The effects of artificial light at night on Eurasian tree sparrow (Passer montanus): Behavioral rhythm disruption, melatonin suppression and intestinal microbiota alterations

Artificial light at night (ALAN) or light pollution is rapidly widespread with fast urbanization and becomes an obvious environmental disturbance. Recent studies showed ALAN has multiple negative impacts on a wide range of species including bird biological rhythm disruption, behavioral and physiological disturbance and hormone secretion disorder. However, its effects on bird gut microbiota are scarcely studied. In this study, we used Eurasian tree sparrow (Passer montanus), a widely distributed and locally abundant bird species in both urban and rural areas of China to examine the effects of ALAN on locomotor activity rhythm and melatonin secretion, and species diversity and community structure of intestinal microbiota by simulating urban and rural night light environment. Our results showed ALAN strongly affected circadian rhythm of locomotor activity with earlier start of activity before light-on and later rest after light-off. Moreover, ALAN significantly suppressed melatonin release. Last but not least, ALAN profoundly affected taxonomic compositions, species diversity and community structure of intestinal microbiota of birds. We concluded that ALAN may cause bird health damage by disrupting circadian rhythm, inhibiting melatonin release and altering intestinal microbiota. Melatonin hormone level and intestinal microbiota diversity may be important bioindicators for light pollution.