Falk H, Gwinner E
Max-Planck-Institut für Verhaltensphysiologie, Vogelwarte, Andechs, Federal Republic of Germany.
Biol Reprod. 1988 Dec;39(5):1004-8. doi: 10.1095/biolreprod39.5.1004.
In European starlings, as in many other birds inhabiting higher latitudes, gonads develop in response to the increasing daylengths in early spring. Later in the year, however, the hypothalamo-pituitary-gonadal axis becomes refractory to the previously stimulatory long photoperiods and the gonads regress in summer. The present study addresses the question of when during the gonadal growth phase photorefractoriness is determined. A 13-h photoperiod induces testicular development and subsequent testicular regression associated with refractoriness in male starlings. An 11-h photoperiod, in contrast, induces only testicular development, and photorefractoriness never develops. When starlings were transferred to an 11-h photoperiod, either 12 or 25 days following exposure to a 13-h photoperiod, their testes developed to full size, but remained large to the end of the experiment, i.e. refractoriness did not develop. The same was even true of most birds in a third group that were transferred to an 11-h photoperiod after 46 days of the 13-h photoperiod, when gonads had developed to near maximal size. These data show that, in contrast to some other species of passerine birds, the onset of photorefractoriness does not become fixed before the testes have undergone considerable development, and that the photoperiodic conditions experienced at the end of the testicular growth phase are still effective in determining the precise time of onset of photorefractoriness. It is suggested that this peculiarity of the starling is related to the fact that its gonadal development begins rather early in spring and, hence, under much shorter photoperiods than the other species studied.
与许多栖息在高纬度地区的其他鸟类一样，欧洲椋鸟的性腺会随着早春白昼时长的增加而发育。然而，在一年中的晚些时候，下丘脑-垂体-性腺轴对先前具有刺激作用的长光照周期变得不应期，性腺在夏季退化。本研究探讨了在性腺生长阶段的何时确定光不应期的问题。13小时的光照周期会诱导雄性椋鸟的睾丸发育以及随后与不应期相关的睾丸退化。相比之下，11小时的光照周期仅诱导睾丸发育，且从不出现光不应期。当椋鸟在暴露于13小时光照周期后的12天或25天被转移到11小时光照周期时，它们的睾丸发育到最大尺寸，但在实验结束时仍保持较大，即未出现不应期。在第三组中，大多数鸟类在13小时光照周期持续46天后被转移到11小时光照周期，此时性腺已发育到接近最大尺寸，情况也是如此。这些数据表明，与其他一些雀形目鸟类不同，光不应期的开始在睾丸经历相当程度的发育之前并不固定，并且在睾丸生长阶段结束时所经历的光周期条件在确定光不应期开始的确切时间方面仍然有效。有人认为，椋鸟的这种特性与以下事实有关：其性腺发育在春季相当早的时候就开始了，因此，所处的光照周期比所研究的其他物种短得多。
