Exposure to Artificial Light at Night and the Consequences for Flora, Fauna, and Ecosystems

Light pollution regulations and where to find them

The growing concerns about the adverse impacts of light pollution on astronomy, the environment, biodiversity, human health, and energy use have brought increased attention to the issue on legal and political agendas. Various international frameworks and governments at different levels have taken action to mitigate the impacts of nighttime lighting. This article provides an overview of regulatory instruments adopted to protect the nocturnal environment, explaining triggers for regulatory changes, using an interdisciplinary perspective. It proposes a classification of these instruments based on their nature: (1) law or policy, (2) binding or non-binding, and by their (3) levels and (4) areas of implementation, supported by specific examples. The article identifies current shortcomings and recommends future regulatory changes to address light pollution effectively. This interdisciplinary research aims to provide a better understanding of light pollution as an environmental concern and explains the development of light pollution regulations, helping to foster interdisciplinary communication and the adoption of more adequate regulatory measures to address light pollution. Additionally, this study intends to fill the gap in legal and policy research related to light pollution.

The association between outdoor artificial light at night exposure and antenatal depression and anxiety symptoms: A retrospective cohort study in China

BACKGROUND

Outdoor artificial light at night (ALAN) has emerged as a significant source of environmental pollution, however its association with antenatal depression and anxiety symptoms has been rarely explored before.

METHODS

This study was based on a cohort study conducted at the Maternal and Child Health Care Center in Ma'anshan City, Anhui Province, China, which ultimately included 1047 pregnant women. Depression and anxiety symptoms were evaluated utilizing the self-administered Patient Health Questionnaire (PHQ-9) and the 7-item Generalized Anxiety Scale (GAD-7), respectively. Exposure levels to outdoor ALAN were calculated utilizing satellite data and the participants' usual addresses. Logistic regression and restricted cubic spline were used to assess the association between exposure to outdoor ALAN and depression and anxiety symptoms in pregnant women.

RESULTS

After adjusting for confounding factors, high ALAN exposure during the pre-pregnancy period (ORdepression = 3.16, 95% CI: 1.14-8.75; ORanxiety = 3.09, 95% CI: 1.51-6.28) and first trimester (ORdepression = 2.90, 95% CI: 1.13-7.45; ORanxiety = 3.11, 95% CI: 1.55-6.25) were associated with increased risks of antenatal depression and anxiety symptoms. Restricted cubic spline analyses showed the above associations were not nonlinear.

CONCLUSION

Our study is the first to propose that exposure to high levels of outdoor ALAN three months before pregnancy and during the first trimester of pregnancy is a risk factor for antenatal depression and anxiety symptoms.

Artificial Light Increases Nighttime Prevalence of Predatory Fishes, Altering Community Composition on Coral Reefs

Artificial light at night (ALAN) is an anthropogenic pollutant that is intensifying and expanding in marine environments, but experimental studies of community-level effects are generally lacking. The inshore, shallow, and clear-water locations of coral reefs and their diverse photosensitive inhabitants make these ecosystems highly susceptible to biological disturbances; at the same time, their biodiversity and accessibility make them model systems for wider insight. Here, we experimentally manipulated ALAN using underwater LED lights on a Polynesian reef system to investigate the influence on localised nighttime fish communities compared to control sites without ALAN. We collected infrared video censuses of baseline communities prior to manipulation, which we repeated following short-term (mean of three nights) and prolonged (mean of 25 nights) exposures to ALAN. Short-term ALAN exposure did not induce any significant alterations to the nighttime fish community, but prolonged ALAN exposure increased nighttime species richness. Species compositions exposed to prolonged ALAN were more dissimilar from their baseline compared to control sites. The difference between community compositions at prolonged ALAN exposure and control sites was not apparent at the family level; instead, it was observed from the composition of trait guilds. Following prolonged ALAN exposure, more diurnal and nocturnal predatory species (piscivores, invertivores, and planktivores)-particularly those that are site-attached or mobile within reefs-were present in nighttime assemblages. Our experimental findings show that coastal ALAN could cause trophic imbalances and circadian disturbances in localised nighttime reef fish communities. Given that community-wide consequences were only apparent after prolonged ALAN exposure suggests that management of the duration of artificial lighting could potentially be used to reduce impacts on marine ecosystems.

Behavioural and transgenerational effects of artificial light at night (ALAN) of varying spectral compositions in zebrafish (Danio rerio)

Artificial light at night (ALAN) can disrupt the natural behaviour, physiology, and circadian rhythms of organisms exposed to it, and therefore presents a significant and widespread ecological concern. ALAN typically comprises a wide range of wavelengths, and different wavelengths have different effects on circadian clocks. In the animals investigated thus far, short and middle wavelengths are intensely involved in synchronisation and entrainment, but we still have a poor understanding of how different wavelengths might affect behaviour when animals are exposed to ALAN, in particular whether some wavelengths are disproportionally detrimental. This experiment examined the direct and transgenerational effects of 10 different wavelength treatments of ALAN on behaviour in zebrafish (Danio rerio), a diurnally active model organism. Across a 10-day period, female zebrafish were exposed to either a monochromatic wavelength, white light ALAN, or to a control treatment, and the individual impacts of each treatment on locomotion and anxiety-like behaviours were examined both for solitary fish and fish in groups. We found the strongest impact at short wavelengths (365 to 470 nm), with individuals and groups of zebrafish showing more anxiety-like behaviour after fewer nights of ALAN exposure relative to the other wavelengths. Furthermore, F1 offspring born from ALAN-exposed mothers displayed less frequent movement and shorter movement distances despite never being exposed to ALAN themselves, regardless of the spectral treatment. Our results highlight both the specific and broad-spectrum potential for ALAN to cause disruption to locomotion in adult zebrafish and their offspring.

Light pollution disrupts seasonal reproductive phenotypes and reduces lifespan in the West Nile vector, Culex pipiens

Females of the Northern House mosquito, Culex pipiens, are important disease vectors as they transmit pathogens including West Nile virus. These females survive the winter by entering diapause, a state of dormancy, characterized by the accumulation of lipids, cessation of blood-feeding, and reproductive arrest. Diapause is cued by photoperiod, so as days become short in late summer and early fall, female Cx. pipiens prepare to overwinter and disease transmission decreases. We previously demonstrated that Artificial light at night (ALAN) causes female Cx. pipiens to avert diapause and continue to blood-feed when reared under short-day conditions. Additionally, light pollution alters seasonal differences in mosquito activity and nutrient reserves. However, it is unclear how exposure to ALAN affects blood-feeding and fecundity in long-day reared females, as well as the survival of Cx. pipiens exposed under both short and long-day conditions. In this study, we hypothesized that females exposed to ALAN in long-day conditions would have a lower proclivity to blood-feed, reduced fecundity, and reduced survival. Results from our lab-based experiments demonstrate that females exposed to ALAN in long-day conditions were less likely to blood-feed but were more fecund than long-day reared females that were not exposed to ALAN, and that ALAN exposure did not affect lifespan of long-day reared females. Additionally, we hypothesized ALAN exposure under short-day conditions would reduce survival, and our data supports this hypothesis. Overall, our results demonstrate that ALAN is an important urban stressor that has the potential to affect reproduction and lifespan in mosquitoes, and therefore has the potential to create evolutionary tradeoffs.

Exposure to constant artificial light alters honey bee sleep rhythms and disrupts sleep

Artificial light at night (ALAN) changes animal behavior in multiple invertebrates and vertebrates and can result in decreased fitness. However, ALAN effects have not been studied in European honey bees (Apis mellifera), an important pollinator in which foragers show strong circadian rhythmicity. Colonies can be exposed to ALAN in swarm clusters, when bees cluster outside the nest on hot days and evenings, and, in limited cases, when they build nests in the open. We captured and maintained foragers in incubated cages and subjected them to constant light (LL), constant dark (DD), or 12 h light:12 h dark (LD) cycle, and observed them with infrared cameras. After 79 h, there was a significant interaction of treatment and time because LL bees slept less. In detail, the bees maintained a regular sleep pattern for three days but LL bees showed a shift on the fourth day. LL bees had the largest sleep differences from LD controls, with trends of lengthened periods and increased phase misalignment from both LD and DD bees. LL bees also experienced significantly more disturbances from their nestmates and preferred to sleep in the lower portion of the cages, which had significantly lower light intensity. These findings suggest that ALAN can disrupt the sleep of honey bee foragers, which has implications for their behavior and overall colony health.

Is there direct photoentrainment in the goldfish liver? Wavelength-dependent regulation of clock genes and investigation of the opsin 7 family

Widespread direct photoentrainment in zebrafish peripheral tissues is linked to diverse non-visual opsins. To explore whether this broadly distributed photosensitivity is specific to zebrafish or is a general teleost feature, we investigated hepatic photosynchronization in goldfish. First, we focused on the opsin 7 family (OPN7, a key peripheral novel opsin in zebrafish), investigating its presence in the goldfish liver. Subsequently, we studied whether light can directly entrain the goldfish liver and retina clocks. Silico analysis revealed seven OPN7 paralogs from four gene families, suggesting expansion through whole-genome and tandem duplications. The paralogs of families OPN7a, OPN7b, and OPN7d were mainly localized in neural tissues, while OPN7c paralogs were more abundant in peripheral tissues-including the liver-suggesting divergent roles. Light (independently of the wavelength employed) directly induced the per2a clock gene in the retina both in vivo and in vitro, confirming expected photoentrainment. However, in the liver, photoinduction of per1a and cry1a only occurred in vivo, not in vitro. These results suggest an indirect light-entrainment mechanism of the goldfish hepatic clock, possibly mediated by other oscillators or photosensitive organs. Our findings challenge the assumption of widespread direct photosensitivity in the peripheral tissues of teleosts. Further research is needed to understand the role of tissue-specific photoentrainment and non-visual opsins in diverse teleost species.

Urban house finches are more resistant to the effects of artificial light at night

Rapid urbanization of habitats alters the physical, chemical, auditory, and photic environments of human and wild animal inhabitants. One of the most widespread transformations is caused by artificial light at night (ALAN), but it is not clear the extent to which individuals acclimate to such rapid environmental change. Here, we tested the hypothesis that urban birds show increased resistance to harmful behavioral, parasitological, and physiological effects of ALAN. We captured house finches (Haemorhous mexicanus), a bird that commonly inhabits cities and their natural surroundings, from two urban and two rural sites in Phoenix, Arizona, USA, which differ by both degree of urbanization and by multiple orders of magnitude in ALAN intensity, and placed them in a common garden laboratory setting. We exposed half of the birds from each habitat type to ecologically relevant levels of night lighting during the subjective night and found that, while ALAN exposure reduced sleep in both urban and rural birds, ALAN-exposed urban birds were able to sleep longer than ALAN-exposed rural birds. We also found that ALAN exposure increased the proliferation rate of an intestinal coccidian parasite (Isospora spp.) in both urban and rural birds, but that the rate of proliferation was lower in urban relative to rural birds. We found that night lighting suppressed titers of feather corticosterone in rural but not urban birds, suggesting that light impairs HPA function through chronic stress or suppression of its circadian rhythmicity, and that urban birds were again resistant to this effect. Mediation analyses show that the effect of ALAN exposure in rural birds was significantly sleep-mediated for feather corticosterone but not coccidiosis, suggesting a diversity of mechanisms by which ALAN alters physiology. We contribute further evidence that animals from night-lit habitats can develop resistance to ALAN and its detrimental effects.

Functional diversification process of opsin genes for teleost visual and pineal photoreceptions

Most vertebrates have a rhodopsin gene with a five-exon structure for visual photoreception. By contrast, teleost fishes have an intron-less rhodopsin gene for visual photoreception and an intron-containing rhodopsin (exo-rhodopsin) gene for pineal photoreception. Here, our analysis of non-teleost and teleost fishes in various lineages of the Actinopterygii reveals that retroduplication after branching of the Polypteriformes produced the intron-less rhodopsin gene for visual photoreception, which converted the parental intron-containing rhodopsin gene into a pineal opsin in the common ancestor of the Teleostei. Additional analysis of a pineal opsin, pinopsin, shows that the pinopsin gene functions as a green-sensitive opsin together with the intron-containing rhodopsin gene for pineal photoreception in tarpon as an evolutionary intermediate state but is missing in other teleost fishes, probably because of the redundancy with the intron-containing rhodopsin gene. We propose an evolutionary scenario where unique retroduplication caused a "domino effect" on the functional diversification of teleost visual and pineal opsin genes.

Gyrodactylus in the spotlight: how exposure to light impacts disease and the feeding behavior of the freshwater tropical guppy (Poecilia reticulata)

Artificial light at night (ALAN) negatively impacts organisms in many ways, from their feeding behaviors to their response and ability to deal with disease. Our knowledge of ALAN is focused on hosts, but we must also consider their parasites, which constitute half of all described animal species. Here, we assessed the impact of light exposure on a model host-parasite system (Poecilia reticulata and the ectoparasitic monogenean Gyrodactylus turnbulli). First, parasite-free fish were exposed to 12:12 h light:dark (control) or 24:0 h light:dark (ALAN) for 21 days followed by experimental infection. Second, naturally acquired G. turnbulli infections were monitored for 28 days during exposure of their hosts to a specified light regime (6:18 h, 12:12 h, or 24:0 h light:dark). Experimentally infected fish exposed to constant light had, on average, a greater maximum parasite burden than controls, but no other measured parasite metrics were impacted. Host feeding behavior was also significantly affected: fish under ALAN fed faster and took more bites than controls, whilst fish exposed to reduced light fed slower. Thus, ALAN can impact parasite burdens, even in the short term, and altering light conditions will impact fish feeding behavior. Such responses could initiate disease outbreaks or perturb food-webs with wider ecological impacts.

Environmental pollutants and exosomes: A new paradigm in environmental health and disease

This study investigates the intricate interplay between environmental pollutants and exosomes, shedding light on a novel paradigm in environmental health and disease. Cellular stress, induced by environmental toxicants or disease, significantly impacts the production and composition of exosomes, crucial mediators of intercellular communication. The heat shock response (HSR) and unfolded protein response (UPR) pathways, activated during cellular stress, profoundly influence exosome generation, cargo sorting, and function, shaping intercellular communication and stress responses. Environmental pollutants, particularly lipophilic ones, directly interact with exosome lipid bilayers, potentially affecting membrane stability, release, and cellular uptake. The study reveals that exposure to environmental contaminants induces significant changes in exosomal proteins, miRNAs, and lipids, impacting cellular function and health. Understanding the impact of environmental pollutants on exosomal cargo holds promise for biomarkers of exposure, enabling non-invasive sample collection and real-time insights into ongoing cellular responses. This research explores the potential of exosomal biomarkers for early detection of health effects, assessing treatment efficacy, and population-wide screening. Overcoming challenges requires advanced isolation techniques, standardized protocols, and machine learning for data analysis. Integration with omics technologies enhances comprehensive molecular analysis, offering a holistic understanding of the complex regulatory network influenced by environmental pollutants. The study underscores the capability of exosomes in circulation as promising biomarkers for assessing environmental exposure and systemic health effects, contributing to advancements in environmental health research and disease prevention.

Phosphate phosphors with anti-thermal quenching properties for urban ecological lighting

White light-emitting diode (LED) for night lighting disrupts photoperiod in plants, which affects the plant's photosynthesis. Therefore, it is necessary to find a new type of white LED with little effect on plant photosynthesis. In this study, a series of phosphate phosphors Ca9NaY2/3(PO4)7:Dy3+ (CNYP:Dy3+) were synthesized. Cation Li+ substitute Na+ were used to improve the luminescence properties of CNYP:Dy3+ phosphor. The CNYP:Dy3+ phosphor exhibits visible white light emission with emission peaks at 480 nm (blue light) and 570 nm (yellow light) excited by the near ultraviolet light 350 nm. The optimal concentration of Dy3+ was 0.10 mol, and the mechanism of concentration quenching was evaluated as energy migration among the nearest or next-nearest Dy3+. The substitution of Na+ by Li+ of CNYP:0.10Dy3+ improves the internal quantum efficiency from 30.24 % to 59.05 %, and presents good near-zero thermal quenching performance at 423 K. To assess the suitability of this phosphor for urban ecological lighting, the spectrum resemblance (SR) index between the electroluminescence spectrum of the prepared pc-LED and the absorption spectra of chlorophyll a and b was evaluated as 6.63 % and 18.61 %, respectively. This work exhibits a feasible scheme for the development of urban ecological lighting.

Endocrine-circadian interactions in birds: implications when nights are no longer dark

Biological clocks are evolved time-keeping systems by which organisms rhythmically coordinate physiology within the body, and align it with rhythms in their environment. Clocks are highly sensitive to light and are at the interface of several major endocrine pathways. Worryingly, exposure to artificial-light-at-night (ALAN) is rapidly increasing in ever more extensive parts of the world, with likely impact on wild organisms mediated by endocrine-circadian pathways. In this overview, we first give a broad-brush introduction to biological rhythms. Then, we outline interactions between the avian clock, endocrine pathways, and environmental and internal modifiers. The main focus of this review is on the circadian hormone, melatonin. We summarize information from avian field and laboratory studies on melatonin and its relationships with behaviour and physiology, including often neglected developmental aspects. When exposed to ALAN, birds are highly vulnerable to disruption of behavioural rhythms and of physiological systems under rhythmic control. Several studies suggest that melatonin is likely a key mediator for a broad range of effects. We encourage further observational and experimental studies of ALAN impact on melatonin, across the full functional range of this versatile signalling molecule, as well as on other candidate compounds at the endocrine-circadian interface. This article is part of the theme issue 'Endocrine responses to environmental variation: conceptual approaches and recent developments'.

Endocrine responses to environmental variation

Hormones regulate most physiological functions and life history from embryonic development to reproduction. In addition to their roles in growth and development, hormones also mediate responses to the abiotic, social and nutritional environments. Hormone signalling is responsive to environmental changes to adjust phenotypes to prevailing conditions. Both hormone levels and receptor densities can change to provide a flexible system of regulation. Endocrine flexibility connects the environment to organismal function, and it is central to understanding environmental impacts and their effect on individuals and populations. Hormones may also act as a 'sensor' to link environmental signals to epigenetic processes and thereby effect phenotypic plasticity within and across generations. Many environmental parameters are now changing in unprecedented ways as a result of human activity. The knowledge base of organism-environmental interactions was established in environments that differ in many ways from current conditions as a result of ongoing human impacts. It is an urgent contemporary challenge to understand how evolved endocrine responses will modulate phenotypes in response to anthropogenic environmental impacts including climate change, light-at-night and chemical pollution. Endocrine responses play a central role in ecology, and their integration into conservation can lead to more effective outcomes. This article is part of the theme issue 'Endocrine responses to environmental variation: conceptual approaches and recent developments'.

Thyroid hormone links environmental signals to DNA methylation

Environmental conditions experienced within and across generations can impact individual phenotypes via so-called 'epigenetic' processes. Here we suggest that endocrine signalling acts as a 'sensor' linking environmental inputs to epigenetic modifications. We focus on thyroid hormone signalling and DNA methylation, but other mechanisms are likely to act in a similar manner. DNA methylation is one of the most important epigenetic mechanisms, which alters gene expression patterns by methylating cytosine bases via DNA methyltransferase enzymes. Thyroid hormone is mechanistically linked to DNA methylation, at least partly by regulating the activity of DNA methyltransferase 3a, which is the principal enzyme that mediates epigenetic responses to environmental change. Thyroid signalling is sensitive to natural and anthropogenic environmental impacts (e.g. light, temperature, endocrine-disrupting pollution), and here we propose that thyroid hormone acts as an environmental sensor to mediate epigenetic modifications. The nexus between thyroid hormone signalling and DNA methylation can integrate multiple environmental signals to modify phenotypes, and coordinate phenotypic plasticity at different time scales, such as within and across generations. These dynamics can have wide-ranging effects on health and fitness of animals, because they influence the time course of phenotypic adjustments and potentially the range of environmental stimuli that can elicit epigenetic responses. This article is part of the theme issue 'Endocrine responses to environmental variation: conceptual approaches and recent developments'.

Coping with light pollution in urban environments: Patterns and challenges

Artificial light at night is a growing environmental problem that is especially pronounced in urban environments. Yet, impacts on urban wildlife have received scant attention and patterns and consequences are largely unknown. Here, I present a conceptual framework outlining the challenges species encounter when exposed to urban light pollution and how they may respond through plastic adjustments and genetic adaptation. Light pollution interferes with biological rhythms, influences behaviors, fragments habitats, and alters predation risk and resource abundance, which changes the diversity and spatiotemporal distribution of species and, hence, the structure and function of urban ecosystems. Furthermore, light pollution interacts with other urban disturbances, which can exacerbate negative effects on species. Given the rapid growth of urban areas and light pollution and the importance of healthy urban ecosystems for human wellbeing, more research is needed on the impacts of light pollution on species and the consequences for urban ecosystems.

Metal accumulation and genetic adaptation of Oryza sativa to Cadmiun and Chromium heavy metal stress: A hydroponic and RAPD analyses

This research was performed to assess the influence of Cd and Cr metals on growth, pigments, antioxidant, and genomic stability of Oryza sativa indica and Oryza sativa japonica were investigated under hydroponic conditions. The results revealed that significant metal influence on test crop growth, pigment content, metal stress balancing antioxidant activity in a dose dependent manner. Since, while at elevated (500 ppm) concentration of Cd as well as Cr metals the pigment (total chlorophyll, chlorophyll a, b and carotenoids) level was reduced than control; however antioxidant activity (total antioxidant, H2O2, and NO) was considerably improved as protective mechanisms to combat the metal toxicity and support the plant growth. Furthermore, the test crops under typical hydroponic medium (loaded with Cd and Cr as 200, 300, 400, and 500 ppm) growth conditions, effectively absorb the metals from medium and accumulated in the root and least quantity was translocated to the shoot of this test crops. Furthermore, typical RAPD analysis with 10 universal primers demonstrated that the genomic DNA of the test crops was adaptable to develop metal resistance and ensure crop growth under increased concentrations (500 ppm) of tested heavy metals. These findings suggest that these edible crops have the ability to accumulate Cd along with Cr metals, and additionally that their genetic systems have the ability to adapt to metal-stressed environments.

The blue light hazard and its use on the evaluation of photochemical risk for domestic lighting. An in vivo study

BACKGROUND

Nowadays artificial light highly increases human exposure to light leading to circadian rhythm and sleep perturbations. Moreover, excessive exposure of ocular structures to photons can induce irreversible retinal damage. Meta-analyses showed that sunlight exposure influences the age of onset and the progression of Age-related macular degeneration (AMD), the leading cause of blindness in people over fifty-year old. Currently, the blue-light hazard (BLH) curve is used in the evaluation of the phototoxicity of a light source for domestic lighting regulations.

OBJECTIVES

Here, we analyze the phototoxicity threshold in rats and investigate the role played by the light spectrum, assessing the relevance of the use of the BLH-weighting to define phototoxicity.

METHODS

We exposed albino rats to increasing doses of blue and white light, or to lights of different colors to evaluate the impact of each component of the white light spectrum on phototoxicity. Cellular mechanisms of cell death and cellular stress induced by light were analyzed.

RESULTS

Our results show that the phototoxicity threshold currently accepted for rats is overestimated by a factor of 50 when considering blue light and by a factor of 550 concerning white light. This is the result of the toxicity induced by green light that increases white light toxicity by promoting an inflammatory response. The content of green in white light induces 8 fold more invasion of macrophages in the retina than the content of blue light. Moreover, the use of BLH-weighting does not evaluate the amount of red radiations contained in white light that mitigates damage by inhibiting the nuclear translocation of L-DNase II and reducing by 33% the number of TUNEL-positive cells.

DISCUSSION

These findings question the current methods to determine the phototoxicity of a light source and show the necessity to take into account the entire emission spectrum. As current human phototoxicity thresholds were estimated with the same methods used for rats, our results suggest that they might need to be reconsidered.

A framework for untangling the consequences of artificial light at night on species interactions

Although much evidence exists showing organismal consequences from artificial light at night (ALAN), large knowledge gaps remain regarding ALAN affecting species interactions. Species interactions occur via shared spatio-temporal niches among species, which may be determined by natural light levels. We review how ALAN is altering these spatio-temporal niches through expanding twilight or full Moon conditions and constricting nocturnal conditions as well as creating patches of bright and dark. We review literature from a database to determine if ALAN is affecting species interactions via spatio-temporal dynamics. The literature indicates a growing interest in ALAN and species interactions: 58% of the studies we analysed have been published since 2020. Seventy-five of 79 studies found ALAN altered species interactions. Enhancements and reductions of species interactions were equally documented. Many studies revealed ALAN affecting species interactions spatially, but few revealed temporal alterations. There are biases regarding species interactions and ALAN-most studies investigated predator-prey interactions with vertebrates as predators and invertebrates as prey. Following this literature review, we suggest avenues, such as remote sensing and animal tracking, that can guide future research on the consequences of ALAN on species interactions across spatial and temporal axes. This article is part of the theme issue 'Light pollution in complex ecological systems'.

Light pollution in complex ecological systems

Light pollution has emerged as a burgeoning area of scientific interest, receiving increasing attention in recent years. The resulting body of literature has revealed a diverse array of species-specific and context-dependent responses to artificial light at night (ALAN). Because predicting and generalizing community-level effects is difficult, our current comprehension of the ecological impacts of light pollution on complex ecological systems remains notably limited. It is critical to better understand ALAN's effects at higher levels of ecological organization in order to comprehend and mitigate the repercussions of ALAN on ecosystem functioning and stability amidst ongoing global change. This theme issue seeks to explore the effects of light pollution on complex ecological systems, by bridging various realms and scaling up from individual processes and functions to communities and networks. Through this integrated approach, this collection aims to shed light on the intricate interplay between light pollution, ecological dynamics and humans in a world increasingly impacted by anthropogenic lighting. This article is part of the theme issue 'Light pollution in complex ecological systems'.

Part-night exposure to artificial light at night has more detrimental effects on aphid colonies than fully lit nights

Artificial light at night (ALAN) threatens natural ecosystems globally. While ALAN research is increasing, little is known about how ALAN affects plants and interactions with other organisms. We explored the effects of ALAN on plant defence and plant-insect interactions using barley (Hordeum vulgare) and the English grain aphid (Sitobion avenae). Plants were exposed to 'full' or 'part' nights of 15-20 lux ALAN, or no ALAN 'control' nights, to test the effects of ALAN on plant growth and defence. Although plant growth was only minimally affected by ALAN, aphid colony growth and aphid maturation were reduced significantly by ALAN treatments. Importantly, we found strong differences between full-night and part-night ALAN treatments. Contrary to our expectations, part ALAN had stronger negative effects on aphid colony growth than full ALAN. Defence-associated gene expression was affected in some cases by ALAN, but also positively correlated with aphid colony size, suggesting that the effects of ALAN on plant defences are indirect, and regulated via direct disruption of aphid colonies rather than via ALAN-induced upregulation of defences. Mitigating ecological side effects of ALAN is a complex problem, as reducing exposure to ALAN increased its negative impact on insect herbivores. This article is part of the theme issue 'Light pollution in complex ecological systems'.

Light pollution of freshwater ecosystems: principles, ecological impacts and remedies

Light pollution caused by artificial light at night (ALAN) is increasingly recognized as a major driver of global environmental change. Since emissions are rapidly growing in an urbanizing world and half of the human population lives close to a freshwater shoreline, rivers and lakes are ever more exposed to light pollution worldwide. However, although light conditions are critical to aquatic species, and freshwaters are biodiversity hotspots and vital to human well-being, only a small fraction of studies conducted on ALAN focus on these ecosystems. The effects of light pollution on freshwaters are broad and concern all levels of biodiversity. Experiments have demonstrated diverse behavioural and physiological responses of species, even at low light levels. Prominent examples are skyglow effects on diel vertical migration of zooplankton and the suppression of melatonin production in fish. However, responses vary widely among taxa, suggesting consequences for species distribution patterns, potential to create novel communities across ecosystem boundaries, and cascading effects on ecosystem functioning. Understanding, predicting and alleviating the ecological impacts of light pollution on freshwaters requires a solid consideration of the physical properties of light propagating in water and a multitude of biological responses. This knowledge is urgently needed to develop innovative lighting concepts, mitigation strategies and specifically targeted measures. This article is part of the theme issue 'Light pollution in complex ecological systems'.

Light pollution may alter host-parasite interactions in aquatic ecosystems

With growing human populations living along freshwater shores and marine coastlines, aquatic ecosystems are experiencing rising levels of light pollution. Through its effects on hosts and parasites, anthropogenic light at night can disrupt host-parasite interactions evolved under a normal photoperiod. Yet its impact on aquatic parasites has been ignored to date. Here, I discuss the direct effects of light on the physiology and behaviour of parasite infective stages and their hosts. I argue that night-time lights can change the spatiotemporal dynamics of infection risk and drive the rapid evolution of parasites. I then highlight knowledge gaps and how impacts on parasitic diseases should be incorporated into the design of measures aimed at mitigating the impact of anthropogenic light on wildlife.

The effects of artificial light at night on behavioral rhythm and related gene expression are wavelength dependent in the oyster Crassostrea gigas

Artificial light at night (ALAN) constitutes a growing threat to coastal ecosystems by altering natural light cycles, which could impair organisms' biological rhythms, with resulting physiological and ecological consequences. Coastal ecosystems are strongly exposed to ALAN, but its effects on coastal organisms are poorly studied. Besides ALAN's intensity, ALAN's quality exposure may change the impacts on organisms. This study aims to characterize the effects of different ALAN's spectral compositions (monochromatic wavelength lights in red (peak at 626 nm), green (peak at 515 nm), blue (peak at 467 nm), and white (410-680 nm) light) at low and realistic intensity (1 lx) on the oyster Crassostrea gigas daily rhythm. Results reveal that all ALAN's treatments affect the oysters' daily valve activity rhythm in different manners and the overall expression of the 13 studied genes. Eight of these genes are involved in the oyster's circadian clock, 2 are clock-associated genes, and 3 are light perception genes. The blue light has the most important effects on oysters' valve behavior and clock and clock-associated gene expression. Interestingly, red and green lights also show significant impacts on the daily rhythm, while the lowest impacts are shown with the green light. Finally, ALAN white light shows the same impact as the blue one in terms of loss of rhythmic oysters' percentage, but the chronobiological parameters of the remaining rhythmic oysters are less disrupted than when exposed to each of the monochromatic light's treatments alone. We conclude that ALAN's spectral composition does influence its effect on oysters' daily rhythm, which could give clues to limit physiological and ecological impacts on coastal environments.

Neurobiology and Changing Ecosystems: Mechanisms Underlying Responses to Human-Generated Environmental Impacts

Human generated environmental change profoundly affects organisms that reside across diverse ecosystems. Although nervous systems evolved to flexibly sense, respond, and adapt to environmental change, it is unclear whether the rapid rate of environmental change outpaces the adaptive capacity of complex nervous systems. Here, we explore neural systems mediating responses to, or impacted by, changing environments, such as those induced by global heating, sensory pollution, and changing habitation zones. We focus on rising temperature and accelerated changes in environments that impact sensory experience as examples of perturbations that directly or indirectly impact neural function, respectively. We also explore a mechanism involved in cross-species interactions that arises from changing habitation zones. We demonstrate that anthropogenic influences on neurons, circuits, and behaviors are widespread across taxa and require further scientific investigation to understand principles underlying neural resilience to accelerating environmental change.SIGNIFICANCE STATEMENT Neural systems evolved over hundreds of millions of years to allow organisms to sense and respond to their environments - to be receptive and responsive, yet flexible. Recent rapid, human-generated environmental changes are testing the limits of the adaptive capacity of neural systems. This presents an opportunity and an urgency to understand how neurobiological processes, including molecular, cellular, and circuit-level mechanisms, are vulnerable or resilient to changing environmental conditions. We showcase examples that range from molecular to circuit to behavioral levels of analysis across several model species, framing a broad neuroscientific approach to explore topics of neural adaptation, plasticity, and resilience. We believe this emerging scientific area is of great societal and scientific importance and will provide a unique opportunity to reexamine our understanding of neural adaptation and the mechanisms underlying neural resilience.

Dim Light at Night Promotes Circadian Disruption in Female Rats, at the Metabolic, Reproductive, and Behavioral Level

Inhabitants of urban areas are constantly exposed to light at night, which is an important environmental factor leading to circadian disruption. Streetlights filtering light through the windows and night dim light lamps are common sources of dim light at night (DLAN). The female population is susceptible to circadian disruption. The present study is aimed to determine the impact of DLAN on female Wistar rats circadian rhythms, metabolism, reproductive physiology, and behavior. After 5 weeks of DLAN exposure daily, oscillations in activity and body temperature of female rats are abolished. DLAN also decreases nocturnal food ingestion, which results in a diminishment in total food consumption. These alterations in the temporal organization of the body are associated with a significant decrease in melatonin plasmatic levels, reproductive disruptions, decreased exploration times, and marked anhedonia. This study highlights the importance of avoiding exposure to light at night, even at low intensities, to maintain the circadian organization of physiology, and denotes the great necessity of increasing the studies in females since the sexual dimorphism within the effects of desynchronizing protocols has been poorly studied.

Exploring the construction of urban artificial light ecology: a systematic review and the future prospects of light pollution

Artificial light at night (ALAN) is rapidly growing and expanding globally, posing threats to ecological safety. Urban light pollution prevention and control are moving toward urban artificial light ecology construction. To clarify the need for light ecology construction, this work analyzes 1690 articles on ALAN and light pollution and 604 on ecological light pollution from 1998 to 2022. The development process and thematic evolution of light pollution research are combed through, the historical inevitability of artificial light ecology construction is excavated, and the ecological risks of light pollution to typical animals are summarized. The results show that international research has advanced to the ecological risk factors of light pollution and the related stress mechanisms, the quantification, prediction, and pre-warning by multiple technical means, and the translation of light pollution research outcomes to prevention and control practices. While Chinese scholars have begun to pay attention to the ecological risks of light pollution, the evaluation indicators and prevention and control measures remain primarily based on human-centered needs. Therefore, a more integrated demand-side framework of light ecology construction that comprehensively considers multiple risk receptors is further constructed. Given the development trend in China, we clarified the consistency of the ecological effect of landscape lighting with landsense ecology and the consistency of light ecological risk prevention and control with the concept of One Health. Ultimately, landsense light ecology is proposed based on the "One Health" concept. This work is expected to provide a reference and inspiration for future construction of urban artificial light ecology.

Does exposure to moonlight affect day/night changes in melatonin and metabolic parameters in Amazonian fish?

Lunar cycle modulates the rhythmic activity patterns of many animals, including fish. The effect of the moonlight cycle on daily melatonin and metabolic parameters was evaluated in matrinxã (Brycon amazonicus) subjected to external natural lighting. Eighty juvenile were distributed in 4 tanks of 1m3 (20 fish/tank) and divided into two groups. One group was exposed to the full moon and the other group to the new moon for 30 days, which corresponds to the duration of the lunar period. At the end of the lunar phase, 6 fish from each group were anesthetized to collect blood, tissue and eye samples at midday and midnight. The comparison between the light and dark periods revealed a significant increase in plasma and ocular melatonin in the last period. However, there was no significant difference for plasma melatonin between moons. Ocular melatonin presented higher concentrations during the new moon. Glucose, total proteins, cortisol, liver glutathione and gill lipid peroxidation were higher in the full moon compared to in the new moon. Plasma triglyceride was higher during the night for the full moon, and the opposite was found for the new moon. Total cholesterol values were higher at night regardless the moon phase. Glutathione in the gills and lipid peroxidation in the liver showed no significant differences. These results highlight the importance of considering both the day and lunar cycles for melatonin and metabolic parameters in species of commercial interest and susceptible to stressful situations in rearing conditions.

Experimental light at night explains differences in activity onset between urban and forest great tits

Artificial light at night (ALAN) is rapidly increasing and so is scientific interest in its ecological and evolutionary consequences. In wild species, ALAN can modify and disrupt biological rhythms. However, experimental proof of such effects of ALAN in the wild is still scarce. Here, we compared diel rhythms of incubation behaviour, inferred from temperature sensors, of female great tits (Parus major) breeding in urban and forest sites. In parallel, we simulated ALAN by mounting LED lights (1.8 lx) inside forest nest-boxes, to determine the potentially causal role of ALAN affecting diel patterns of incubation. Urban females had an earlier onset of activity compared to forest females. Experimentally ALAN-exposed forest females were similar to urban females in their advanced onset of activity, compared to unexposed forest birds. However, forest females exposed to experimental ALAN, but not urban females, were more restless at night than forest control females. Our findings demonstrate that ALAN can explain the early activity timing in incubating urban great tits, but its effects on sleep disturbance in the forest are not reflected in urban females. Consequently, future research needs to address potential effects of ALAN-induced timing on individual health, fitness and population dynamics, in particular in populations that were not previously affected by light pollution.

Light pollution alters the skeletal morphology of coral juveniles and impairs their light capture capacity

Urbanization and infrastructure development have changed the night-time light regime of many coastal marine habitats. Consequently, Artificial Light at Night (ALAN) is becoming a global ecological concern, particularly in nearshore coral reef ecosystems. However, the effects of ALAN on coral architecture and their optical properties are unexplored. Here, we conducted a long-term ex situ experiment (30 months from settlement) on juvenile Stylophora pistillata corals grown under ALAN conditions using light-emitting diodes (LEDs) and fluorescent lamps, mimicking light-polluted habitats. We found that corals exposed to ALAN exhibited altered skeletal morphology that subsequently resulted in reduced light capture capacity, while also gaining better structural and optical modifications to increased light levels than their ambient-light counterparts. Additionally, light-polluted corals developed a more porous skeleton compared to the control corals. We suggest that ALAN induces light stress in corals, leading to a decrease in the solar energy available for photosynthesis during daytime illumination.

Reducing nighttime light exposure in the urban environment to benefit human health and society

Nocturnal light pollution can have profound effects on humans and other organisms. Recent research indicates that nighttime outdoor lighting is increasing rapidly. Evidence from controlled laboratory studies demonstrates that nocturnal light exposure can strain the visual system, disrupt circadian physiology, suppress melatonin secretion, and impair sleep. There is a growing body of work pointing to adverse effects of outdoor lighting on human health, including the risk of chronic diseases, but this knowledge is in a more nascent stage. In this Review, we synthesize recent research on the context-specific factors and physiology relevant to nocturnal light exposure in relation to human health and society, identify critical areas for future research, and highlight recent policy steps and recommendations for mitigating light pollution in the urban environment.

Dim light at night affects the locomotor activity of nocturnal African pygmy mice (Mus minutoides) in an intensity-dependent manner

Rodents are integral components of ecosystems as they provide several important ecosystem services. Despite their importance as prey, pollinators and seed distributors, African rodents are largely understudied. The effect of anthropogenic changes such as artificial light at night extends past urban areas to peri-urban and rural habitats, and can have profound effects on entire ecosystems. We investigated the effect of dim light at night (dLAN) on the locomotor activity rhythms of the African pygmy mouse (Mus minutoides). Pygmy mice showed a dramatic, intensity-dependent reduction in their locomotor activity when subjected to dLAN, which was accompanied by a delay in the activity onset. We also considered masking responses with a dark pulse (DP) during the day and a light pulse at night. All animals became inactive in response to a light pulse during the night, whereas approximately half of the animals showed activity during a DP in the day. Our results suggest that the African pygmy mouse is highly sensitive to light and that their activity is strongly masked by light. In their natural environment, vegetation could shield pygmy mice against high light levels; however, other anthropogenic disturbances can alter the behaviour of these animals and could affect their survival.

Endocrine effects of exposure to artificial light at night: A review and synthesis of knowledge gaps

Animals have evolved with natural patterns of light and darkness, such that light serves as an important zeitgeber, allowing adaptive synchronization of behavior and physiology to external conditions. Exposure to artificial light at night (ALAN) interferes with this process, resulting in dysregulation of endocrine systems. In this review, we evaluate the endocrine effects of ALAN exposure in birds and reptiles, identify major knowledge gaps, and highlight areas for future research. There is strong evidence for ecologically relevant levels of ALAN acting as an environmental endocrine disruptor. However, most studies focus on the pineal hormone melatonin, corticosterone release via the hypothalamus-pituitary-adrenal axis, or regulation of reproductive hormones via the hypothalamus-pituitary-gonadal axis, leaving effects on other endocrine systems largely unknown. We call for more research spanning a diversity of hormonal systems and levels of endocrine regulation (e.g. circulating hormone levels, receptor numbers, strength of negative feedback), and investigating involvement of molecular mechanisms, such as clock genes, in hormonal responses. In addition, longer-term studies are needed to elucidate potentially distinct effects arising from chronic exposure. Other important areas for future research effort include investigating intraspecific and interspecific variability in sensitivity to light exposure, further distinguishing between distinct effects of different types of light sources, and assessing impacts of ALAN exposure early in life, when endocrine systems remain sensitive to developmental programming. The effects of ALAN on endocrine systems are likely to have a plethora of downstream effects, with implications for individual fitness, population persistence, and community dynamics, especially within urban and suburban environments.

Fiat Lux: Light and Pedagogy for the 21st Century

Background

The relationship between the quality of the learning environment and student outcomes is receiving more serious attention from educational psychologists, neurologists, ophthalmologists, orthopedists, surgeons, oncologists, architects, ergonomists, nutritionists, and Michelin star chefs. There is a role for ergonomic office and school design to positively impact worker and student productivity, and one design attribute drawing attention is the indoor lit environment. In this review, we expand upon the role that light plays in education, as it has enabled millions of pupils to read at late hours, which were previously too dark. However, still unappreciated is the biological effects of artificial light on circadian rhythm and its subsequent impacts on health and learning outcomes.

Summary

This review describes the current state of light in the educational environment, its impact, and the effect of certain inexpensive and easy-to-implement adaptations to better support student growth, learning and development. We find that the current lighting environment for pupils is sub-optima based on biological mechanism and may be improved through cost effective interventions. These interventions can achieve greater biological harmonization and improve learner outcomes.

Key Message

The impact of the lighting environment in educational institutions on pupil biology has received minimal attention thus far. The current lighting environment in schools is not conducive to student health and educational performance. Cost-effective approaches can have an outsized impact on student health and educational attainment. We strongly recommend educational institutions take the lit environment into account when designing educational programs.

Ubiquitous light-emitting diodes: Potential threats to retinal circadian rhythms and refractive development

The use of light-emitting diodes (LEDs) has increased considerably in the 21st century with humans living in a modern photoperiod with brighter nights and dimmer days. Prolonged exposure to LEDs, especially at night, is considered a new source of pollution because it may affect the synthesis and secretion of retinal melatonin and dopamine, resulting in negative impacts on retinal circadian clocks and potentially disrupting retinal circadian rhythms. The control of ocular refraction is believed to be related to retinal circadian rhythms. Moreover, the global prevalence of myopia has increased at an alarming rate in recent decades. The widespread use of LEDs and the rapid increase in the prevalence of myopia overlap, which is unlikely to be a coincidence. The connection among LEDs, retinal circadian rhythms, and refractive development is both fascinating and confusing. In this review, we aim to develop a systematic framework that includes LEDs, retinal circadian rhythms and refractive development. This paper summarizes the possible mechanisms by which LEDs may disrupt retinal circadian rhythms. We propose that prolonged exposure to LEDs may induce myopia by disrupting retinal circadian rhythms. Finally, we suggest several possible countermeasures to prevent LED interference on retinal circadian rhythms, with the hope of reducing the onset and progression of myopia.

Outdoor artificial light at night and human health: A review of epidemiological studies

We conducted a non-systematic review of epidemiological studies on a potential link between exposure to outdoor artificial light at night (O-ALAN) and disease occurrence in humans published since 2009. In recent years, a number of presses have been published on this issue, but the conclusions have been mixed. We therefore decided to critically analyze the available epidemiological evidence of such a correlation. After a careful search, 51 studies were identified and included in the review. They addressed the potential link between O-ALAN exposure and the incidence of breast cancer, other cancers, sleep and circadian rhythm disorders, obesity and cardiovascular diseases, mental disorders, infectious diseases, and complications during pregnancy and childbirth. The vast majority of papers revealed the existence of such a link. However, the amount of epidemiological evidence supporting the correlation across groups of disorders varied widely. In addition, we found that all papers contained at least one of the following omissions: lack of the temporal and spatial resolution in light at night measurements, measuring only light intensity without considering its wavelength, and not accounting for many important confounding factors in their statistical analyses. Therefore, we believe that the link between O-ALAN exposure and the occurrence of the disorders in question suggested by the authors of the reviewed papers may be in some cases at least to some extent, a coincidence. Further epidemiological studies, free of significant omissions highlighted in this paper, are needed.

Behavioural drivers of ecotone exploitation: activity of groundwater animals in spring

Abstract

Border habitats such as interfaces and ecotones are promising research targets being likely areas of high species richness and genetic and phenotypic diversity. Springs are intriguing habitats exploited by both subterranean and surface species. For subterranean species, springs can provide higher trophic resources but can be risky in terms of predation and UV radiation, while for surface species, springs can be safer but less productive environments. We coupled field surveys and laboratory experiments to understand how predation risk and physical constraints, like light occurrence, affect spring exploitation by both a subterranean (Niphargus thuringius) and a surface crustacean amphipod species (Echinogammarus stammeri). From March to May 2021, we surveyed multiple springs and evaluated the activity (both during day and night) of the amphipods and of their predators. Furthermore, in a subterranean laboratory, we reared 80 N. thuringius and 80 E. stammeri under safe and risky conditions with both constant darkness and diel light variation assessing their activity and survival. Risky conditions were represented by the occurrence of meso-predators alone or coupled with the presence of a top predator. In the field, N. thuringius activity was negatively related to the density of predators, while laboratory experiments revealed a main role played by light treatments and night period. E. stammeri activity in the field was higher close to surface while in laboratory conditions decreased during time. In laboratory conditions, predation risk negatively affected survival of both amphipods. Our findings reveal that physical constraints play a key role in affecting the exploitation of ecotones and can mediate antipredator responses, thus providing selective pressures for the exploitation of border environments.

Significance statement

Understanding environmental pressures acting on ecotones is a key point to verify if new adaptations may occur at the border between two distinct habitats. Using both field and laboratory approaches, we show that, in springs, the behaviour of subterranean invertebrates is affected by surface physical constraints which can mediate the effects of predation risk. Behavioural strategies to avoid predation, such as nocturnal activity, may promote spring ecotone exploitation by groundwater animals, such as amphipod crustaceans.

A flashing light may not be that flashy: A systematic review on critical fusion frequencies

BACKGROUND

Light pollution could represent one of the main drivers behind the current biodiversity erosion. While the effects of many light components on biodiversity have already been studied, the influence of flicker remains poorly understood. The determination of the threshold frequency at which a flickering light is perceived as continuous by a species, usually called the Critical Fusion Frequency (CFF), could thus help further identify the impacts of artificial lighting on animals.

OBJECTIVE

This review aimed at answering the following questions: what is the distribution of CFF between species? Are there differences in how flicker is perceived between taxonomic classes? Which species are more at risk of being impacted by artificial lighting flicker?

METHODS

Citations were extracted from three literature databases and were then screened successively on their titles, abstracts and full-texts. Included studies were critically appraised to assess their validity. All relevant data were extracted and analysed to determine the distribution of CFF in the animal kingdom and the influence of experimental designs and species traits on CFF.

RESULTS

At first, 4881 citations were found. Screening and critical appraisal provided 200 CFF values for 156 species. Reported values of CFF varied from a maximum of between 300 Hz and 500 Hz for the beetle Melanophila acuminata D. to a mean of 0.57 (± 0.08) Hz for the snail Lissachatina fulica B. Insects and birds had higher CFF than all other studied taxa. Irrespective of taxon, nocturnal species had lower CFF than diurnal and crepuscular ones.

CONCLUSIONS

We identified nine crepuscular and nocturnal species that could be impacted by the potential adverse effects of anthropogenic light flicker. We emphasize that there remains a huge gap in our knowledge of flicker perception by animals, which could potentially be hampering our understanding of its impacts on biodiversity, especially in key taxa like bats, nocturnal birds and insects.

Neurobiology and changing ecosystems: Toward understanding the impact of anthropogenic influences on neurons and circuits

Rapid anthropogenic environmental changes, including those due to habitat contamination, degradation, and climate change, have far-reaching effects on biological systems that may outpace animals' adaptive responses. Neurobiological systems mediate interactions between animals and their environments and evolved over millions of years to detect and respond to change. To gain an understanding of the adaptive capacity of nervous systems given an unprecedented pace of environmental change, mechanisms of physiology and behavior at the cellular and biophysical level must be examined. While behavioral changes resulting from anthropogenic activity are becoming increasingly described, identification and examination of the cellular, molecular, and circuit-level processes underlying those changes are profoundly underexplored. Hence, the field of neuroscience lacks predictive frameworks to describe which neurobiological systems may be resilient or vulnerable to rapidly changing ecosystems, or what modes of adaptation are represented in our natural world. In this review, we highlight examples of animal behavior modification and corresponding nervous system adaptation in response to rapid environmental change. The underlying cellular, molecular, and circuit-level component processes underlying these behaviors are not known and emphasize the unmet need for rigorous scientific enquiry into the neurobiology of changing ecosystems.

Effect of artificial light at night on sleep and metabolism in weaver birds

Artificial light at night is constantly minimizing the span of dark nights from the natural light-dark cycle of earth. Over the past century, the "lightscape" of earth has completely changed owing to technological advancements which subsequently changed the lifestyle of human as well as the nearby animal species. This motivated the present study, wherein we investigated the impact of light at night (LAN) on behavior and physiology of a diurnal passerine finch, baya weaver (Ploceus philippinus). A group of bird (N=10) exposed to 12L:12D photoperiod was initially subjected to dark nights (0 lux) for a period of 1.5 weeks followed by 5 lux, night light for a span of 4 weeks. The first week in LAN served as acute treatment with respect to the fourth week (chronic). The results reveal significant increase in nighttime activity and sleep loss with respect to acute LAN, while significant inclusion of drowsiness behavior during the day in response to chronic LAN. Besides these behavioral alterations, changes in physiological parameters such as reduction in body mass, loss of gradient between pre- and post- prandial blood glucose levels, and elevation in plasma corticosterone levels were more prominent during acute exposure of LAN. Plasma metabolites such as triglycerides, total protein, serum glutamic-oxaloacetic transaminase (SGOT), and creatinine concentrations also hiked in response to acute LAN treatment. Thus, acute exposure of LAN seems to serve as a novel environment for the bird leading to more pronounced impacts on behavioral and physiological observations during the experiment. In chronic exposure, the birds sort of adapted themselves to the prevailing circumstances as evident by decreased nighttime activity, rebound of sleep and corticosterone levels, etc. Thus, the study clearly demonstrates the differential impact of acute and chronic exposure of LAN on behavior and physiology of birds.

Harbours as unique environmental sites of multiple anthropogenic stressors on fish hormonal systems

Fish development and acclimation to environmental conditions are strongly mediated by the hormonal endocrine system. In environments contaminated by anthropogenic stressors, hormonal pathway alterations can be detrimental for growth, survival, fitness, and at a larger scale for population maintenance. In the context of increasingly contaminated marine environments worldwide, numerous laboratory studies have confirmed the effect of one or a combination of pollutants on fish hormonal systems. However, this has not been confirmed in situ. In this review, we explore the body of knowledge related to the influence of anthropogenic stressors disrupting fish endocrine systems, recent advances (focusing on thyroid hormones and stress hormones such as cortisol), and potential research perspectives. Through this review, we highlight how harbours can be used as "in situ laboratories" given the variety of anthropogenic stressors (such as plastic, chemical, sound, light pollution, and invasive species) that can be simultaneously investigated in harbours over long periods of time.

Association between bedroom light exposure at night and allostatic load among Chinese young adults

Light at night (LAN) has received increasing attention for its potential health hazards to human and animals. However, to our knowledge, no study has explored the specific effects of bedroom nighttime light exposure on allostatic load (AL). To investigate the association between bedroom individual-level LAN exposure and AL among young adults, an integrative index manifests multiple system dysregulation. Using data from a cohort of 484 Chinese young adults aged 16-22 years. Bedroom light was objectively recorded at 1-min intervals for two nights using a portable illuminance meter. Fasting blood samples were collected at one-year follow-up for the detection of AL parameters. AL score was derived as sum of the top quartile of twelve physiological biomarkers in four systems: metabolic system (BMI, WC, TC, HDL, LDL, TG, HbA1c, INS, GLU); cardiovascular system (SBP, DBP); immune and inflammatory systems (hs-CRP), with HDL was lowest quartile. Univariate and multivariate linear regression models were used to evaluate the association between LAN intensity with AL score and separate AL parameters. The average age of subjects was 18.7 years, 64.3% were female. The mean AL score of LAN group (average LAN intensity ≥ 3lx) was significantly higher than Dim group (3.6 ± 2.6 vs. 2.7 ± 2.1; P = 0.007). For each 1 lx increase of LAN intensity was associated with 0.15-unit increase in AL score (95% CI: 0.06, 0.24; P = 0.001). Moreover, LAN group was associated with increased 1.01-unit in AL score (95% CI: 0.36-1.66; P = 0.003) compared to Dim group. Significant associations between bedroom LAN exposure with allostatic load and separate AL biomarkers were observed in our study. Keeping bedroom darkness at night may be a practicable option to reduce the wear of multiple body systems and improve human cardiometabolic health from early in life.

The Effects of Artificial Night Lighting on Tail Regeneration and Prey Consumption in a Nocturnal Salamander (Plethodon cinereus) and on the Behavior of Fruit Fly Prey (Drosophila virilis)

Simple Summary

Amphibians, including salamanders, are declining worldwide at an alarming rate due to a variety of factors that include habitat decline and destruction and environmental pollutants. Artificial light at night (ALAN) due to human activities is a nearly ubiquitous pollutant and can have serious consequences for amphibians. We examined the impact of ecologically-relevant levels of ALAN on tail regeneration in the eastern red-backed salamander, prey consumption by these salamanders and behavior of their fruit fly prey. We found that ALAN reduced the rate of salamander tail regeneration at some light levels above the naturally dark nocturnal illumination and increased the activity of their prey but not always in a simple, linear fashion. Thus, ALAN, even at very low levels, can influence the physiology and regeneration of a nocturnal salamander.

Abstract

As human development continues to encroach into natural habitats, artificial light at night (ALAN) has increasingly become a concern for wildlife. Nocturnal animals are especially vulnerable to ALAN, as the physiology and behavior of nocturnal species have evolved under conditions associated with predictably dark environments. Studies exposing amphibians to constant bright light provide evidence for changes to normal metabolism, growth, and behavior, but few of these studies have used treatments of dim ALAN comparable to that found in affected habitats. Eastern red-backed salamanders, Plethodon cinereus, use their tails for fat storage and communication, are capable of tail autotomy as an antipredator mechanism, and can regenerate the tail in its entirety. We examined the effect of different, ecologically-relevant intensities of ALAN on the rate of tail regeneration in adult P. cinereus. We hypothesized that ALAN would increase tail regeneration rates such that salamanders exposed to higher levels of light at night would regenerate tails faster than those exposed to lower light levels. In a controlled laboratory setting, we exposed salamanders (N = 76) in test chambers to nocturnal illuminations of 0.0001 lx (no ALAN, natural nocturnal illumination dark control), 0.01 lx (weak ALAN), 1 lx (moderate ALAN), or 100 lx (bright ALAN, equal to dim daytime and our day lighting treatment) for a period of 90 d immediately following tail autotomy. In addition, because these salamanders eat mostly live, moving prey, we investigated the impact of ALAN on the behavior of prey (Drosophila virilis) fed to the salamanders in our laboratory trials, which could alter feeding and regeneration rates in salamanders. We predicted that prey consumption would not be affected by ALAN and measured both prey consumption and prey behavior (activity) to examine the potential influence on regeneration. For tail regeneration, we found a non-monotonic response to ALAN, with salamanders exposed to nocturnal illuminations 0.1 lx and 100 lx regenerating tails significantly slower than salamanders in the 0.0001 lx or 1 lx treatments. Prey consumption did not differ among light treatments; however, fruit fly activity increased with increasing ALAN. These results suggest that ALAN influences regeneration rates, but the rate of regeneration is not dose-dependent and is not explained easily by prey consumption or movement of prey. We suggest that tail regeneration in these salamanders may involve a complex mechanism of altered gene expression and/or modulation of hormonal activity (corticosterone, melatonin, serotonin, and/or prolactin) at different intensities of nocturnal lighting.

Automated analysis of activity, sleep, and rhythmic behaviour in various animal species with the Rtivity software

Behavioural studies provide insights into normal and disrupted biological mechanisms. In many research areas, a growing spectrum of animal models—particularly small organisms—is used for high-throughput studies with infrared-based activity monitors, generating counts per time data. The freely available software to analyse such data, however, are primarily optimized for drosophila and circadian analysis. Researchers investigating other species or non-circadian behaviour would thus benefit from a more versatile software. Here we report the development of a free and open-source software—Rtivity—allowing customisation of species-specific parameters, and offering a versatile analysis of behavioural patterns, biological rhythms, stimulus responses, and survival. Rtivity is based on the R language and uses Shiny and the recently developed Rethomics package for a user-friendly graphical interface without requiring coding skills. Rtivity automatically assesses survival, computes various activity, sleep, and rhythmicity parameters, and performs fractal analysis of activity fluctuations. Rtivity generates multiple informative graphs, and exports structured data for efficient interoperability with common statistical software. In summary, Rtivity facilitates and enhances the versatility of the behavioural analysis of diverse animal species (e.g. drosophila, zebrafish, daphnia, ants). It is thus suitable for a broad range of researchers from multidisciplinary fields such as ecology, neurobiology, toxicology, and pharmacology.

Exposure to bedroom light pollution and cardiometabolic risk: A cohort study from Chinese young adults

Indoor light environment has altered dramatically and exposure to light at night (LAN) potential leads to the progression of cardiometabolic conditions. However, few studies have investigated the effect of bedroom LAN exposure on cardiometabolic risk. To estimate the associations between multi-period bedroom LAN exposure with cardiometabolic risk among Chinese young adults. We objectively measured multi-period bedroom LAN intensity using portable illuminance meter in an ongoing prospective cohort (n = 484). At one-year follow-up, 230 young adults provided fasting blood samples for quantification of cardiometabolic parameters. Cardiometabolic (CM)-risk score was derived as the sum of standardized sex-specific z-scores for waist circumference (WC), mean arterial pressure (MAP), high-density lipoprotein cholesterol (HDL-C), triglyceride (TG) and homeostasis model assessment for insulin resistance (HOMA-IR), with HDL-C multiplied by - 1. Multivariate and univariable linear regression models were used to examine associations of multi-period bedroom LAN exposure with cardiometabolic risk. Exposure to higher bedroom LAN intensity is associated with 1.47-unit increase in CM-risk score (95% CI: 0.69-2.25; P < 0.001). Besides, post-bedtime light exposure was associated with elevated fasting insulin (PBL-1h: β = 0.06, 95% CI: 0.01-0.10; PBL-4h: β = 0.33, 95% CI: 0.19-0.47) and HOMA-IR (PBL-1h: β = 0.013, 95% CI: 0-0.03; PBL-4h: β = 0.07, 95% CI: 0.04-0.11) while pre-awake light exposure was associated with elevated total cholesterol (PAL-1h: β = 0.03, 95% CI: 0.02-0.04; PAL-2h: β = 0.02, 95% CI: 0.01-0.03), triglyceride (PAL-1h: β = 0.015, 95% CI: 0.01-0.02; PAL-2h: β = 0.01, 95% CI: 0-0.02) and low-density lipoprotein cholesterol (PAL-1h: β = 0.02, 95% CI: 0.01-0.03; PAL-2h: β = 0.02, 95% CI: 0.01-0.03). Among young adults, bedroom LAN exposure was significantly associated with higher cardiometabolic risk. Furthermore, different periods of bedroom light exposure have time-dependent effect on cardiometabolic risk. Further research is needed to confirm our findings and to elucidate potential mechanisms.

Integrated molecular and behavioural data reveal deep circadian disruption in response to artificial light at night in male Great tits (Parus major)

Globally increasing levels of artificial light at night (ALAN) are associated with shifting rhythms of behaviour in many wild species. However, it is unclear whether changes in behavioural timing are paralleled by consistent shifts in the molecular clock and its associated physiological pathways. Inconsistent shifts between behavioural and molecular rhythms, and between different tissues and physiological systems, disrupt the circadian system, which coordinates all major body functions. We therefore compared behavioural, transcriptional and metabolomic responses of captive great tits (Parus major) to three ALAN intensities or to dark nights, recording activity and sampling brain, liver, spleen and blood at mid-day and midnight. ALAN advanced wake-up time, and this shift was paralleled by advanced expression of the clock gene BMAL1 in all tissues, suggesting close links between behaviour and clock gene expression across tissues. However, further analysis of gene expression and metabolites revealed that clock shifts were inconsistent across physiological systems. Untargeted metabolomic profiling showed that only 9.7% of the 755 analysed metabolites followed the behavioural shift. This high level of desynchronization indicates that ALAN disrupted the circadian system on a deep, easily overlooked level. Thus, circadian disruption could be a key mediator of health impacts of ALAN on wild animals.