Organisms use changes in photoperiod for seasonal reproduction to maximize the survival of their offspring. Birds have sophisticated seasonal mechanisms and are therefore excellent models for studying these phenomena. Birds perceive light via deep-brain photoreceptors and long day-induced thyroid-stimulating hormone (TSH, thyrotropin) in the pars tuberalis of the pituitary gland (PT), which cause local thyroid hormone activation within the mediobasal hypothalamus. The local bioactive thyroid hormone controls seasonal gonadotropin-releasing hormone secretion and subsequent gonadotropin secretion. In mammals, the eyes are believed to be the only photoreceptor organ, and nocturnal melatonin secretion triggers an endocrine signal that communicates information about the photoperiod to the PT to regulate TSH. In contrast, in Salmonidae fish the input pathway to the neuroendocrine output pathway appears to be localized in the saccus vasculosus. Thus, comparative analysis is an effective way to uncover the universality and diversity of fundamental traits in various organisms.

中文翻译：

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脊椎动物繁殖的光周期调控。

生物利用光周期的变化来季节性繁殖，以最大限度地提高其后代的生存。鸟类具有复杂的季节机制，因此是研究这些现象的绝佳模型。鸟类通过脑下垂体（PT）结节中的深脑感光器和长日诱导的甲状腺刺激激素（TSH，促甲状腺激素）感知光，这会引起中下丘脑下的局部甲状腺激素活化。局部生物活性甲状腺激素控制季节性促性腺激素释放激素分泌和随后的促性腺激素分泌。在哺乳动物中，眼睛被认为是唯一的感光器官，夜间褪黑激素的分泌会触发内分泌信号，该信号将有关光周期的信息传达给PT以调节TSH。相反，在鲑鱼科鱼类中，通往神经内分泌输出途径的输入途径似乎位于结膜血管中。因此，比较分析是揭示各种生物基本特征的普遍性和多样性的有效方法。