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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. [ABSTRACT FROM AUTHOR]

Both predation risk and crowding can induce sexual reproduction in Daphnia, and predator kairomones can also cause population crowding. It is, however, unclear as to whether sexual reproduction is caused by kairomone per se or indirectly by kairomone‐induced crowding.In this study, we cultured Daphnia pulex in the presence of fish kairomone, with newborn offspring being retained (increasing population density) or removed (constant population density). The relationships among fish kairomone, population density, and indicators of sexual reproduction were assessed using structural equation models.The results showed that when offspring were retained in the population, the population density and sexual reproduction by Daphnia simultaneously increased in response to the presence of the fish kairomone, whereas sexual reproduction was not directly affected in the presence of fish kairomones alone. Conversely, when maintaining a constant population density, the number of ephippia and ratio of male to female of Daphnia increased with increasing population density, but the presence of fish kairomone did not promote sexual reproduction. Structural equation model analysis indicated that population density, rather than the fish kairomone, was the significant factor promoting sexual reproduction.The findings of this study indicate that population density directly triggers sexual reproduction in Daphnia populations. Our observations provide new insights into environmentally induced sexual reproduction, and on this basis, we suggest that a more thorough consideration of the interactions among environmental factors in determining sexual reproduction is necessary. [ABSTRACT FROM AUTHOR]

Daphnia can develop a VARIETY of inducible defensive traits when they sense predator kairomone and transmit the predation risk information from females to their offspring. However, limited research has focused on how Daphnia females transmit predation risk information across multiple broods when the mothers and offspring are respectively exposed or not exposed to predation pressure.Here we conducted a prolonged predation risk transmission experiment, where three generations of Daphnia pulex individuals were cultured with or without fish kairomone until they produce six broods of offspring. Life history traits and morphological defensive traits were measured to investigate how inducible defensive traits were transmitted across generations and multiple broods.Our results demonstrated that (1) inducible defensive traits of offspring were mainly determined by the offspring's environment rather than their mothers' experience; and (2) as the mothers produced more broods of offspring, inducible defensive traits of the offspring were gradually increased and then decreased.The present study highlights the reversibility and differences among generations and broods of the transmission of predation risk information via transgenerational effects, which provides a basis for further understanding of transgenerational plasticity across broods. [ABSTRACT FROM AUTHOR]

• Scenedesmus obliquus responded to predation risk and macrophytes allelopathy. • Grazer cues induced stronger colony formation than macrophytes did in S. obliquus. • Macrophytes allelopathically disturbed algal anti-grazer colony formation. • Interference on algal morphological defense was species-specific in macrophyte. • Algal morphology is a sensitive indicator of responding to grazing and allelopathy. Predation and competition are the primary interspecies interactions in aquatic ecosystem. Understanding how these two stressors interactively affect the organisms is critical to predict the food web dynamics. Here, we investigated the responses of the green alga Scenedesmus obliquus to predation risk from zooplankton (Daphnia magna) and to allelopathy from four macrophytes (Cabomba furcate , Nymphoides hydrophylla , Lemna minor and Chara sp.) separately and jointly. Neither the Daphnia -derived cues nor the four macrophyte exudates affected the algal growth rate compared with those in control. Nonetheless, both the two stressors induced the multicelled colony formation in S. obliquus , which was, however, much more strongly induced by the Daphnia cues. In addition, the four macrophytes differentially altered the anti-grazer morphological defense in algae: exudates from Nymphoides and Chara markedly promoted the enhancing effect of Daphnia cues on the eight-celled colonies formation, resulting in the increased number of cells per particle of the algal population. Nonetheless, more four-celled colonies but fewer eight-celled colonies were formed under Lemna exudates exposure, in contrast to the unchanged multicelled colonies growing in Cabomba exudates under Daphnia cues exposure. The results revealed that macrophytes allelopathically disturbed the anti-grazer morphological defense in phytoplankton even though they had no direct impact on algal growth, and this interference was species-specific in macrophyte. As a result, the predator-prey interactions between herbivores and phytoplankton can be potentially changed differently in different macrophyte-dominated freshwaters, contributing to the new cognition of the important role of macrophytes in ecosystem functioning. It suggests that the algal morphology can function as a useful indicator of phytoplankton response to simultaneous stresses from predation and competition. [ABSTRACT FROM AUTHOR]

• Daphnia change morphology and life history under multiple predation cues. • Changes in individual traits caused by predation cues alter population dynamics. • Individual traits affect population dynamics through diverse pathways. • Individual traits affecting population dynamics were variable among different clones. Individual traits responding to predation cues are widespread in many aquatic and terrestrial organisms. However, linking individual traits to population dynamics in response to predation cues is poorly understood despite its important role in shaping ecosystems. In this study, we investigated the individual traits associated with population dynamics of Daphnia mitsukuri in response to two different cues from fish predation. Two clones of D. mitsukuri were reared under alarm signal, kairomone, and their combination treatment until the populations reached maximum abundances. Individual inducible traits, grazing rates, and population parameters were recorded for the growing populations. Our data showed the population dynamics were highly correlated with the individual traits, and some mechanical correlations were discussed in the present study. Specifically, in the combination treatment, the decreased individual size contributed to enhancing the individual grazing rate at a high population density, which ultimately resulted in a higher (75%) maximum population density compared to the control. Besides, diversified links between individual traits and population dynamics were observed in different clones, especially in dormant egg production. In summary, inducible changes in individual morphological characteristics and life history traits were associated with variation in population dynamics of Daphnia in response to cues from predation. This study is helpful to understand the effects of signals of predation risk on the individual and population levels. [ABSTRACT FROM AUTHOR]