| 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,hormone secretion disorder and immune function decrease.However,the systematic research of its effects on bird circadian rhythm disruption,melatonin suppression,oxidative stress and intestinal microbiota alterations are scarcely studied.In this study,we used Eurasian tree sparrow(Passer montamus),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,melatonin secretion and melatonin receptors(Mel-1a(Melatonin Receptor Type A),Mel-1b(Melatonin Receptor Type B),Mel-1c(Melatonin Receptor Type C))mRNA expressions,corticosterone secretion and corticosterone receptors(GR(Glucocorticoid Receptor),MR(Mineralocorticoid Receptor))mRNA expressions,especially the effects on oxidative stress biomarker levels including total antioxidant capacity(T-AOC),malondialdelyde(MDA),glutathione peroxidase(GPX),superoxide distutase(SOD)and catalase(CAT),and species diversity and community structure of intestinal microbiota by simulating urban and rural night light environment.Our results showed:(1)There is a significant difference between urban and rural lighting intensity.18 sampling points were measured by JAZ 200 spectrometer.The results were 8±0.53 lux for urban night light environment and 0 lux for rural night light.(2)ALAN strongly affected circadian rhythm of locomotor activity.Using Big Brother's automatic activity frequency,the experimental group and the control group tree sparrows were automatically monitored,locomotor activities from both experimental birds and control birds are rhythmic.However experimental birds had ahigher total locomotor activity than control birds.Experimental tree sparrows had earlier and more irequent activity in the morning than the control group tree sparrows.Birds in light pollution group started their activity about an hour before hght-on,and stayed active for about half an hour after light-off,while birds in conlrol group started their activity after light-on and stayed calm after light-off.Tree sparrows in the control group experienced a slow decline from peak to nocturnal activity,while tree sparrows exposed to ALAN.show a sharp decrease in behavior between 10:00 and 14:00.Experimental tree sparrows have more duration than the control group during the entire day's locomotor activity,and the peak value reached is higher than that of the control group.(3)ALAN not only suppressed melatonin secretion,but also disturbed the thythm of melatonin.Melatonin concentration in birds of control group is 2-4 times higher than that in birds of light pollution group.Moreover,control birds exhibited a clear melatonin thythm and melatonin peaked at midnight(0:00)and was reduced significantly in the moming(6:00)and then kept in significantly low level in the daylight(12:00 and 18:00).While.Moreover,melatonin concentration kept low in both daylight and night and lost its circadian pattem in birds of light pollution group.In addition,Expression of Mel-1a and Mel-1b was also inhibited by ALAN and melatonin receptor type C was promoted by ALAN.Moreover,ALAN also disrupted the thythm of melatonin receptors.(4)ALAN inhibited the sccretion of corticosterone.Corticostcrone secretion thythm showed increase daytime(12:00 and 18:00)secretion and decreased nocturnal(0:00 and 6:00)secretion.The concentration of corticosterone in the control group was 1 to 2 times higher than that in the experimental group.The circadian thythm pattern of corticosterone also kept in very low level in the whole day and showed an absence of circadian thythm in experimental birds of light pollution group.ALAN promoted corticosterone receptor GR mRNA level in the liver,but GR,MR in the brain,and MR in the liver expressed differently at different points in every time in experimental birds of light pollution group.(5)Furthermore,ALAN not only affected the activity of three antioxidant enzymes and level of both T-AOC and MDA.but also affected thcir thythm.A significant increase in T-AOC.MDA and SOD activity and an significant dccrcase in GPX and CAT activities were found in the birds under the influences of ALAN compared to the control group.(6)Furthcrmorc.ALAN profoundly affected taxonomic compositions.specics diversity and community structure of intestinal microbiota of sparrows.Lower species diversity and species richness was found in bird of light pollution group suggested light pollution may cause the heavy loss of spccies.The scqucncing depth among all of the samples was calculated using Chaol,ACE richness,Simpson index and Shannon diversity index analyzed by the alpha diversity metric.The average Chaol diversity,ACE richness,Shannon diversity and were Simpson index significantly higher in control group than in the experimental treatments.The beta-diversity analysis was measured to quantify the impact ALAN on gut microbial structure.Based on PCA analysis,the microbial communities of intestinal samples from control and light pollution group were divided into two clear groyps.In addition,hierarchical clustering tree showed that OTUs from birds of control group clustered together into one group by similarity and OTUs from birds of light pollution group gathered into another group,which illustrated that control birds and experimental birds are different in taxonomic compositions of intestinal microbiota.The tree sparrows of control group and light pollution group,Proteobacteria,Firmicutes,and Bacteroides belonged to the dominant flora,and their proportions in the two groups were significantly different,showing different functions.We concluded that ALAN may cause bird health damage by disrupting circadian rhythm,inhibiting melatonin and corticosterone release and their receptors expression and altering oxidative stress levels and intestinal microbiota. |
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