Universidad Nacional de Córdoba, Facultad de Ciencias Exactas, Físicas y Naturales, Centro de Zoología Aplicada, Córdoba, Rondeau 798, CP X5000AVP, Argentina.
Universidad Nacional de Córdoba, Facultad de Ciencias Químicas, Departamento de Química Orgánica, Instituto de Investigaciones en Fisicoquímica de Córdoba (INFIQC), Córdoba, Av. Haya de la Torre s/n Ciudad Universitaria, X5000HUA, Argentina.
Zoology (Jena). 2020 Jun;140:125769. doi: 10.1016/j.zool.2020.125769. Epub 2020 Mar 26.
In avian species living at high altitudes and latitudes, reproductive events are largely controlled by photoperiod, with changes being perceived mainly through encephalic photoreceptors located in the hypothalamus. It is known that during long day periods (reproductive periods), the information transmitted by brain photoreceptors triggers the production of thyroid hormones that regulate GnRH secretion, inducing secretion of pituitary gonadotropins. As a result, gonads develop and grow and the production of gonadal sex hormones, testosterone and estradiol increases (classic gonadal cycle). During short day periods (non-reproductive periods) on the other hand, the gonads regress, and plasma gonadal steroid levels are low. By means of this mechanism, birds synchronize their physiology and reproductive behaviors with seasonal changes in the environment. However, it appears that not all avian species comply with this general reproductive pattern. For example, the Eared Dove (Zenaida auriculata), a South American opportunistic breeding columbiform, has been reported to successfully reproduce throughout the year, making it an interesting avian system for studying the endocrine basis of avian reproduction. In view of a clear lack of seasonal variability in testicular weight and size (the classic gonadal regression/recrudescence cycle) in the male Eared Dove, we examined whether their reproductive aseasonality could be the result of being in a continuous state of reproductive preparedness. Our results show that despite the absence of a marked gonadal cycle in terms of gonadal volume, plasma testosterone levels in males were minimal during autumn-winter, reaching maximum values during spring-summer. This indicates that male gonad function is not seasonal in terms of spermatogenesis but that circulating testosterone levels are correlated with photoperiod, demonstrating an exception to the classic model of reproduction in birds.
在生活在高海拔和高纬度地区的鸟类中，生殖活动主要受光周期控制，变化主要通过位于下丘脑的脑内光感受器感知。已知在长日照时期（生殖期），大脑光感受器传递的信息触发甲状腺激素的产生，调节 GnRH 的分泌，诱导垂体促性腺激素的分泌。结果，性腺发育和生长，性腺性激素睾酮和雌二醇的产生增加（经典性腺周期）。另一方面，在短日照时期（非生殖期），性腺退化，血浆性腺类固醇水平降低。通过这种机制，鸟类将其生理和生殖行为与环境的季节性变化同步。然而，似乎并非所有鸟类都符合这种普遍的生殖模式。例如，棕头鸦雀（Zenaida auriculata），一种南美机会主义繁殖的鸠鸽，已被报道可以在全年成功繁殖，因此成为研究鸟类生殖内分泌基础的有趣鸟类系统。鉴于雄性棕头鸦雀的睾丸重量和大小（经典性腺退化/复壮周期）在季节性方面没有明显的变化，我们检查了它们的非季节性生殖是否是由于持续处于生殖准备状态的结果。我们的结果表明，尽管在性腺体积方面没有明显的性腺周期，但雄性的血浆睾酮水平在秋季-冬季最低，在春季-夏季达到最大值。这表明，雄性性腺功能在精子发生方面没有季节性，但循环睾酮水平与光周期相关，这表明鸟类经典生殖模式的一个例外。
