Nicholls T J, Follett B K, Goldsmith A R, Pearson H
Department of Zoology, University of Bristol, United Kingdom.
Reprod Nutr Dev (1980). 1988;28(2B):375-85. doi: 10.1051/rnd:19880304.
Comparisons are drawn between the photoperiodically driven breeding cycles in "long-day" birds and "short-day" mammals, emphasizing the importance of photorefractoriness as a key regulator in the timing processes. It is argued that the two types of breeding cycle may not be so radically different as previously thought and, indeed the cycles may be strictly homologous. Evidence in support of this comes from the role of the thyroid glands in seasonality. In starlings and quail, thyroidectomy prevents refractoriness developing and the birds remain in breeding indefinitely under long days. If the processes underlying refractoriness are similar across species then thyroidectomy should greatly alter the ewe's breeding cycle. In two experiments, Welsh Mountain ewes were thyroidectomized in the summer during anoestrus and their subsequent periods of oestrus monitored under various daylengths. There was no effect of thyroidectomy on the time when oestrous cyclicity began in the Autumn but the onset of anoestrus was profoundly disrupted. All the ewes continued to cycle well beyond the end of the normal breeding season and a number have continued throughout the entire period of anoestrus.
人们对“长日照”鸟类和“短日照”哺乳动物中由光周期驱动的繁殖周期进行了比较，强调了光不应性作为时间进程关键调节因子的重要性。有人认为，这两种繁殖周期可能不像之前认为的那样有根本差异，实际上这些周期可能是严格同源的。支持这一观点的证据来自甲状腺在季节性方面的作用。在椋鸟和鹌鹑中，甲状腺切除可防止不应性的发展，鸟类在长日照条件下可无限期地保持繁殖状态。如果不同物种间不应性的潜在过程相似，那么甲状腺切除应会极大地改变母羊的繁殖周期。在两项实验中，威尔士山地母羊在夏季乏情期进行了甲状腺切除，并在不同日长条件下监测其随后的发情期。甲状腺切除对秋季发情周期开始的时间没有影响，但乏情期的开始受到了严重干扰。所有母羊在正常繁殖季节结束后仍继续发情，并且有一些母羊在整个乏情期都持续发情。
