Schoech Stephan J, Bowman Reed, Hahn Thomas P, Goymann Wolfgang, Schwabl Ingrid, Bridge Eli S
Department of Biological Sciences, University of Memphis, Memphis, Tennessee.
J Exp Zool A Ecol Genet Physiol. 2013 Nov;319(9):527-38. doi: 10.1002/jez.1816. Epub 2013 Aug 22.
Florida scrub-jays (Aphelocoma coerulescens) in the suburbs breed earlier than jays in native habitat. Amongst the possible factors that influence this advance (e.g., food availability, microclimate, predator regime, etc.), is exposure to artificial lights at night (LAN). LAN could stimulate the reproductive axis of the suburban jays. Alternatively, LAN could inhibit pineal melatonin (MEL), thus removing its inhibitory influence on the reproductive axis. Because Florida scrub-jays are a threatened species, we used western scrub-jays (Aphelocoma californica) to investigate the effects of LAN upon reproductive hormones and melatonin. Jays were held under conditions in which the dark-phase of the light:dark cycle was without illumination and then under low levels of LAN. Under both conditions, birds were exposed first to short-days (9.5L:14.5D) that were gradually increased to long-days (14.5L:9.5D). At various times, blood samples were collected during the light part of the cycle to measure reproductive hormones (luteinizing hormone, LH; testosterone, T; and estradiol, E2 ). Similarly, samples to assess melatonin were collected during the dark. In males, LAN caused a depression in LH levels and levels were ∼4× greater under long- than short-days. In females, there was no effect of LAN or photoperiod upon LH. LAN resulted in depressed T levels in females, although there was no effect on T in males. E2 levels in both sexes were lower under LAN than under an unlighted dark-phase. Paradoxically, MEL was higher in jays under LAN, and under long-days. MEL did not differ by sex. LAN disrupted the extraordinarily strong correlation between T and E2 that existed under unlighted nocturnal conditions. Overall, our findings fail to support the hypothesis that LAN stimulates the reproductive axis. Rather, the data demonstrate that LAN tends to inhibit reproductive hormone secretion, although not in a consistent fashion between the sexes.
佛罗里达灌丛鸦（Aphelocoma coerulescens）在郊区的繁殖时间比其在原生栖息地的同类更早。在可能影响这种提前繁殖的诸多因素中（例如食物可获得性、小气候、捕食者情况等），夜间人工光照（LAN）是其中之一。LAN可能会刺激郊区灌丛鸦的生殖轴。或者，LAN可能会抑制松果体褪黑素（MEL），从而消除其对生殖轴的抑制作用。由于佛罗里达灌丛鸦是濒危物种，我们使用西部灌丛鸦（Aphelocoma californica）来研究LAN对生殖激素和褪黑素的影响。将灌丛鸦置于光照：黑暗周期的黑暗阶段无光照的条件下，然后再置于低水平的LAN环境中。在这两种条件下，鸟类首先暴露于短日照（9.5小时光照：14.5小时黑暗），然后逐渐增加到长日照（14.5小时光照：9.5小时黑暗）。在周期的光照时段的不同时间采集血样，以测量生殖激素（促黄体生成素，LH；睾酮，T；和雌二醇，E2）。同样，在黑暗时段采集样本以评估褪黑素。在雄性中，LAN导致LH水平降低，长日照下的水平比短日照下高约4倍。在雌性中，LAN或光周期对LH没有影响。LAN导致雌性T水平降低，尽管对雄性T没有影响。两种性别的E2水平在LAN环境下均低于无光照的黑暗阶段。矛盾的是，在LAN环境下以及长日照条件下，灌丛鸦体内的MEL水平更高。MEL在性别上没有差异。LAN破坏了在无光照夜间条件下T和E2之间存在的极强相关性。总体而言，我们的研究结果不支持LAN刺激生殖轴的假设。相反，数据表明LAN倾向于抑制生殖激素分泌，尽管在两性之间的抑制方式并不一致。
