Effects of day length and temperature on gonadal development, body mass, and fat depots in white-crowned sparrows, Zonotrichia leucophrys pugetensis.
Effects of day length and temperature on gonadal development, body mass, and fat depots in white-crowned sparrows, Zonotrichia leucophrys pugetensis.
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日长和温度对白冠麻雀 Zonotrichia leucophrys pugetensis 性腺发育、体重和脂肪库的影响。
DOI：
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发表时间：
1997
影响因子：
2.7
通讯作者：
S. Schoech
中科院分区：
文献类型：
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作者：
J. Wingfield;J. Wingfield;T. Hahn;T. Hahn;M. Wada;M. Wada;S. Schoech;S. Schoech
我们测试了环境温度（5度，20度和30度）对雄性和雌性白冠麻雀（Zonotrichia leucophrys pugetensis）光周期诱导生殖功能的影响。从短日（9 L-15 D）到长日（16 L-8D）的转移导致在所有三个温度处理中睾丸快速生长和卵巢部分发育。在不同温度下长日暴露30或70天后，睾丸和泄殖腔突起的大小没有差异。然而，与5度和20度组相比，30度组雌性的育雏斑和卵泡发育增强。许多暴露于30 ℃的雌性动物在第70天出现大的卵黄卵泡。然而，只有当雌性动物与雄性动物关在同一个房间时，这种增强才是明显的。尽管高温对卵巢发育有影响，但各组间促卵泡激素或促黄体激素的血浆水平无差异，表明卵巢发育差异可能是由性腺对促性腺激素的敏感性介导的，而不是由这些激素的差异分泌。我们检查了循环水平的皮质酮（B）和三碘甲状腺原氨酸（T3）和甲状腺素（T4）作为可能的调节剂，这种差异卵巢敏感性促性腺激素。血浆B水平在5度和20度时在雄性中显示短暂升高，但在30度时在雄性中受到抑制。B滴度不受雌性动物温度处理的影响。两种性别动物在光刺激后循环T4增加，但在5 ℃时这种增加减少。血浆中的T3浓度变化很大，雄性动物不受光周期或温度的影响，但在第70天暴露于30 ℃的雌性动物中显著较低。因此，B和T4水平似乎不能帮助解释卵巢发育的差异，但循环T3水平不能被排除作为卵巢对促性腺激素敏感性的调节因子。长日照导致雄性和雌性的体重和脂肪存款没有变化或逐渐减少，温度制度对育肥或体重没有进一步的影响。因此，在长日照下的生殖发育似乎对雄性Z.l.的自然相关极端温度具有抗性。pugetensis，而卵泡发育（即，卵黄在卵泡中的沉积导致排卵和筑巢的开始）可以通过高温来增强。这种反应中的二型性的原因尚不清楚，但可以解释为女性在决定最终卵巢成熟和筑巢的开始与有利的环境条件有关。在第二个实验中，性别是相互隔离的，我们确定了同样的处理对Z.I.的影响。pugetensis。同样，温度对光周期诱导的睾丸生长没有影响，在30度下，雌性卵泡发育的增强在没有雄性的情况下大大减少。我们还继续这项实验长达116天的治疗，以研究对光照不应性（自发性腺退化）和基础前换羽发作的影响。在两性中，很明显，低温（5度）延迟性腺退化和高温（30度）提前它。同样，在两性中，在30度和5度的基础前蜕皮分数较大。在给药第116天，温度对LH的血浆水平无影响，但在第116天采样的雄性和雌性动物的5 ℃组中，T4的血浆水平较高。显然，温度的影响对性腺复发、繁殖开始（卵黄沉积）和繁殖终止有不同的影响。在繁殖周期的不同阶段，温度对繁殖功能的影响是否有不同的机制还有待确定。
We tested the effects of ambient temperature (5 degrees, 20 degrees, and 30 degrees) on photoperiodically induced reproductive functions in male and female white-crowned sparrows, Zonotrichia leucophrys pugetensis. Transfer from short days (9L 15D) to long days (16L 8D) resulted in rapid testicular growth and partial ovarian development in all three temperature treatments. There were no differences in sizes of testes and cloacal protuberance following 30 or 70 days of exposure to long days at the different temperatures. However, brood patch and follicular development were enhanced in females at 30 degrees compared with the 5 degrees and 20 degrees groups. Many of these females exposed to 30 degrees had large yolky follicles by Day 70. This enhancement was evident only when females were housed in the same room with males, however. Despite the effects of high temperature on ovarian development, there were no differences among groups in plasma levels of follicle-stimulating hormone or luteinizing hormone, suggesting that differential ovarian development may have been mediated by gonadal sensitivity to gonadotropins rather than by differential secretion of these hormones. We examined circulating levels of corticosterone (B) and both tri-iodothyronine (T3) and thyroxine (T4) as possible regulators of this differential ovarian sensitivity to gonadotropins. Plasma B levels showed transitory increases in males at 5 degrees and 20 degrees, but were suppressed in males at 30 degrees. Titers of B were not influenced by temperature treatments in females. Circulating T4 increased following photostimulation in both sexes, but this increase was reduced at 5 degrees. T3 concentrations in plasma were highly variable and not influenced by either photo-period or temperature in males, but were significantly lower in females exposed to 30 degrees by Day 70. Thus, B and T4 levels do not appear to help explain differential ovarian development, but circulating T3 levels cannot yet be excluded as a regulator of ovarian sensitivity to gonadotropins. Long days resulted in no change, or a gradual decrease, in body mass and fat deposit in males and females, and temperature regimes had no further effects on fattening or body mass. Thus, reproductive development under long days appears to be resistant to naturally relevant temperature extremes in male Z.l. pugetensis, whereas follicular development (i.e., yolk deposition in follicles leading to ovulation and onset of nesting) can be enhanced by high temperature. Reasons for the dimorphism in this response are unknown, but may be explained by the role of females in determining onset of final ovarian maturation and nesting in relation to favorable environmental conditions. In a second experiment, in which the sexes were isolated from one another, we determined the effects of the same treatments on.Z.I. pugetensis. Again there was no effect of temperature on photoperiodically induced testicular growth, and the enhancement of follicular development in females at 30 degrees was greatly reduced in the absence of males. We also continued this experiment up to 116 days of treatment to investigate effects on onset of photorefractoriness (spontaneous gonadal regression) and onset of prebasic moult. In both sexes it was clear that low temperature (5 degrees) retarded gonadal regression and high temperature (30 degrees) advanced it. Similarly, the prebasic moult score was greater at 30 degrees and less at 5 degrees in both sexes. There were no effects of temperature on plasma levels of LH at Day 116 of treatment, but plasma levels of T4 were higher in the 5 degrees group of both males and females sampled at Day 116. Clearly, the effects of temperature can have different effects on gonadal recrudescence, onset of breeding (yolk deposition), and termination of breeding. Whether these influences of temperature on reproductive function at different stages in the breeding cycle have different mechanisms remains to be determ