Light pollution due to human activities has become an emergent issue of environmental concern. Numerous human health and ecological detrimental effects of anthropogenicinduced changes to light conditions and especially of artificial light at night (ALAN) have been identified during recent years. Most studies have been conducted on terrestrial ecosystems and/or on vertebrates showing that ALAN can not only disrupt biological rhythms but also reduce biological fitness through changes in melatonin levels. Melatonin, a time-keeper hormone, plays a pivotal role of relaying information about changes in day-length and modulating circadian responses in physiology, metabolism and behavior. Evaluating the role of ALAN as an environmental endocrine disruptor with potential deleterious effects to biodiversity and ecosystems services is thus identified as a research priority. There is a need for mechanistic studies investigating links between ALAN and biological fitness. Moreover, we argue that these studies should include aquatic invertebrates and especially more realistic conditions. These are important research gaps within aquatic ecosystems that are particularly affected by ALAN since humans tend to settle near freshwater and coastal areas. Urbanization is steadily increasing worldwide imposing novel challenges on wild species living in urban/suburban areas. Besides light pollution, these ecosystems are usually also subjected to other anthropogenic stressors. Urban freshwaters are recipients of runoff from municipal and industrial discharges resulting in increased concentrations of chemical contaminants (including pesticides) with potential adverse consequences. Moreover, considerably warmer temperatures are observed in urbanized aquatic ecosystems (“urban heat islands”) due to urban air and ground temperatures, paved surfaces, and decreased riparian vegetation.
Given the ubiquity and co-occurrence of these stressors, it is critical to evaluate their combined impacts particularly in light of possible synergistic effects when multiple environmental stressors influence similar phenotypic traits and also due to their role as drivers of (micro)evolutionary responses. However, environmental risk assessment relies on standard ecotoxicity testing that does not consider changes in photoperiod, hence ignores ALAN.
Nevertheless, the mechanistic links dictating how shifting light conditions influence fitness and tolerance to additional stressors are currently not understood, and this limitation needs to be addressed. Melatonin may provide such a link. Besides its role in regulating circadian rhythms, it is involved in many other important functions in animals including antioxidant activity and detoxification, behavior, reproductive processes as well as immunity and metabolism regulation. Based on its widespread presence across taxa, its multi-functional role and the fact that chemical stressors can also affect circadian clocks, we hypothesize that plasticity in melatonin production can be a key physiological trait governing responses and potential adaptation not only to light pollution but also to chemical contamination and warming.
The SLEEP project will shed light on these issues by focusing on how ALAN can influence fitness and the impact of chemical contamination and warming in aquatic invertebrates. Through a combination of laboratory and mesocosm experiments where we
will manipulate both ALAN by using light emitting diodes and exogenous melatonin (to counter the ALANinduced reduction of internal melatonin), we will test:
i) to what degree ALAN affects melatonin levels and biological fitness in freshwater invertebrate species;
ii) how ALAN and the expected change in melatonin levels influence the toxicity of different pesticides and mediate responses to warming;
iii) the ecological consequences of ALAN for natural populations, species interactions and ecosystem functioning.
Relying on the strong expertise of the research team in ecotoxicology, ecophysiology, evolutionary ecology, freshwater ecology and urban ecology the results from this project will increase knowledge and awareness on light pollution and will be of indispensable value for an improved interpretation of the ecological effects of pesticides and warming in an urban context. From an evolutionary ecology perspective, doc menting the phenotypic plasticity and genetic variation of physiological processes mediated by melatonin, and of its consequences in terms of biological fitness will shed light on the mechanisms that can be under selection, driving biotic responses to climate change such as altered timing of seasonal events.
Finally, the outcomes of the SLEEP project are expected to provide scientific support for better urban environmental planning policies towards the protection and conservation of biodiversity and ecosystem services provided by urban freshwater ecosystems.
