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

Species have been adapted to specific niches optimizing survival and reproduction; however, urbanization by humans has dramatically altered natural habitats. Artificial light at night (LAN), termed ‘light pollution’, is an often overlooked, yet increasing disruptor of habitats, which perturbs physiological processes that rely on precise light information. For example, LAN alters the timing of reproduction and activity in some species, which decreases the odds of successful breeding and increases the threat of predation for these individuals, leading to reduced fitness. LAN also suppresses immune function, an important proxy for survival. To investigate the impact of LAN in a species naive to light pollution in its native habitat, immune function was examined in Siberian hamsters derived from wild-caught stock. After four weeks exposure to dim LAN, immune responses to three different challenges were assessed: (i) delayed-type hypersensitivity (DTH), (ii) lipopolysaccharide-induced fever, and (iii) bactericide activity of blood. LAN suppressed DTH response and reduced bactericide activity of blood after lipopolysaccharide treatment, in addition to altering daily patterns of locomotor activity, suggesting that human encroachment on habitats via night-time lighting may inadvertently compromise immune function and ultimately fitness.

Download Full-text

Exposure to artificial light at night alters innate immune response in wild great tit nestlings

Journal of Experimental Biology ◽

10.1242/jeb.239350 ◽

2021 ◽

Author(s):

Ziegler Ann-Kathrin ◽

Watson Hannah ◽

Hegemann Arne ◽

Meitern Richard ◽

Canoine Virginie ◽

...

Keyword(s):

Nitric Oxide ◽

Immune Response ◽

Immune Function ◽

Innate Immune Response ◽

Great Tit ◽

Innate Immune ◽

Artificial Light ◽

Immune Challenge ◽

Light At Night ◽

Dark Night

The large-scale impact of urbanization on wildlife is rather well documented, however the mechanisms underlying the effects of urban environments on animal physiology and behaviour are still poorly understood. Here, we focused on one major urban pollutant - artificial light at night (ALAN) - and its effects on the capacity to mount an innate immune response in wild great tit Parus major nestlings. Exposure to ALAN alters circadian rhythms of physiological processes, by disrupting the nocturnal production of the hormone melatonin. Nestlings were exposed to a light source emitting 3 lux for seven consecutive nights. Subsequently, nestlings were immune-challenged with a lipopolysaccharide injection, and we measured haptoglobin and nitric oxide levels pre- and post-injection. Both haptoglobin and nitric oxide are important markers for innate immune function. We found that ALAN exposure altered the innate immune response, with ALAN nestlings having lower haptoglobin and higher nitric oxide levels after the immune-challenge compared to dark-night nestlings. Unexpectedly, nitric oxide levels were overall, lower after the immune-challenge than before. These effects were likely mediated by melatonin, since ALAN-treated birds had on average 49% lower melatonin levels than the dark-night birds. ALAN exposure did not have any clear effects on nestling growth. This study provides a potential physiological mechanism underlying the documented differences in immune function between urban and rural birds observed in other studies. Moreover, it gives evidence that ALAN exposure affects nestling physiology, potentially causing long-term effects on physiology and behaviour, which ultimately can affect their fitness.

Download Full-text

Melatonin: a possible link between the presence of artificial light at night and reductions in biological fitness

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2014.0122 ◽

2015 ◽

Vol 370 (1667) ◽

pp. 20140122 ◽

Cited By ~ 39

Author(s):

Therésa M. Jones ◽

Joanna Durrant ◽

Ellie B. Michaelides ◽

Mark P. Green

Keyword(s):

Immune Function ◽

Ecological Impacts ◽

Negative Effects ◽

Light At Night ◽

Model Species ◽

Constant Illumination ◽

Future Studies ◽

Key Driver ◽

Dose Dependent ◽

Positive Effect

The mechanisms underpinning the ecological impacts of the presence of artificial night lighting remain elusive. One suspected underlying cause is that the presence of light at night (LAN) supresses nocturnal production of melatonin, a key driver of biological rhythm and a potent antioxidant with a proposed role in immune function. Here, we briefly review the evidence for melatonin as the link between LAN and changes in behaviour and physiology. We then present preliminary data supporting the potential for melatonin to act as a recovery agent mitigating the negative effects of LAN in an invertebrate. Adult crickets ( Teleogryllus commodus ), exposed to constant illumination, were provided with dietary melatonin (concentrations: 0, 10 or 100 µg ml −1 ) in their drinking water. We then compared survival, lifetime fecundity and, over a 4-week period, immune function (haemocyte concentration, lysozyme-like and phenoloxidase (PO) activity). Melatonin supplementation was able only partially to mitigate the detrimental effects of LAN: it did not improve survival or fecundity or PO activity, but it had a largely dose-dependent positive effect on haemocyte concentration and lysozyme-like activity. We discuss the implications of these relationships, as well as the usefulness of invertebrates as model species for future studies that explore the effects of LAN.

Download Full-text