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Artificial light at night (ALAN) dramatically alters the natural daily cycle of light and may cause a suite of physiological and behavioral responses of freshwater crustacean Daphnia . Here, we conducted a life table experiment to investigate the effect of different wavelengths [white (L-L, 400-800 nm), red (R, 614 nm), green (G, 527 nm), and blue (B, 447 nm)] and flashing modes [three colors flash alternately (3-Flash), seven colors strobe alternately (7-Strobe)] of ALAN on the development, reproduction, and predator-induced defenses of Daphnia magna . The results showed that G inhibited the development of the body and tail spine of Daphnia at sexual maturity and decreased their reproduction. The 7-Strobe promoted Daphnia to develop a larger eye. There was an interaction between fish kairomones and ALAN, which intensified over time. ALAN enhanced the response of the relative tail spine length to fish kairomone at sexual maturity. In addition, L-L and R inhibited the body length of 10th instar D. magna in response to fish kairomone. Through the hierarchical cluster method, the 3-Flash and B are recommended as friendly artificial lighting to Daphnia . Our results highlight the interference effects of ALAN on Daphnia , which are helpful to assess the potential impact of light pollution on zooplankton.

Calcium decline and cyanobacterial blooms pose a serious threat to the crustacean zooplankton Daphnia, which has a high demand for calcium. In the present study, we exposed two different clones of Daphnia pulex to different combinations of calcium concentrations (0.1, 0.5, 1.0, 5.0, 10.0 mg L -1 ) and food types (100% Chlorella; 80% Chlorella and 20% non-toxic Microcystis; 80% Chlorella and 20% toxic Microcystis) for 16 days, recorded the key life-history traits, and then used an exponential rise function to fit the traits. Results showed toxic Microcystis and low calcium together negatively affected the survival, development, and reproduction of Daphnia. The negative effect of non-toxic Microcystis and low calcium only affected the development and reproduction. The survival time and reproductive performance increased exponentially with increasing calcium concentration and then approached an asymptotic maximum. Both non-toxic and toxic Microcystis reduced the asymptotic maximum of the reproductive performance. The rising rate at which they reached the asymptotes differed significantly among the three food types; i.e., the reproductive performance of Daphnia was affected in a wider range of calcium concentrations under bad food quality. The findings indicated that Microcystis impaired the tolerance of Daphnia to low calcium, which may cause serious consequences in freshwater ecosystems., Competing Interests: Declaration of competing interest The authors declare no actual or potential conflict of interest., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Eutrophication and warming lead to frequent occurrence of cyanobacterial blooms, which significantly impact on zooplankton. Freshwater zooplankton Daphnia adopts two distinct ways of reproduction: asexual (parthenogenetic) reproduction for rapidly reproducing many offspring in favorable environment and sexual reproduction for producing resting eggs as seed bank to survive in harsh environments. Daphnia pulex has worse performance in growth and reproduction under the exposure to toxic cyanobacteria Microcystis aeruginosa and tends to allocate less energy to reproduction in the case of insufficient food. However, the relative reproductive allocation strategy (energy allocation) of D. pulex individuals exposed to toxic M. aeruginosa is still unclear. Here we tested the relative reproductive performance of D. pulex fed on solely Chlorella pyrenoidosa (high quality food) or Chlorella mixed with toxic M. aeruginosa (low quality food), based on the parthenogenetic reproduction (life-history experiments) and sexual reproduction (population experiments). The results showed that under low quality food conditions, D. pulex reproduced fewer offspring which were also smaller and thus led to a reduced absolute output in parthenogenetic reproduction, but produced ephippia in the same size and quantity compared to those cultured under high quality food conditions. However, as the body size of maternal D. pulex cultured under low quality food conditions decreased, the relative reproductive allocation significantly increased in both parthenogenetic and sexual reproduction, compared to those cultured under high quality food conditions. In conclusion, D. pulex tend to allocate relatively more energy to reproduction under Microcystis conditions, which is a reasonable strategy for it to decentralize the risks from low-quality food., Competing Interests: Declaration of competing interest None., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

In aquatic ecosystems, many phytoplankton species have evolved various inducible defense mechanisms against the predation. The expression of these defenses is affected by environmental conditions such as nutrient availability. Here, we investigated the anti-grazer colony formation in Scenedesmus obliquus at different magnesium concentrations (0-7.3 mg L -1  Mg 2+ ) in the presence of zooplankton (Daphnia)-derived infochemicals. Results showed that at adequate Mg 2+ , S. obliquus formed high proportions of multi-celled (e.g., four- and eight-celled) colonies, resulting in significantly increased number of cells per colony in response to Daphnia filtrate. On the other hand, in Mg 2+ -deficient treatment, the proportion of multi-celled colonies decreased, together with reduced algal growth rate and photosynthetic efficiency. Finally, the treatment without Mg 2+ strongly suppressed the formation of large colony (mainly eight-celled colonies), whereas the algal growth rate was comparable to that in Mg 2+ sufficient treatment. Despite the inhibition of colony formation, the time reaching the maximum number of cells per colony was not affected by the Mg 2+ concentration, which generally took three days in all groups. Our results indicate that Mg 2+  deficient/absent environments significantly reduced anti-grazing colony formation but not the algal growth, suggesting strong dependability of this morphological defensive trait to magnesium fluctuation in S. obliquus.

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]

The gut microbiota has been increasingly recognized to regulate host fitness, which in turn is dependent on stability of community structure and composition. Many biotic and abiotic factors have been demonstrated to shape gut microbiota of cladocerans. However, the interactive effects of these variables on cladocerans fitness due to alteration of gut microbiota and their linkage with life history parameters are poorly understood. Here, we investigated the responses of Daphnia magna gut microbiota to the combined effects of toxic Microcystis aeruginos a and high temperature and its associations with fitness. We found that under good food regime, the temperature has no effect on the composition of the gut microbiota, whereas under high proportion of toxic M. aeruginosa and high temperature conditions, D. magna lost their symbionts. High proportion of toxic M. aeruginosa and high temperature had synergistically negative effects on D. magna performance due to altered gut microbiota. The high abundance of symbiotic Comamonadaceae and good food increased D. magna fitness. The present study illustrates that understanding life history strategies in response to multiple stressors related to changes in the gut microbiota diversity and composition requires integrated approaches that incorporate multiple linked traits and tether them to one another. Image 1 • Elevated temperature and toxic Microcystis reduce Daphnia growth and survival. • High temperature and Microcystis reduce Daphnia fitness by altering gut microbiota. • Daphnia fitness was correlated with the abundance of Comamonadaceae and good food. • Life history parameters were linked with the changes in the Daphnia gut microbiota. High temperature and toxic Microcystis aeruginosa reduce Daphnia magna fitness by altering the composition and abundance of its gut microbiota. [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]

The gut microbiota has a crucial role in host physiology and fitness. Host-microbiota relationships can be disrupted by environmental stressors, which further affect host growth and survival. However, the link between host performance and the gut microbiota composition shaped by increasing antibiotic pollution under different food conditions is not clearly understood. In the present study, we used Daphnia magna as a model organism to investigate the interactive effects of diets (Chlorella with or without Microcystis) and antibiotics on its life history traits, gut microbiota alterations, and their relationship. The results showed that poor diet consumption by D. magna at low and high antibiotic concentrations reduced reproduction and survival. Under good diet conditions, the fitness was reduced only at a high antibiotic concentration. Under good diet conditions, high concentration of antibiotics reduced the abundance of Comamonadaceae and increased the abundance of Pseudomonadaceae, whereas under poor diet conditions, both low and high concentrations of antibiotics increased the abundance of Pseudomonadaceae. Performances of life history traits were positively correlated with an increased abundance of Comamonadaceae but were negatively correlated with increased Pseudomonadaceae abundance. The results of this study revealed the interactive effects of diet and antibiotics on D. magna fitness and correlations between bacterial abundance and life history traits, which has important implications for understanding the effects of pollutants on host-microbiota interactions through changes in phenotypes. Unlabelled Image • Environmental stressors can alter host-microbiota relationship. • Diet and antibiotics shaped Daphnia gut microbiota. • Life history traits were correlated with changes in bacterial abundance. • Changes in phenotypes are important to understand host-microbiota interactions. [ABSTRACT FROM AUTHOR]