Diverging responses to threats across generations in zooplankton

Neonicotinoid insecticide causes multigenerational impairment of inducible antipredator defenses in Daphnia

Nowadays organisms encounter not only natural challenges from predators but also significant anthropogenic stressors, such as insecticides, which can profoundly disrupt their normal growth and behavior. However, the knowledge on their potential interactions remains largely unknown, particularly regarding how insecticides may affect predator-prey interactions and prey responses across multiple generations. Here, we conducted a multigenerational experiment exposing two generations of Daphnia sinensis to predator kairomone from fish (Carassius auratus) and imidacloprid (a widely used neonicotinoid insecticide), both individually and in combination, followed by rearing two generations in a clean medium to examine effects on a series of traits including morphology, behavior, physiology, growth rate and reproduction. We found that fish kairomone and imidacloprid affected D. sinensis in different ways across generations, with effects remaining detectable even two generations after removing the threats. Combined stressors induced more pronounced adverse long-term effects than single stressors, affecting traits such as body size, thoracic limb movement, age at first reproduction and offspring number. Exposure to imidacloprid over generations led to a cumulative weakening of essential antipredator defenses, especially in the development of tail spine and reproductive traits, with more pronounced effects observed in the second exposure generation. Our findings highlight the complex interplay between natural and anthropogenic stressors and underscore the importance of considering multigenerational responses to fully understand their ecological impacts on aquatic ecosystems. Further research is essential to explore the underlying mechanisms driving these effects and to inform strategies for mitigating the ecological risks posed by continuous insecticide exposure.

The complex effects of modern oncogenic environments on the fitness, evolution and conservation of wildlife species

Growing evidence indicates that human activities are causing cancer rates to rise in both human and wildlife populations. This is due to the inability of ancestral anti-cancer defences to cope with modern environmental risks. The evolutionary mismatch between modern oncogenic risks and evolved cancer defences has far-reaching effects on various biological aspects at different timeframes, demanding a comprehensive study of the biology and evolutionary ecology of the affected species. Firstly, the increased activation of anti-cancer defences leads to excessive energy expenditure, affecting other biological functions and potentially causing health issues like autoimmune diseases. Secondly, tumorigenesis itself can impact important fitness-related parameters such as competitiveness, predator evasion, resistance to parasites, and dispersal capacity. Thirdly, rising cancer risks can influence the species' life-history traits, often favoring early reproduction to offset fitness costs associated with cancer. However, this strategy has its limits, and it may not ensure the sustainability of the species if cancer risks continue to rise. Lastly, some species may evolve additional anti-cancer defences, with uncertain consequences for their biology and future evolutionary path. In summary, we argue that the effects of increased exposure to cancer-causing substances on wildlife are complex, ranging from immediate responses to long-term evolutionary changes. Understanding these processes, especially in the context of conservation biology, is urgently needed.

The response of aquatic ecosystems to the interactive effects of stratospheric ozone depletion, UV radiation, and climate change

Variations in stratospheric ozone and changes in the aquatic environment by climate change and human activity are modifying the exposure of aquatic ecosystems to UV radiation. These shifts in exposure have consequences for the distributions of species, biogeochemical cycles, and services provided by aquatic ecosystems. This Quadrennial Assessment presents the latest knowledge on the multi-faceted interactions between the effects of UV irradiation and climate change, and other anthropogenic activities, and how these conditions are changing aquatic ecosystems. Climate change results in variations in the depth of mixing, the thickness of ice cover, the duration of ice-free conditions and inputs of dissolved organic matter, all of which can either increase or decrease exposure to UV radiation. Anthropogenic activities release oil, UV filters in sunscreens, and microplastics into the aquatic environment that are then modified by UV radiation, frequently amplifying adverse effects on aquatic organisms and their environments. The impacts of these changes in combination with factors such as warming and ocean acidification are considered for aquatic micro-organisms, macroalgae, plants, and animals (floating, swimming, and attached). Minimising the disruptive consequences of these effects on critical services provided by the world's rivers, lakes and oceans (freshwater supply, recreation, transport, and food security) will not only require continued adherence to the Montreal Protocol but also a wider inclusion of solar UV radiation and its effects in studies and/or models of aquatic ecosystems under conditions of the future global climate.

Ancestral environment determines the current reaction to ultraviolet radiation in Daphnia magna

An individual's phenotype can be altered by direct contact with its present environment but also by environmental features experienced by previous generations, that is, parental or grandparental effects. However, the strength and direction of these transgenerational effects may be highly variable according to the ecological conditions experienced by ancestral generations. Here, we performed a reciprocal split-brood experiment to compare transgenerational responses to the threat of ultraviolet radiation (UVR) in the zooplankter Daphnia magna, which had, or had not, been exposed to UVR for more than 150 generations. We found that the environment at which parents and grandparents were reared significantly influenced both behavior and life-history traits of their descendants. However, such transgenerational responses differed between D. magna individuals with contrasting ancestral stress history, that is, when exposed to UVR previously unexposed individuals rapidly changed their behavior and life-history traits, whereas individuals previously exposed to UVR showed less pronounced response when the UVR threat level relaxed. Hence, we here demonstrate an asymmetric transgenerational plasticity in response to UVR threat. The findings advance our understanding on the evolutionary ecology of such transgenerational effects and their potential role in response to changes in the local environment.

Environmentally induced DNA methylation is inherited across generations in an aquatic keystone species

Transgenerational inheritance of environmentally induced epigenetic marks can have significant impacts on eco-evolutionary dynamics, but the phenomenon remains controversial in ecological model systems. We used whole-genome bisulfite sequencing of individual water fleas (Daphnia magna) to assess whether environmentally induced DNA methylation is transgenerationally inherited. Genetically identical females were exposed to one of three natural stressors, or a de-methylating drug, and their offspring were propagated clonally for four generations under control conditions. We identified between 70 and 225 differentially methylated CpG positions (DMPs) in F1 individuals whose mothers were exposed to a natural stressor. Roughly half of these environmentally induced DMPs persisted until generation F4. In contrast, treatment with the drug demonstrated that pervasive hypomethylation upon exposure is reset almost completely after one generation. These results suggest that environmentally induced DNA methylation is non-random and stably inherited across generations in Daphnia, making epigenetic inheritance a putative factor in the eco-evolutionary dynamics of freshwater communities.

Population connectivity, dispersal, and swimming behavior in Daphnia

The water flea Daphnia has the capacity to respond rapidly to environmental stressors, to disperse over large geographical scales, and to preserve its genetic material by forming egg banks in the sediment. Spatial and temporal distributions of D. magna have been extensively studied over the last decades using behavioral or genetic tools, although the correlation between the two has rarely been the focus. In the present study, we therefore investigated the population genetic structure and behavioral response to a lethal threat, ultraviolet radiation (UVR), among individuals from two different water bodies. Our results show two genetic populations with moderate gene flow, highly correlated with geographical location and with inheritable traits through generations. However, despite the strong genetic differences between populations, we show homogeneous refuge demand between populations when exposed to the lethal threat solar UVR.

Diverging responses to threats across generations in zooplankton

Our understanding on how organisms evolutionarily cope with simultaneously occurring, multiple threats over generations is still elusive. In a long‐term experimental study, we therefore exposed clones of a freshwater cladoceran, Daphnia magna, to threats from predation and ultraviolet radiation (UVR) during three consecutive parthenogenetic generations. We show that Daphnia can adapt to different sets of threats within three generations through modifying morphology, swimming behavior, or life‐history traits. When faced with predator cues, D. magna responded with reduced body size, whereas exposure to UVR induced behavioral tolerance when again exposed to this threat. Such UVR‐tolerant behavior was initially associated with a reduced clutch size, but Daphnia restored the reproductive output gradually through generations. The findings advance our understanding on how those common invertebrates, with a global distribution, are able to persist and rapidly become successful in a changing environment.