Thyroxine and Seasonality in American Tree Sparrows

小行星9603555 大多数动物的繁殖是季节性的，因此是不连续的。 季节性繁殖是对季节性环境的一种适应，并在环境条件最适合养育幼崽时进行。 该项目探索了在美国树麻雀中开启和关闭季节性繁殖的生理机制，这种物种的繁殖周期（1）由日照的年周期驱动，（2）可以在实验室中简单地通过操纵每日的光暗比率来模拟。 长日照（如春季）诱导性腺生长，几周后，性腺退化和婚后蜕皮。 短日照（如在冬季）恢复对长日照的敏感性，从而一旦日照超过一个临界持续时间，允许性腺重新开始生长。 最近对季节性繁殖的鸟类和哺乳动物的研究表明，从繁殖状态到非繁殖状态的转变依赖于甲状腺。 在美国树麻雀中，甲状腺不仅是这种转变所必需的，而且在季节性中起着更普遍的作用，影响繁殖的开始和蜕皮的开始。 事实上，如前所述，长日照和甲状腺激素相互作用，为雄性树麻雀的季节性繁殖和蜕皮编程。 将“季节性”概念化为一套长日甲状腺激素依赖过程的表达是对生殖内分泌学的一个新贡献。 这项拟议中的研究试图通过严格挑战PI的季节性概念模型来验证它。如果雄性树麻雀实际上是为了季节性繁殖而编程的，并且只有在同时暴露于长日照和甲状腺激素的情况下才蜕皮，那么撤回一种或两种编程刺激。（也就是说，撤回长的日子和/或甲状腺激素）后，他们已经被编程不应该损害以后的表达程序化的反应。 在之前的实验中，PI通过撤回甲状腺激素来测试这一推论。 现在，PI将通过在单独的实验中撤回长日照以及长日照和甲状腺激素来测试它。 为了推广该模型的适用性，PI将在受光刺激的雌性树麻雀上进行测试。 其目的是确定季节性繁殖和蜕皮是否像雄性一样是程序化的和依赖甲状腺的。 拟议的研究还试图确定甲状腺激素，这是有助于编程季节性，并显示其行动是否与基因组模型或非基因组模型一致。 了解季节性繁殖的开启和关闭机制，可以提高人类保护濒危物种（例如动物园）、管理猎物和害虫物种、操纵家养物种以获得经济利益以及最大限度地减少模拟甲状腺激素的环境毒素的影响的能力。 ***

9603555 Wilson Most species of animals breed seasonally, thus discontinuously. Seasonal reproduction is an adaptation to a seasonal environment and is timed to occur when environmental conditions are optimal for raising young. This project explores the physiological mechanisms that turn seasonal breeding on and off in American tree sparrows, a species whose reproductive cycle (1) is driven by the annual cycle in daylength, and (2) can be simulated in the laboratory simply by manipulating the daily ration of light and darkness. Long daylengths (as during spring) induce gonadal growth and, several weeks later, gonadal regression and postnuptial molt. Short daylengths (as during winter) restore sensitivity to long days, thereby permitting gonadal growth to begin anew once daylength exceeds a critical duration. Recent work on seasonally breeding birds and mammals has established that the transition from the breeding state to the nonbreeding state is thyroid dependent. In American tree sparrows, the thyroid is not only required for that transition, but plays an even more pervasive role in seasonality, influencing the initiation of breeding and the onset of molt as well. Indeed, as shown earlier, long days and thyroid hormones interact to program male tree sparrows for seasonal reproduction and molt. Conceptualization of "seasonality" as the expression of a suite of long day--thyroid hormone-dependent processes is a novel contribution to reproductive endocrinology. The proposed research seeks to validate the PI's conceptual model of seasonality by rigorously challenging it. If male tree sparrows are, in fact, programmed for seasonal reproduction and molt only when exposed simultaneously to long days and thyroid hormones, then withdrawing one or both of the programming stimuli (that is, withdrawing long days and/or thyroid hormones) after they have been programmed should not compromise later expression of programmed responses. In previous experiments, the PI tested this corollary by withdrawing thyroid hormones. Now the PI will test it by withdrawing, in separate experiments, long days and both long days and thyroid hormones. In an attempt to generalize the model's applicability, the PI will test it on photostimulated female tree sparrows. The goal is to ascertain whether seasonal reproduction and molt are programmed and thyroid dependent, as in males. The proposed research also seeks to identify the thyroid hormone that is instrumental in programming seasonality, and to show whether its actions are consistent with a genomic model or with a nongenomic model. Understanding the mechanisms that turn seasonal reproduction on and off may enhance humankind's ability to preserve endangered species (for example, in zoos), manage game and pest species, manipulate domestic species for economic gain, and minimize the effects of environmental toxins that mimic thyroid hormones. ***