Whitfield-Rucker M, Cassone V M
Department of Biology, Texas A&M University, College Station, Texas, 77843, USA.
Gen Comp Endocrinol. 2000 Apr;118(1):173-83. doi: 10.1006/gcen.2000.7455.
The primary and secondary sexual characteristics of many species of passerine birds undergo dramatic seasonal variation in response to the change in the length of photoperiod. Among the many physiological processes that undergo seasonal changes, bird song and the song control system underlying it undergo similar seasonal variation in size and function. The mechanisms of this seasonal variation are largely unknown but are at least partially due to steroidal action from the gonads. The present study determined the relative roles played by the gonads and the photoperiodic timing system that controls gonadal development on song control nuclei in the brain of the male house sparrow, Passer domesticus. Sparrows maintained in short photoperiods (SD) possessed small regressed testes. Transfer to long photoperiods (LD) for 6 weeks evoked a dramatic increase in testes size, but, after 20 weeks under the same conditions (LDLD), testes completely collapsed. Song control nuclei HVC and RA were smaller in SD than in LD but regressed only moderately in LDLD. Castration of sparrows in SD reduced the amplitude of the seasonal variation but did not completely abolish it. The data support the view that the song control system of the house sparrow is regulated by the photoperiodic timing system independently of gonadal influence, but that the gonads augment seasonal regulation of song, presumably via steroidal hormone secretion.
许多雀形目鸟类的第一性征和第二性征会随着光周期长度的变化而发生显著的季节性变化。在众多经历季节性变化的生理过程中，鸟鸣及其潜在的发声控制系统在大小和功能上也经历类似的季节性变化。这种季节性变化的机制在很大程度上尚不清楚，但至少部分是由于性腺的甾体作用。本研究确定了性腺和控制性腺发育的光周期计时系统在雄性家麻雀（Passer domesticus）大脑中对发声控制核所起的相对作用。处于短光周期（SD）的麻雀睾丸小且萎缩。转移到长光周期（LD）6周会使睾丸大小急剧增加，但在相同条件下（LDLD）20周后，睾丸完全萎缩。发声控制核HVC和RA在SD中比在LD中小，但在LDLD中仅适度萎缩。在SD中对麻雀进行阉割会降低季节性变化的幅度，但并未完全消除。数据支持这样的观点，即家麻雀的发声控制系统受光周期计时系统调节，独立于性腺影响，但性腺可能通过甾体激素分泌增强对鸣叫的季节性调节。
