Response Of Daphnia Research Articles

MicroRNA miR-210 Modulates the Water Flea Daphnia magna Response to Cyanobacterial Toxicity.

As a key form of post-transcriptional regulation, microRNAs (miRNAs) regulate gene expression by binding to target mRNAs, leading to mRNA decay or translational repression. Recently, the role of miRNAs in the response of aquatic organisms to environmental stressors has emerged. Daphnia, widely distributed cladocerans, play a crucial role in aquatic ecosystems. Cyanobacterial blooms often cause Daphnia populations to decrease, thereby disrupting ecosystem functionality and water quality. However, the post-transcriptional mechanisms behind Daphnia's response to toxic cyanobacteria are insufficiently understood. This study investigated the role of miR-210, a multifunctional miRNA involved in stress response and toxicity pathways, and its target genes (MLH3, CDHR5, and HYOU1) in two Daphnia magna clones exposed to toxic Microcystis aeruginosa. Results showed that M. aeruginosa inhibited somatic growth rates, led to microcystin accumulation, caused abnormal ultrastructural alterations in the digestive tract, and induced DNA damage in both clones. Notably, exposure significantly increased miR-210 expression and decreased the expression of its target genes compared with the controls. We identified miR-210s regulation on clonal-tolerance variations in D. magna to M. aeruginosa, emphasizing miRNAs' contribution to adaptive responses. Our work uncovered a novel post-transcriptional mechanism of cyanobacterial impact on zooplankton and provided essential insights for assessing cyanobacterial toxicity risks.

Rearing and Experimental Uses of Daphnia: Controlling Animal Nutrition and Assessing Lifespan and Life-History Traits.

Caloric restriction has been found to extend the lifespan of many organisms including mammals and other vertebrates. With lifespans exceeding months to years, age-related experiments involving fish and mammals can be overtly costly, both in terms of time and funding. The freshwater crustacean, Daphnia, has a relatively short lifespan (∼50 to 100 days), which makes it a cost-effective alternative animal model for longevity and aging studies. Besides age-specific mortality, there are a suite of physiological responses connected to "healthspan" that can be tracked as these animals age including growth, reproduction, and metabolic rates. These responses can be complemented by assessment of molecular and cellular processes connected to aging and health. Lifespan and metabolism of this model organism is responsive to long studied modulators of aging, such as rearing temperature and nutritional manipulation, but also pharmacological agents that target aging, e.g., rapamycin, which adds to its usefulness as a model organism. Here we describe how to culture Daphnia for aging experiments including maintaining laboratory populations of Daphnia mothers, growing algal food, and manipulating nutrition of these animals. In addition, we provide methods for tracking common physiological and longevity responses of Daphnia. This protocol provides researchers planning to use this model organism with methods to establish and maintain Daphnia populations and to standardize their experimental approaches. © 2024 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Culturing algae for Daphnia food Basic Protocol 2: General methods for culturing Daphnia Basic Protocol 3: Standardizing and controlling nutrition for experimental Daphnia Basic Protocol 4: Monitoring Daphnia lifespan Basic Protocol 5: Evaluating Daphnia health: Heart rate and respiration, body mass and growth rates, and reproduction.

Combined effects of spinetoram and Microcystis aeruginosa on Daphnia pulex offspring: Maternal effects and multigenerational implications

The increasing occurrence of harmful algal blooms (HABs) in freshwater ecosystems detrimentally affect global water environments. Zooplankton's role in controlling HABs is hindered by contaminant exposure, necessitating research into combined stressors' ecological impacts. The response of Daphnia, a freshwater keystone species, to environmental stressors can be influenced by its maternal effects. Here, we investigated the combined effects of the world-widely used insecticide spinetoram and non-toxic HABs species Microcystis aeruginosa on the life-history traits of D. pulex offspring produced from different maternal food conditions. Four maternal groups were established, with each group receiving a specific blend of C. vulgaris (Ch) and M. aeruginosa (Ma) in varying proportions: A (100% Ch), B (90% Ch + 10% Ma), C (80% Ch + 20% Ma), and D (70% Ch + 30% Ma). The offspring from the third brood were gathered, and a 21-day experiment was carried out, involving various feeding groups (AA, AD, BA, BB, CA, CC, DA, and DD). Results demonstrated that grazing on M. aeruginosa by D. pulex induced maternal effects on their offspring, with the continuous exposure group showing an enhanced tolerance to M. aeruginosa. This study also unveiled that spinetoram could interfere with the molting of D. pulex, leading to developmental retardation. The Recovery Group exhibited an intriguing phenomenon: under the influence of both concentrations of the pesticide spinetoram (0.18, 0.35 μg L−1), D. pulex produced more offspring. This might be due to a combined strategy of allocating more energy towards reproduction in response to low-quality food and a potential hormetic effect from low concentrations of spinetoram. Assessing the interplay of combined stressors across multiple generations, encompassing harmful algal blooms (HABs) and environmental pollutants, is essential for predicting population responses to evolving environmental conditions. This understanding is vital for the protection and management of aquatic environments and ecosystems.

History of exposure to copper influences transgenerational gene expression responses in Daphnia magna

ABSTRACT The establishment of transgenerational effects following chemical exposure is a powerful phenomenon, capable of modulating ecosystem health beyond exposure periods. This study assessed the transgenerational effects occurring due to copper exposure in the invertebrate D. magna at the transcriptional level, while evaluating the role of exposure history on such responses. Thus, daphnids acclimated for several generations in a copper vs. clean medium were then exposed for one generation (F0) to this metal, and monitored for the following non-exposed generations (F1, F2 and F3). Organisms differing in exposure histories showed remarkably different transcriptional profiles at the F0, with naïve organisms being more profoundly affected. These trends were confirmed for F3 treatments, which presented different transcriptional patterns for genes involved in detoxification, oxidative stress, DNA damage repair, circadian clock functioning and epigenetic regulation. Furthermore, regardless of exposure history, a great number of histone modifier genes were always found transcriptionally altered, thus suggesting the involvement of histone modifications in the response of Daphnia to metal exposure. Lastly, remarkably distinct transgenerational transcriptional responses were found between naïve and non-naïve organisms, thereby highlighting the influence of exposure history on gene expression and confirming the capacity of metals to determine transgenerational transcriptional effects across non-exposed generations.

Cyanobacterial effects on an aquatic keystone grazer are reshaped by presence of the herbicide atrazine

Abstract As cyanobacterial blooms and herbicide pollution, which are often detected in eutrophic waters, can separately jeopardise zooplankton populations, there is an urgent and on‐going need to understand the strength and direction of their interactive effects. This is a crucial step toward realistic risk‐evaluation of agricultural pollution in eutrophic waterbodies. In this study, we evaluated how the herbicide, atrazine (ATZ), alters the effects of cyanobacterial food on the zooplankter, Daphnia magna. We found survival time of Daphnia decreased with increasing amounts of Microcystis in their diets, and the magnitude of this cyanobacterial effect was independent of ATZ. In contrast, ATZ exposure triggered faster growth and larger body size in Daphnia fed diets containing Microcystis compared to those fed the good‐food diet. Although toxic Microcystis reduced the overall reproductive output of Daphnia, the presence of ATZ, regardless of the type of food treatment, exhibited a masking effect by further significantly decreasing Daphnia's overall reproductive output, resulting in a low level of reproduction. Finally, we found an expression trade‐off at the molecular scale between growth and reproduction genes on one side, and antioxidation gene on the other, which could account in part for ATZ's influence on Microcystis toxicity to Daphnia at maturation stage. These results demonstrated that ATZ can reshape Daphnia's responses to Microcystis, predominantly with effects on growth and reproductive traits. These trait‐dependent responses were found to be closely linked to the regulation of key metabolic pathways. Collectively, our study enhances current knowledge regarding the potential interaction between fundamental trophic levels in cyanobacteria‐dominated lakes around farmlands, and is helpful to achieve more realistic environmental risk management of agricultural pollution in eutrophic waterbodies.

Environmental transcriptomics under heat stress: Can environmental RNA reveal changes in gene expression of aquatic organisms?

To safeguard biodiversity in a changing climate, taxonomic information about species turnover and insights into the health of organisms are required. Environmental DNA approaches are increasingly used for species identification, but cannot provide functional insights. Transcriptomic methods reveal the physiological states of macroorganisms, but are currently species-specific and require tissue sampling or animal sacrifice, making community-wide assessments challenging. Here, we test whether broad functional information (expression level of the transcribed genes) can be harnessed from environmental RNA (eRNA), which includes extra-organismal RNA from macroorganisms along with whole microorganisms. We exposed Daphnia pulex as well as phytoplankton prey and microorganism colonizers to control (20°C) and heat stress (28°C) conditions for 7 days. We sequenced eRNA from tank water (after complete removal of Daphnia) as well as RNA from Daphnia tissue, enabling comparisons of extra-organismal and organismal RNA-based gene expression profiles. Both RNA types detected similar heat stress responses of Daphnia. Using eRNA, we identified 32 Daphnia genes to be differentially expressed following heat stress. Of these, 17 were also differentially expressed and exhibited similar levels of relative expression in organismal RNA. In addition to the extra-organismal Daphnia response, eRNA detected community-wide heat stress responses consisting of distinct functional profiles and 121 differentially expressed genes across eight taxa. Our study demonstrates that environmental transcriptomics based on extra-organismal eRNA can noninvasively reveal gene expression responses of macroorganisms following environmental changes, with broad potential implications for the biomonitoring of health across the trophic chain.

Selective ingestion and response by Daphnia magna to environmental challenges of microplastics

Our current understandings of the effects of microplastics and nanoplastics (MNPs) on aquatic animals are predominantly based on the single types of plastic particles. In the present study, we employed the highly fluorescent MNPs that incorporated aggregation-induced emission fluorogens and investigated the selective ingestion and response of Daphnia exposed to different types of plastics at environmentally relevant concentrations simultaneously. When daphnids were exposed to a single MNP, D. magna ingested them instantly in significant amounts. However, even low concentrations of algae had a significant negative impact on the MNP uptake. Specifically, algae caused the MPs to pass through the gut faster, reduced acidification and esterase activity, and changed the distribution of MPs in the gut. In addition, we also quantified the influences of size and surface charge on the selectivity of D. magna. The daphnids selectively ingested larger and positively charged plastics. MPs effectively reduced the uptake of NP and increased its gut passage time. Aggregation of positively and negatively charged MNPs also influenced the gut distribution and increased the gut passage time. The positively charged MPs accumulated in the middle and posterior gut, while aggregation of MNPs also increased acidification and esterase activity. These findings provided fundamental knowledge on the selectivity of MNPs and the microenvironmental responses of zooplankton guts.

Evolved tolerance to NaCl does not alter Daphnia response to acute heat stress

Evolved tolerance to NaCl does not alter Daphnia response to acute heat stress

Food level modifies the life-history response of Daphnia under chemically-induced predation stress

Food level modifies the life-history response of Daphnia under chemically-induced predation stress

Negative Effects of Cyanotoxins and Adaptative Responses of Daphnia.

The plethora of cyanobacterial toxins are an enormous threat to whole ecosystems and humans. Due to eutrophication and increases in lake temperatures from global warming, changes in the distribution of cyanobacterial toxins and selection of few highly toxic species/ strains are likely. Globally, one of the most important grazers that controls cyanobacterial blooms is Daphnia, a freshwater model organism in ecology and (eco)toxicology. Daphnia-cyanobacteria interactions have been studied extensively, often focusing on the interference of filamentous cyanobacteria with Daphnia's filtering apparatus, or on different nutritional constraints (the lack of essential amino acids or lipids) and grazer toxicity. For a long time, this toxicity only referred to microcystins. Currently, the focus shifts toward other deleterious cyanotoxins. Still, less than 10% of the total scientific output deals with cyanotoxins that are not microcystins; although these other cyanotoxins can occur just as frequently and at similar concentrations as microcystins in surface water. This review discusses the effects of different cyanobacterial toxins (hepatotoxins, digestive inhibitors, neurotoxins, and cytotoxins) on Daphnia and provides an elaborate and up-to-date overview of specific responses and adaptations of Daphnia. Furthermore, scenarios of what we can expect for the future of Daphnia-cyanobacteria interactions are described by comprising anthropogenic threats that might further increase toxin stress in Daphnia.

Behavioral Avoidance Response of Daphnia to Fungal Infection Caused by Metschnikowia Species in a Temperate Reservoir.

Simple SummaryThe negative effects of fungal infection on the survival and reproduction of cladocerans, a representative prey community in freshwater, are unexplored. In this study, we hypothesized that the winter migration pattern of Daphnia pulicaria, observed in the Anri Reservoir in South Korea, is the host’s defense response to fungal infection. Daphnia pulicaria was mainly distributed in the central bottom layer of the reservoir before winter (summer to autumn) but migrated to the littoral area during winter as fungal infections in the communities gradually spread in the bottom region. However, when the spread of infection was low, D. pulicaria did not migrate. The migrated individuals with dormant eggs were mostly infected and are believed to have migrated to the littoral area to freeze their dormant eggs. We found that dormant eggs of D. pulicaria obtained from ice crystals had lower hatching and infection rates than dormant eggs obtained adaptively in Daphnia mothers. Such a strategy is an efficient response of D. pulicaria to avoid the spread of fungal infection in communities and to maintain their continuous population growth.Morphological or behavioral defense mechanisms are important evolutionary strategies for the survival of prey. Studies have focused on predation and competition, but infection has been overlooked, despite being a determining factor of distribution and species diversity of prey. We hypothesized that the winter migration of Daphnia pulicaria is a community defense strategy to avoid fungal infection. To test this hypothesis, environmental variables and the Cladocera community, including D. pulicaria, were monitored in three study sections of the Anri Reservoir in the Republic of Korea during September 2010–August 2015. During three winter seasons, the density of infected D. pulicaria increased in all study sections, and they migrated from the central to the littoral area. Most of the infected individuals had dormant eggs in sexually reproducing mothers. However, when the proportion of non-infected individuals was higher than that of infected individuals, winter migration was not observed. Additional microcosm experiments showed that dormant eggs of D. pulicaria obtained from ice crystals in the littoral area had lower hatching and infection rates than those obtained from mothers moving from other zones. Therefore, the migration of D. pulicaria during winter is an active response to avoid intergenerational fungal infection.

Gene expression changes in Daphnia magna following waterborne exposure to cyanobacterial strains from the genus Nostoc

Cyanobacteria can produce highly potent cyanotoxins, however, limited information is provided about their toxicity mechanisms in exposed aquatic invertebrates at the molecular level. In the present study, the effects of cyanobacterial strains from the genus Nostoc (Nostoc Z1 and Nostoc 2S3B) in Daphnia magna after waterborne exposure were investigated. Examined endpoints included immobilization (survival) in acute toxicity tests and selected gene expression changes (cyp314, cyp360A8, gst, p-gp, vtg) analyzed by the quantitative real-time polymerase chain reaction (RT-PCR). In addition, enzyme-linked immunosorbent assay (ELISA) was performed to determine whether the observed changes could be due to the presence of microcystins, the most widespread group of cyanotoxins. The results of acute toxicity tests have shown only minor changes in survival rates, which have not exceeded 20% after 48 h of exposure to either strain. On the other hand, significant changes were recorded in molecular responses of Daphnia to tested strains. Treatment with the aquatic strain Nostoc Z1 altered the expression levels of all analyzed genes. Both strains caused a significant p-glycoprotein (p-gp) induction at 75 µg ml−1 which suggests the involvement of p-gp mediated multixenobiotic resistance mechanism (MXR) in facilitating excretion of toxic cyanobacterial compounds in daphnids. Additionally, these strains caused an increase in the expression levels of cyp360A8, indicating that genes related to detoxification processes could be sensitive indicators of cyanobacterial toxicity. Statistically significant induction of cyp314, as well as increases in expression of gst and vtg, were observed only after exposure to Nostoc Z1. This study indicates the potential of certain cyanobacterial metabolites to modify the expression of toxicant responsive genes involved in phase I and phase III of the xenobiotic metabolism, as well as possible interference with growth and reproduction in D. magna. Low microcystin concentrations found in both samples suggest that these cyanotoxins were not responsible for the detected toxic effects.

Morphological defences and defence–cost trade‐offs in Daphnia in response to two co‐occurring invertebrate predators

Abstract Inducible morphological defences are crucial for understanding predator–prey interactions. Such defences have been mostly studied in a single‐predator context, ignoring the fact that prey organisms are often exposed to multiple predators. In deep peri‐Alpine European lakes, the keystone grazer Daphnia coexists with two cladoceran predators, Bythotrephes longimanus and Leptodora kindtii. Up to now, life history and morphological responses of Daphnia to these two predators have not been analysed systematically. We studied the responses of two life history (age at first reproduction, and offspring production) and five morphological traits (body size, body width, head size, spina size, and eye diameter) of eight Daphnia galeata clones to the presence of Bythotrephes and Leptodora in a common garden experiment. We compared each response trait between treatments using linear mixed models, and investigated the covariation between defence traits and demographic costs (neonate production) for the two predators. Our results show that the responses of Daphnia are predator‐ and trait‐specific. Daphnia developed a typical helmet and a larger eye only in the presence of Bythotrephes, not in the presence of Leptodora. In contrast, both predators induced larger body sizes and longer spines. Age at first reproduction was latest and demographic costs were highest in the Bythotrephes treatment, suggesting that the development of a helmet exceeds the costs of spina elongation. The responses of Daphnia clones revealed a defence‐cost trade‐off for helmet formation in the Bythotrephes, and for spina elongation in the Leptodora treatment. Hence, despite Bythotrephes and Leptodora being closely related co‐occurring predators, Daphnia responds with a unique combination of trait changes and defence‐cost trade‐offs to the two predators. The presence of predator‐specific clonal defence‐cost trade‐offs suggests that the presence of these invertebrate predators can drive different evolutionary processes in natural zooplankton communities. Disentangling the evolutionary ecology of phenotypic responses of prey species to co‐occurring predators will require multi‐trait, multi‐clone studies of induced antipredator defences.

Calcium stress in Daphnia pulicaria and exposure to predator-derived cues: Making a bad situation worse?

Calcium concentrations ([Ca]) in some boreal lakes on the Canadian Shield have been declining over the previous couple of decades. With [Ca] in many lakes below 2 mg Ca/L, there are concerns about possible ecological effects of sustained Ca limitation on zooplankton assemblages. Here we examine whether short- and long-term effects of Ca stress on a keystone herbivore, Daphnia pulicaria, change with the presence of an invertebrate predator, Chaoborus flavicans. We did so by testing whether effects of low Ca on Daphnia pulicaria differ in the presence and absence of kairomones derived from C. flavicans. We compared mass-specific growth rates, body %Ca content, life-history traits, and survival of Daphnia exposed to a range of [Ca] with or without Chaoborus kairomones. We found a mix of individual and interactive effects of kairomones and low Ca supply on Daphnia responses. With longer and chronic exposure to both stressors, the effects of low Ca were intensified by the presence of kairomones, particularly for several reproductive measures (interbrood duration, mean brood size, and number of broods). Given the ubiquity of Chaoborus in softwater boreal lakes, our results show the need to consider their presence when assessing possible effects of low [Ca] on zooplankton assemblages.

Insights into the genetic basis of predator-induced response in Daphnia galeata.

Phenotypic plastic responses allow organisms to rapidly adjust when facing environmental challenges—these responses comprise morphological, behavioral but also life‐history changes. Alteration of life‐history traits when exposed to predation risk have been reported often in the ecological and genomic model organism Daphnia. However, the molecular basis of this response is not well understood, especially in the context of fish predation. Here, we characterized the transcriptional profiles of two Daphnia galeata clonal lines with opposed life histories when exposed to fish kairomones. First, we conducted a differential gene expression, identifying a total of 125 candidate transcripts involved in the predator‐induced response, uncovering substantial intraspecific variation. Second, we applied a gene coexpression network analysis to find clusters of tightly linked transcripts revealing the functional relations of transcripts underlying the predator‐induced response. Our results showed that transcripts involved in remodeling of the cuticle, growth, and digestion correlated with the response to environmental change in D. galeata. Furthermore, we used an orthology‐based approach to gain functional information for transcripts lacking gene ontology (GO) information, as well as insights into the evolutionary conservation of transcripts. We could show that our candidate transcripts have orthologs in other Daphnia species but almost none in other arthropods. The unique combination of methods allowed us to identify candidate transcripts, their putative functions, and evolutionary history associated with predator‐induced responses in Daphnia. Our study opens up to the question as to whether the same molecular signature is associated with fish kairomones‐mediated life‐history changes in other Daphnia species.

Interacting effects of simulated eutrophication, temperature increase, and microplastic exposure on Daphnia

The effects of multiple stressors are difficult to separate in field studies, and their interactions may be hard to predict if studied in isolation. We studied the effects of decreasing food quality (increase in cyanobacteria from 5 to 95% simulating eutrophication), temperature increase (by 3 °C), and microplastic exposure (1% of the diet) on survival, size, reproduction, and fatty acid composition of the model freshwater cladoceran Daphnia magna. We found that food quality was the major driver of Daphnia responses. When the amount of cyanobacteria increased from 5 to 95% of the diet, there was a drastic decrease in Daphnia survival (from 81 ± 15% to 24 ± 21%), juvenile size (from 1.8 ± 0.2 mm to 1.0 ± 0.1 mm), adult size (from 2.7 ± 0.1 mm to 1.1 ± 0.1 mm), and reproduction (from 13 ± 5 neonates per surviving adult to 0), but the decrease was not always linear. This was most likely due to lower availability of lipids, eicosapentaenoic acid (EPA), and sterols from the diet. Microplastic exposure did not affect Daphnia survival, size, or reproduction. Food quality had an interactive effect with temperature on fatty acid content of Daphnia. Total fatty acid content of Daphnia was almost 2-fold higher at 20 °C than at 23 °C when fed 50% cyanobacteria. This may have implications for higher trophic level consumers, such as fish, that depend on zooplankton for energy and essential lipids. Our findings suggest that as proportions of cyanobacteria increase, in tandem with water temperatures due to climate change, fish may encounter fewer and smaller Daphnia with lower lipid and EPA content.

Predators can influence the host-parasite dynamics of their prey via nonconsumptive effects.

Ecological communities are partly structured by indirect interactions, where one species can indirectly affect another by altering its interactions with a third species. In the absence of direct predation, nonconsumptive effects of predators on prey have important implications for subsequent community interactions. To better understand these interactions, we used a Daphnia‐parasite‐predator cue system to evaluate if predation risk affects Daphnia responses to a parasite. We investigated the effects of predator cues on two aspects of host–parasite interactions (susceptibility to infection and infection intensity), and whether or not these effects differed between sexes. Our results show that changes in response to predator cues caused an increase in the prevalence and intensity of parasite infections in female predator‐exposed Daphnia. Importantly, the magnitude of infection risk depended on how long Daphnia were exposed to the cues. Additionally, heavily infected Daphnia that were constantly exposed to cues produced relatively more offspring. While males were ~5× less likely to become infected compared to females, we were unable to detect effects of predator cues on male Daphnia–parasite interactions. In sum, predators, prey, and their parasites can form complex subnetworks in food webs, necessitating a nuanced understanding of how nonconsumptive effects may mediate these interactions.

Planktonic response to light as a pollution indicator

Ecological monitoring requires sensitive and effective approaches to detecting polluting substances. One such approach involves tracking the behavioral responses of plankton that is initially adapted to normal habitat conditions. Zooplankton such as Daphnia are filter feeders that are highly sensitive to pollution. We describe how a submersible holographic camera with additional attracting lighting (at a wavelength of 532 nm) can be used to track changes of Daphnia response to light for a number of pollutants, including potassium dichromate and crude oil. Our laboratory experiments showed that the sensitivity of this method of bioanalysis is comparable to standard laboratory methods, but has the additional advantage that it can be used in real time in lakes and other water areas, and hence is more versatile than standard methods.

Fear and food: Effects of predator‐derived chemical cues and stoichiometric food quality onDaphnia

AbstractWhile resource quality and predator‐derived chemical cues can each have profound effects on zooplankton populations and their function in ecosystems, the strength and direction of their interactive effects remain unclear. We conducted laboratory experiments to evaluate how stoichiometric food quality (i.e., algal carbon [C] : phosphorus [P] ratios) affects responses of the zooplankter,Daphnia pulicaria,to predator‐derived chemical cues. We compared growth rates, body P content, metabolic rates, life‐history shifts, and survival of differentially P‐nourishedDaphniain the presence and absence of chemical cues derived from fish predators. We found effects of predator cues and/or stoichiometric food quality on all measured traits ofDaphnia. Exposure to fish cues led to reduced growth and increased metabolic rates but had little effect on the body %P content ofDaphnia. Elevated algal C : P ratios reduced growth and body %P and increased mass‐specific respiration rates. While most of the effects of predator cues and algal C : P ratios ofDaphniawere non‐interactive, reduced survival and relatedly reduced population growth rates that resulted from P‐poor food were amplified in the presence of predator‐derived cues. Our results demonstrate that stoichiometric food quality interacts with antipredator responses ofDaphnia, but these effects are largely trait dependent and appear connected to animal life‐history evolution. Given the ubiquity of predators and P‐poor food in lake ecosystems, our results highlight the importance of the interactive responses of animals to predator cues and poor nutrition.

Rapid evolution of thermal plasticity in mountain lake Daphnia populations

Populations at risk of extinction due to climate change may be rescued by adaptive evolution or plasticity. Selective agents, such as introduced predators, may enhance or constrain plastic or adaptive responses to temperature. We tested responses of Daphnia to temperature by collecting populations from lakes across an elevational gradient in the presence and absence of fish predators (long‐term selection). We subsequently grew these populations at two elevations in field mesocosms over two years (short‐term selection), followed by a common‐garden experiment at two temperatures in the lab to measure life‐history traits. Both long‐term and short‐term selection affected traits, suggesting that genetic variation of plasticity within populations enabled individuals to rapidly evolve plasticity in response to high temperature. We found that short‐term selection by high temperature increased plasticity for growth rate in all populations. Fecundity was higher in populations from fishless lakes and body size showed greater plasticity in populations from warm lakes (long‐term selection). Neither body size nor fecundity were affected by short‐term thermal selection. These results demonstrate that plasticity is an important component of the life‐history response of Daphnia, and that genetic variation within populations enabled rapid evolution of plasticity in response to selection by temperature.