Intensity dependent disruptive effects of light at night on activation of the HPG axis of tree sparrows (Passer montanus)

Apr 11, 2019Environmental pollution (Barking, Essex : 1987)

Stronger light at night more strongly disrupts reproductive hormone activation in tree sparrows

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Abstract

Exposure to 85 lux artificial light at night accelerates reproductive endocrine activation in wild tree sparrows.

Birds exposed to 85 lux light at night showed significantly higher expression of reproductive endocrine genes compared to those at 0 lux.
Higher peak plasma LH and estradiol concentrations were observed in birds exposed to 85 lux, with peaks reached earlier than other groups.
In contrast, birds exposed to 150 and 300 lux light exhibited lower gene expression and peak LH and estradiol values.
The timing of reproductive hormone peaks was not delayed in birds exposed to higher light intensities compared to the control group.
Low intensity artificial light at night is associated with accelerated activation of the reproductive endocrine process, while high intensity is linked to a reduction in this activation.

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Artificial light at night (ALAN) has become increasingly recognized as a disruptor of the reproductive endocrine process and behavior of wild birds. However, there is no evidence that ALAN directly disrupt the hypothalamus-pituitary-gonadal (HPG) axis, and no information on the effects of different ALAN intensities on birds. We experimentally tested whether ALAN affects reproductive endocrine activation in the HPG axis of birds, and whether this effect is related to the intensity of ALAN, in wild tree sparrows (Passer montanus). Forty-eight adult female birds were randomly assigned to four groups. They were first exposed to a short light photoperiod (8 h light and 16 h dark per day) for 20 days, then exposed to a long light photoperiod (16 h light and 8 h dark per day) to initiate the reproductive endocrine process. During these two kinds of photoperiod treatments, the four groups of birds were exposed to 0, 85, 150, and 300 lux light in the dark phase (night) respectively. The expression of the reproductive endocrine activation related TSH-β, Dio2 and GnRH-I gene was significantly higher in birds exposed to 85 lux light at night, and significantly lower in birds exposed to 150 and 300 lux, relative to the 0 lux control. The birds exposed to 85 lux had higher peak values of plasma LH and estradiol concentration and reached the peak earlier than birds exposed to 0, 150, or 300 lux did. The lower gene expression of birds exposed to 150 and 300 lux reduced their peak LH and estradiol values, but did not delay the timing of these peaks compared to the control group. These results reveal that low intensity ALAN accelerates the activation of the reproductive endocrine process in the HPG axis, whereas high intensity ALAN retards it.

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Intensity dependent disruptive effects of light at night on activation of the HPG axis of tree sparrows (Passer montanus)

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