Constant illumination reduces circulating melatonin and impairs immune function in the cricket Teleogryllus commodus

When night becomes day: Artificial light at night alters insect behavior under semi-natural conditions

Light is the most important Zeitgeber for temporal synchronization in nature. Artificial light at night (ALAN) disrupts the natural light-dark rhythmicity and thus negatively affects animal behavior. However, to date, ALAN research has been mostly conducted under laboratory conditions in this context. Here, we used the field cricket, Gryllus bimaculatus, to investigate the effect of ALAN on insect behavior under semi-natural conditions, i.e., under shaded natural lighting conditions, natural temperature and soundscape. Male crickets were placed individually in outdoor enclosures and exposed to ALAN conditions ranging from <0.01 to 1500 lx intensity. The crickets' stridulation behavior was recorded for 14 consecutive days and nights and their daily activity patterns were analysed. ALAN impaired the crickets' stridulation rhythm, evoking a change in the crickets' naturally synchronized daily activity period. This was manifested by a light-intensity-dependent increase in the proportion of insects demonstrating an intrinsic circadian rhythm (free-run behavior). This also resulted in a change in the population's median activity cycle period. These ALAN-induced effects occurred despite the crickets' exposure to almost natural conditions. Our findings provide further validity to our previous studies on ALAN conducted under lab conditions and establish the deleterious impacts of ALAN on animal behavioral patterns. TEASER: Artificial light at night alters cricket behavior and desynchronizes their stridulation even under near-natural conditions.

Crickets in the spotlight: exploring the impact of light on circadian behavior

Crickets serve as a well-established model organism in biological research spanning various fields, such as behavior, physiology, neurobiology, and ecology. Cricket circadian behavior was first reported over a century ago and prompted a wealth of studies delving into their chronobiology. Circadian rhythms have been described in relation to fundamental cricket behaviors, encompassing stridulation and locomotion, but also in hormonal secretion and gene expression. Here we review how changes in illumination patterns and light intensity differentially impact the different cricket behaviors as well as circadian gene expression. We further describe the cricket's circadian pacemaker. Ample anatomical manipulations support the location of a major circadian pacemaker in the cricket optic lobes and another in the central brain, possibly interconnected via signaling of the neuropeptide PDF. The cricket circadian machinery comprises a molecular cascade based on two major transcriptional/translational negative feedback loops, deviating somewhat from the canonical model of Drosophila and emphasizing the significance of exploring alternative models. Finally, the nocturnal nature of crickets has provided a unique avenue for investigating the repercussions of artificial light at night on cricket behavior and ecology, underscoring the critical role played by natural light cycles in synchronizing cricket behaviors and populations, further supporting the use of the cricket model in the study of the effects of light on insects. Some gaps in our knowledge and challenges for future studies are discussed.

Spectral composition of light-emitting diodes impacts aquatic and terrestrial invertebrate communities with potential implications for cross-ecosystem subsidies

Resource exchanges in the form of invertebrate fluxes are a key component of aquatic-terrestrial habitat coupling, but this interface is susceptible to human activities, including the imposition of artificial light at night. To better understand the effects of spectral composition of light-emitting diodes (LEDs)-a technology that is rapidly supplanting other lighting types-on emergent aquatic insects and terrestrial insects, we experimentally added LED fixtures that emit different light spectra to the littoral zone and adjacent riparian habitat of a pond. We installed four replicate LED treatments of different wavelengths (410, 530 and 630 nm), neutral white (4000 k) and a dark control, and sampled invertebrates in both terrestrial and over-water littoral traps. Invertebrate communities differed among light treatments and between habitats, as did total insect biomass and mean individual insect size. Proportional allochthonous biomass was greater in the riparian habitat and among some light treatments, demonstrating an asymmetrical effect of differently coloured LEDs on aquatic-terrestrial resource exchanges. Overall, our findings demonstrate that variation in wavelength from LEDs may impact the flux of resources between systems, as well as the communities of insects that are attracted to particular spectra of LED lighting, with probable implications for consumers. This article is part of the theme issue 'Light pollution in complex ecological systems'.

Circadian lifestyle determinants of immune checkpoint inhibitor efficacy

Immune Checkpoint Inhibitors (ICI) have revolutionised cancer care in recent years. Despite a global improvement in the efficacy and tolerability of systemic anticancer treatments, a sizeable proportion of patients still do not benefit maximally from ICI. Extensive research has been undertaken to reveal the immune- and cancer-related mechanisms underlying resistance and response to ICI, yet more limited investigations have explored potentially modifiable lifestyle host factors and their impact on ICI efficacy and tolerability. Moreover, multiple trials have reported a marked and coherent effect of time-of-day ICI administration and patients' outcomes. The biological circadian clock indeed temporally controls multiple aspects of the immune system, both directly and through mediation of timing of lifestyle actions, including food intake, physical exercise, exposure to bright light and sleep. These factors potentially modulate the immune response also through the microbiome, emerging as an important mediator of a patient's immune system. Thus, this review will look at critically amalgamating the existing clinical and experimental evidence to postulate how modifiable lifestyle factors could be used to improve the outcomes of cancer patients on immunotherapy through appropriate and individualised entrainment of the circadian timing system and temporal orchestration of the immune system functions.

Artificial light at night promotes bottom-up changes in a woodland food chain

Artificial light at night (ALAN) is a recognised disruptor of biological function and ecological communities. Despite increasing research effort, we know little regarding the effect of ALAN on woody plants, including trees, or its indirect effects on their colonising invertebrates. These effects have the potential to disrupt woodland food webs by decreasing the productivity of invertebrates and their secretions, including honeydew and lerps, with cascading effects on other fauna. Here, we cultivated juvenile river red gums (Eucalyptus camaldulensis) for 40 weeks under experimentally manipulated light (ALAN) or naturally dark (control) conditions. To assess direct impacts on tree growth, we took multiple measures of growth at four time periods, and also measured physiological function, biomass and investment in semi-mature trees. To assess experimentally the direct and indirect (tree-mediated) impacts of ALAN on invertebrates, from 19 weeks onwards, we matched and mismatched trees with their original ALAN environments. We colonised trees with a common herbivore of E. camaldulensis, the red gum lerp psyllid (Glycaspis nr. brimblecombei) and then measured the effects of current and historic tree lighting treatment on the psyllid life cycle. Our data revealed direct effects of ALAN on tree morphology: E. camaldulensis trees exposed to ALAN shifted biomass allocation away from roots and into leaves and increased specific leaf area. However, while the intensity of ALAN was sufficient to promote photosynthesis (net carbon gain) at night, this did not translate into variation in tree water status or photosystem adaptation to dim night-time light for ALAN-exposed trees. We found some evidence that ALAN had broad-scale community effects-psyllid nymphs colonising ALAN trees produced more lerps-but we found no other direct or indirect impacts of ALAN on the psyllid life cycle. Our results suggest that trees exposed to ALAN may share morphological responses with trees under dim daylight conditions. Further, ALAN may have significant 'bottom-up' effects on Eucalyptus woodland food webs through both trees and herbivores, which may impact higher trophic levels including woodland birds, mammals and invertebrates.

Transcriptional Response of Circadian Clock Genes to an ‘Artificial Light at Night’ Pulse in the Cricket Gryllus bimaculatus

Light is the major signal entraining the circadian clock that regulates physiological and behavioral rhythms in most organisms, including insects. Artificial light at night (ALAN) disrupts the natural light–dark cycle and negatively impacts animals at various levels. We simulated ALAN using dim light stimuli and tested their impact on gene expression in the cricket Gryllus bimaculatus, a model of insect physiology and chronobiology. At night, adult light–dark-regime-raised crickets were exposed for 30 min to a light pulse of 2–40 lx. The relative expression of five circadian-clock-associated genes was compared using qPCR. A dim ALAN pulse elicited tissue-dependent differential expression in some of these genes. The strongest effect was observed in the brain and in the optic lobe, the cricket’s circadian pacemaker. The expression of opsin-Long Wave (opLW) was upregulated, as well as cryptochrome1-2 (cry) and period (per). Our findings demonstrate that even a dim ALAN exposure may affect insects at the molecular level, underscoring the impact of ALAN on the circadian clock system.

Light at night disrupts biological clocks, calendars, and immune function

Light at night is a pervasive problem in our society; over 80% of the world’s population experiences significant light pollution. Exacerbating this issue is the reality that artificially lit outdoor areas are growing by 2.2% per year and continuously lit areas brighten by 2.2% each year due to the rapid growths in population and urbanization. Furthermore, the increase in the prevalence of night shift work and smart device usage contributes to the inescapable nature of artificial light at night (ALAN). Although previously assumed to be innocuous, ALAN has deleterious effects on the circadian system and circadian-regulated physiology, particularly immune function. Due to the relevance of ALAN to the general population, it is important to understand its roles in disrupting immune function. This review presents a synopsis of the effects of ALAN on circadian clocks and immune function. We delineate the role of ALAN in altering clock gene expression and suppressing melatonin. We review the effects of light at night on inflammation and the innate and adaptive immune systems in various species to demonstrate the wide range of ALAN consequences. Finally, we propose future directions to provide further clarity and expansion of the field.

Litopenaeus vannamei BMAL1 Is a Critical Mediator Regulating the Expression of Glucose Transporters and Can Be Suppressed by Constant Darkness

Simple Summary

Growing evidence has indicated that glucose absorption exhibits profound circadian rhythmicity, mediated entirely by glucose transporters. We observed that the daily profile of BMAL1, GLUT1 and SGLT1 expression was also synchronized in the intestine and the hepatopancreas of Litopenaeus vannamei. Our result identified for the first time that BMAL1 is a critical mediator regulating the expression of glucose transporters, which could be suppressed by constant darkness in L. vannamei.

Abstract

Aryl hydrocarbon receptor nuclear translocator-like protein 1 (BMAL1) is a core circadian transcription factor that controls the 24-h cycle of physiological processes. In shrimp, the role of BMAL1 in the regulating glucose metabolism remains unclear. Firstly, we observed that the daily profile of BMAL1, GLUT1 and SGLT1 expression were synchronized in the intestine and the hepatopancreas of Litopenaeus vannamei. Then we examined the effects of BMAL1 on the gene expression of glucose transporter type 1 (SGLT1) and sodium-glucose cotransporter 1 (GLUT1) in vivo and in vitro. BMAL1 in L. vannamei shares 70.91–96.35% of sequence identities with other shrimp species and possesses the conserved helix-loop-helix domain and polyadenylation site domain. The in vitro dual-luciferase reporter assay and in vivo RNA interference experiment demonstrated that BMAL1 exerted a positive regulation effect on the expression of glucose transporters in L. vannamei. Moreover, we conducted an eight-week treatment to investigate whether light/dark cycle change would influence growth performance, and gene expression of BMAL1, GLUT1 and SGLT1 in L. vannamei. Our result showed that compared with natural light treatment, constant darkness (24-h darkness) significantly decreased (p < 0.05) serum glucose concentration, and suppressed (p < 0.05) the gene expression of BMAL1, GLUT1 and SGLT1 in the hepatopancreas and the intestine. Growth performance and survival rate were also decreased (p < 0.05) by constant darkness treatment. Our result identified BMAL1 as a critical mediator regulating the expression of glucose transporters, which could be suppressed by constant darkness in L. vannamei. It would be quite interesting to explore the mechanism of dark/light cycles on glucose transport and metabolism in L. vannamei, which might provide a feeding strategy for improving carbohydrate utilization in the future.

Effects of artificial light at night (ALAN) on gene expression of Aquatica ficta firefly larvae

Artificial light at night (ALAN) is a major driver of firefly population declines, but its physiological effects are not well understood. To investigate the impact of ALAN on firefly development, we exposed larval Aquatica ficta fireflies to ALAN for two weeks. High larval mortality was observed in the periods of 1-68 days and 106-134 days post-treatment, which may represent the short- and long-term impacts of ALAN. We then profiled the transcriptome of larval Aquatica ficta fireflies following two weeks of ALAN exposure. A total of 1262 (1.67% out of 75777 unigenes) were differentially expressed in the treatment group: 1157 were down-regulated, and 105 were up-regulated. Up-regulated unigenes were related to regulation of hormone levels, ecdysteroid metabolic process, and response to stimulus; down-regulated unigenes were related to negative regulation of insulin receptor signaling, germ cell development, oogenesis, spermatid development, and regulation of neuron differentiation. Transcriptome results suggest that the endocrine, reproductive, and neural development of firefly larvae could be impaired by even relatively brief period of ALAN exposure. This report contributes a much-needed molecular perspective to the growing body of research documenting the fitness impacts of ALAN on bioluminescent fireflies.

Artificial light at night alters the seasonal responses of biting mosquitoes

Urban light pollution caused by artificial light at night (ALAN) profoundly affects the ecology, behavior, and physiology of plants and animals. Further, this widespread environmental pollutant has the potential to negatively impact human and animal health by changing the seasonal dynamics of disease-transmitting insects. In response to short days, females of the Northern house mosquito enter an overwintering dormancy, or diapause. While in diapause, female mosquitoes divert energy away from reproduction, cease blood-feeding, and no longer transmit disease. We demonstrate that exposure to dim ALAN (~4 lx) causes female mosquitoes to avert diapause and become reproductively active, as these females acquired less fat content, developed larger egg follicles, imbibed vertebrate blood, and produced viable eggs and larvae. Our findings suggest that mosquitoes in highly light-polluted areas such as cities may be actively reproducing and biting later in the season, thereby extending the period of disease risk for urban residents. Our results suggest that ALAN should be considered when modeling mosquito abundance, disease risk, and when deciding how long mosquito surveillance and control should persist in temperate regions.

Can skyglow reduce nocturnal melatonin concentrations in Eurasian perch?

Artificial light at night (ALAN) changes the natural rhythm of light and darkness and can impair the biorhythms of animals, for example the nocturnal melatonin production of vertebrates, which serves as a proxy for daily physiological rhythms. Freshwater fish are exposed to ALAN in large urban and suburban areas in the form of direct light or in the form of skyglow, a diffuse brightening of the night sky through the scattered light reflected by clouds, atmospheric molecules, and particles in the air. However, investigations on the sensitivity of melatonin production of fish towards low intensities of ALAN in the range of typical skyglow are rare. Therefore, we exposed Eurasian perch (Perca fluviatilis) to nocturnal illumination levels of 0.01 lx, 0.1 lx and 1 lx and a control group with dark nights and daylight intensities of 2900 lx in all groups. After ten days of exposure to the experimental conditions, tank water was non-invasively sampled every 3 h over a 24 h period and melatonin was measured by ELISA. Melatonin was gradually reduced in all treatments with increasing intensity of ALAN whereas rhythmicity was maintained in all treatment groups although at 1 lx not all evaluated parameters confirmed rhythmicity. These results show a high sensitivity of Eurasian perch towards ALAN indicating that low light intensities of 0.01 lx and 0.1 lx as they occur in urban and suburban areas in the form of skyglow can affect the physiology of Eurasian perch. Furthermore, we highlight how this may impact perch in their sensitivity towards lunar rhythms and the role of skyglow for biorhythms of temperate freshwater fish.

Dim artificial light at night reduces the cellular immune response of the black field cricket, Teleogryllus commodus

A functioning immune system is crucial for protection against disease and illness, yet increasing evidence suggests that species living in urban areas could be suffering from immune suppression, due to the presence of artificial light at night (ALAN). This study examined the effects of ecologically relevant levels of ALAN on three key measures of immune function (haemocyte concentration, lytic activity, and phenoloxidase activity) using a model invertebrate species, the Australian black field cricket, Teleogryllus commodus. We reared crickets under an ecologically relevant daily light-cycle consisting of 12 hr bright daylight (2600 lx) followed by either 12 h darkness (0 lx) or dim environmentally relevant ALAN (1, 10, 100 lx), and then assessed immune function at multiple time points throughout adult life using haemolymph samples. We found that the presence of ALAN had a clear negative effect on haemocytes, while the effects on lytic activity and phenoloxidase activity were more complex or largely unaffected by ALAN. Furthermore, the effects of lifelong exposure to ALAN of 1 lx were comparable to those of 10 and 100 lx. Our data suggest that the effects of ALAN could be large and widespread, and such reductions in the core immune response of individuals will likely have greater consequences for fitness and survival under more malign conditions, such as those of the natural environment.

Switching LPS to LED Streetlight May Dramatically Reduce Activity and Foraging of Bats

Artificial light at night is considered a major threat to biodiversity, especially for nocturnal species, as it reduces habitat availability, quality, and functionality. Since the recent evolution in light technologies in improving luminous efficacy, developed countries are experiencing a renewal of their lighting equipment that reaches its end-of-life, from conventional lighting technologies to light emitting diodes (LEDs). Despite potential cascading impacts of such a shift on nocturnal fauna, few studies have so far dealt with the impact of the renewal of street lighting by new technologies. Specifically, only one study, by Rowse et al.2016, examined the effects of switching from widely used low pressure sodium (LPS) lamps to LEDs, using bats as biological models. This study was based on a before-after-control-impact paired design (BACIP) at 12 pairs in the UK, each including one control and one experimental streetlight. If Rowse et al. 2016 showed no effect of switching to LEDs streetlights on bat activity, the effects of respective changes in light intensity and spectrum were not disentangled when testing switch effects. Here, we conduct a retrospective analysis of their data to include these covariates in statistical models with the aim of disentangling the relative effects of these light characteristics. Our re-analysis clearly indicates that the switches in spectrum and in intensity with replacement of LPS with LED lamps have significant additive and interactive effects, on bat activity. We also show that bat activity and buzz ratio decrease with increasing LED intensity while an opposite effect is observed with LPS lamps. Hence, the loss or the gain in bat activity when lamp types, i.e., spectrum, are switched strongly depends on the initial and new lamp intensities. Our results stress the need to consider simultaneously the effects of changes in the different lights characteristics when street lighting changes. Because switches from LPS to LED lamps can lead to an increase in light intensity, such technological changes may involve a reduction of bat activity in numerous cases, especially at high LED intensities. Since we are currently at an important crossroad in lighting management, we recommend to limit LED intensity and improve its spectral composition toward warmer colors to limit potential deleterious impacts on bat activity.

Working with Inadequate Tools: Legislative Shortcomings in Protection against Ecological Effects of Artificial Light at Night

The fundamental change in nocturnal landscapes due to the increasing use of artificial light at night (ALAN) is recognized as being detrimental to the environment and raises important regulatory questions as to whether and how it should be regulated based on the manifold risks to the environment. Here, we present the results of an analysis of the current legal obligations on ALAN in context with a systematic review of adverse effects. The legal analysis includes the relevant aspects of European and German environmental law, specifically nature conservation and immission control. The review represents the results of 303 studies indicating significant disturbances of organisms and landscapes. We discuss the conditions for prohibitions by environmental laws and whether protection gaps persist and, hence, whether specific legislation for light pollution is necessary. While protection is predominantly provided for species with special protection status that reveal avoidance behavior of artificially lit landscapes and associated habitat loss, adverse effects on species and landscapes without special protection status are often unaddressed by existing regulations. Legislative shortcomings are caused by difficulties in proving adverse effect on the population level, detecting lighting malpractice, and applying the law to ALAN-related situations. Measures to reduce ALAN-induced environmental impacts are highlighted. We discuss whether an obligation to implement such measures is favorable for environmental protection and how regulations can be implemented.

Orb-weaving spiders are fewer but larger and catch more prey in lit bridge panels from a natural artificial light experiment

Artificial light at night is rapidly changing the sensory world. While evidence is accumulating for how insects are affected, it is not clear how this impacts higher trophic levels that feed on insect communities. Spiders are important insect predators that have recently been shown to have increased abundance in urban areas, but have shown mixed responses to artificial light. On a single bridge with alternating artificially lit and unlit sections, I measured changes in the orb-weaving spider Larinioides sclopetarius (Araneidae) web abundance, web-building behavior, prey-capture, and body condition. In artificially lit conditions, spiders caught more prey with smaller webs, and had higher body conditions. However, there were fewer spiders with active webs in those lit areas. This suggests that either spiders were not taking advantage of an ecological insect trap, perhaps due to an increased risk of becoming prey themselves, or were satiated, and thus not as active within these habitats. The results from this natural experiment may have important consequences for both insects and spiders in urban areas under artificial lighting conditions.

Long-Term Comparison of Attraction of Flying Insects to Streetlights after the Transition from Traditional Light Sources to Light-Emitting Diodes in Urban and Peri-Urban Settings

Among the different light sources used for street lighting, light-emitting diodes (LEDs) are likely to dominate the world market in the coming years. At the same time, the spectral composition of nocturnal illumination is changing. Europe and many other areas worldwide have implemented bans on energy-inefficient lamps, such as the still very common mercury vapor lamps. However, the impact of artificial light on insects is mostly tested with light-traps or flight-intercept traps that are used for short periods only. By comparing the numbers of insects attracted by street lamps before and after replacing mercury vapor light sources (MV) with light emitting diodes, we assessed the impact in more typical (urban and peri-urban) settings over several years. We found that LED attracted approximately half of the number of insects compared to MV lights. Furthermore, most insect groups are less drawn by LED than by MV, while Hymenoptera are less attracted by MV than by LED. Thus, the composition of the attracted communities differed between the light sources, which may impact ecosystem processes and functions. In green peri-urban settings more insects are attracted than in an urban setting, but the relative difference between the light sources is the same.

Artificial light at night alters life history in a nocturnal orb-web spider

The prevalence of artificial light at night (ALAN) is increasing rapidly around the world. The potential physiological costs of this night lighting are often evident in life history shifts. We investigated the effects of chronic night-time exposure to ecologically relevant levels of LED lighting on the life history traits of the nocturnal Australian garden orb-web spider (Eriophora biapicata). We reared spiders under a 12-h day and either a 12-h natural darkness (∼0 lux) or a 12-h dim light (∼20 lux) night and assessed juvenile development, growth and mortality, and adult reproductive success and survival. We found that exposure to ALAN accelerated juvenile development, resulting in spiders progressing through fewer moults, and maturing earlier and at a smaller size. There was a significant increase in daily juvenile mortality for spiders reared under 20 lux, but the earlier maturation resulted in a comparable number of 0 lux and 20 lux spiders reaching maturity. Exposure to ALAN also considerably reduced the number of eggs produced by females, and this was largely associated with ALAN-induced reductions in body size. Despite previous observations of increased fitness for some orb-web spiders in urban areas and near night lighting, it appears that exposure to artificial night lighting may lead to considerable developmental costs. Future research will need to consider the detrimental effects of ALAN combined with foraging benefits when studying nocturnal insectivores that forage around artificial lights.

Effects of light at night on laboratory animals and research outcomes

Light has substantial influences on the physiology and behavior of most laboratory animals. As such, lighting conditions within animal rooms are potentially significant and often underappreciated variables within experiments. Disruption of the light/dark cycle, primarily by exposing animals to light at night (LAN), disturbs biological rhythms and has widespread physiological consequences because of mechanisms such as melatonin suppression, sympathetic stimulation, and altered circadian clock gene expression. Thus, attention to the lighting environment of laboratory animals and maintaining consistency of a light/dark cycle is imperative for study reproducibility. Light intensity, as well as wavelength, photoperiod, and timing, are all important variables. Although modern rodent facilities are designed to facilitate appropriate light cycling, there are simple ways to modify rooms to prevent extraneous light exposure during the dark period. Attention to lighting conditions of laboratory animals by both researchers and research care staff ensures best practices for maintaining animal welfare, as well as reproducibility of research results. (PsycINFO Database Record

Chronic exposure to dim artificial light at night decreases fecundity and adult survival in Drosophila melanogaster

The presence of artificial light at night is expanding in geographical range and increasing in intensity to such an extent that species living in urban environments may never experience natural darkness. The negative ecological consequences of artificial night lighting have been identified in several key life history traits across multiple taxa (albeit with a strong vertebrate focus); comparable data for invertebrates is lacking. In this study, we explored the effect of chronic exposure to different night-time lighting intensities on growth, reproduction and survival in Drosophila melanogaster. We reared three generations of flies under identical daytime light conditions (2600lx) and one of four ecologically relevant ALAN treatments (0, 1, 10 or 100lx), then explored variation in oviposition, number of eggs produced, juvenile growth and survival and adult survival. We found that, in the presence of light at night (1, 10 and 100lx treatments), the probability of a female commencing oviposition and the number of eggs laid was significantly reduced. This did not translate into differences at the juvenile phase: juvenile development times and the probability of eclosing as an adult were comparable across all treatments. However, we demonstrate for the first time a direct link between chronic exposure to light at night (greater than 1lx) and adult survival. Our data highlight that ALAN has the capacity to cause dramatic shifts in multiple life history traits at both the individual and population level. Such shifts are likely to be species-specific, however a more in depth understanding of the broad-scale impact of ALAN and the relevant mechanisms driving biological change is urgently required as we move into an increasing brightly lit future.