unfavorable environments, such as predation pressure and population crowding. However, only a few studies evaluated the influences of the biochemical signals of predation risk and population crowding on the termination of dormant stages of cladocerans. This study aimed to investigate the influences of predation risk signals from different predators and crowding signals from high-density populations on the hatching of cladoceran resting eggs and the anti-predation defensive traits of hatched offspring. We collected resting eggs of Ceriodaphnia cornuta from the surface of lake sediments and incubated them under different biochemical signals (fish kairomones, Chaoborus kairomones, alarm signals, and crowding signals) in the laboratory. In response to fish kairomones, Chaoborus kairomones, and alarm signals, the hatching time of resting eggs was delayed to a certain extent, and the body length of the offspring hatched from resting eggs increased at their birth and decreased at their first reproduction. This indicated that the offspring hatched from C. cornuta resting eggs possibly can sense predation risk signals but cannot distinguish the type of signals. In addition, the effects of crowding signals on the resting eggs were similar to those of fish kairomones, both of which can increase the body length of hatched offspring at birth, but these influences would not be further enhanced in the simultaneous presence of fish kairomones and crowding signals. This study will contribute to a better understanding of the perception of resting eggs to environmental biochemical signals and the corresponding hatching strategies of cladocerans.