Delicate plasticity: Maladaptive responses to fish predation risk in Daphnia magna caused by sertraline pollution

Inhibitory effects of toxic Dolichospermum flos-aquae and anatoxin-a on inducible defenses of Daphnia magna

Cyanobacterial blooms, resulting from serious eutrophication, can produce various cyanotoxins and severely disrupt aquatic ecosystems. Inducible defenses are adaptive traits developed by prey in response to predation risks. However, the effects of the increasing proportion of cyanobacteria and cyanotoxins produced during cyanobacterial blooms on the inducible defenses of cladocerans, particularly in terms of behavioral defenses, remain unclear. In this study, we selected Daphnia magna and investigated the defensive traits against predation risks by the predator Rhodeus ocellatus under different ratios of cyanobacteria (Dolichospermum flos-aquae) and green algae (Scenedesmus obliquus), as well as varying concentrations of anatoxin-a (ATX), a cyanotoxin. We recorded the inducible defensive traits involving to morphology, behavior, and offspring production of D. magna. Results showed that the body length of D. magna at sexual maturity and the number of offspring in the first brood were significantly reduced by the presence of D. flos-aquae. Moreover, when the proportion of D. flos-aquae reached 75% and 100%, D. magna did not develop to sexual maturity. Furthermore, D. flos-aquae inhibited the formation of inducible behavioral defense of D. magna, with a stronger inhibitory effect as the proportion of D. flos-aquae increased. In this experiment, the effects of ATX on the morphological traits at sexual maturity and offspring production of D. magna were minor, but ATX still had the potential to inhibit the formation of inducible behavioral defense. We confirmed that changes in the proportion of cyanobacteria and green algae as well as the production of ATX by cyanobacteria during cyanobacterial blooms can affect the growth, development, and inducible defensive traits of cladocerans, potentially altering their population dynamics during such events.

Benefits and costs: Understanding the influence of heavy metal pollution on environmental adaptability in Strauchbufo raddei tadpoles through an energy budget perspective

Understanding the impact of environmental pollution on organismal energy budgets is crucial for predicting adaptive responses and potential maladaptation to stressors. However, the regulatory mechanism governing the trade-off between energy intake and consumption remains largely unknown, particularly considering the diverse adaptations influenced by exposure history in realistic field conditions. In the present study, we conducted a simulated field reciprocal transplant experiment to compare the energy budget strategies of Strauchbufo raddei tadpoles exposed to heavy metal. The simulated heavy metal concentrations (0.29 mg/L Cu, 1.17 mg/L Zn, 0.47 mg/L Pb, 0.16 mg/L Cd) mirrored the actual environmental exposure concentrations observed in the field habitat. This allowed for a comparison between tadpoles with parental chronic exposure to heavy metal pollutants in their habitat and those without such exposure. Results revealed that under heavy metal exposure, tadpoles originating from unpolluted areas exhibited heightened vulnerability, characterized by reduced food intake, diminished nutrient absorption, increased metabolism cost, reduced energy reserves, and increased mortality rates. In contrast, tadpoles originating from areas with long-term heavy metal pollution demonstrated adaptive strategies, manifested through adjustments in liver and small intestine phenotypes, optimizing energy allocation, and reducing energy consumption to preserve energy, thus sustaining survival. However, tadpoles from polluted areas exhibited certain maladaptive such as growth inhibition, metabolic suppression, and immune compromise due to heavy metal exposure. In conclusion, while conserving energy consumption has proven to be an effective way to deal with long-term heavy metal stress, it poses a threat to individual survival and population development in the long run.

Declining aqueous calcium and fish predation risk interactively modify the phenotypic plasticity in Daphnia pulex

Aqueous calcium (Ca) decline is threatening freshwater ecosystems worldwide. There are great concerns about the possible ecological consequences of Ca limitation combined with biological pressures like predation. Here we investigated the interactions between Ca restriction and fish predation risk on the phenotypic plasticity in the keystone herbivore Daphnia, together with physiological responses underlying the plastic trait changes. Fish predation risk induced D. pulex to mature earlier and produce more but smaller offspring at adequate Ca. Declining Ca inhibited the expression of defensive traits, with the inhibitive degree showing a linear or threshold-limited dynamic. The presence of predation risk mitigated the negative effect of declining Ca on reducing body size but exacerbated the delay in maturity, indicating a life history trade-off for larger body size rather than the current reproduction in multi-stressed Daphnia. Actin 3-mediated cytoskeleton and AMPK β-mediated energy metabolism were highly correlated with these plastic trait changes. Altered phenotypic plasticity in planktonic animals is expected to trigger many ecological impacts from individual fitness to community structure, thus providing new insights into the mechanisms underlying decreased Ca affecting lake ecosystems.

Changes in Induced-Antipredation Defense Traits and Transcriptome Regulations of Daphnia magna in Response to 5-HT1A Receptor Antagonist

The serotonin signaling system plays a crucial role in regulating the ontogeny of crustaceans. Here, we describe the effects of different concentrations of the 5-hydroxytryptamine 1A receptor antagonist (WAY-100635) on the induced antipredation (Rhodeus ocellatus as the predator), morphological, behavioral, and life-history defenses of Daphnia magna and use transcriptomics to analyze the underlying molecular mechanisms. Our results indicate that exposure to WAY-100635 leads to changes in the expression of different defensive traits in D. magna when faced with fish predation risks. Specifically, as the length of exposure to WAY-100635 increases, high concentrations of WAY-100635 inhibit defensive responses associated with morphological and reproductive activities but promote the immediate negative phototactic behavioral defense of D. magna. This change is related to the underlying mechanism through which WAY-100635 interferes with gene expression of G-protein-coupled GABA receptors by affecting GABBR1 but promotes serotonin receptor signaling and ecdysteroid signaling pathways. In addition, we also find for the first time that fish kairomone can significantly activate the HIF-1α signaling pathway, which may lead to an increase in the rate of immediate movement. These results can help assess the potential impacts of serotonin-disrupting psychotropic drugs on zooplankton in aquatic ecosystems.