PHOTOPERIODISM AND SEASONAL BREEDING IN THE TROPICS

已经花费了大量的努力来理解 哺乳动物繁殖的光周期控制。尽管 这一努力，仍然有相当大比例的无知。完毕 四分之三的哺乳动物生活在热带地区，然而 光周期调节仍然只与动物有关 模特来自生活在温带地区的四分之一。 我们不知道哺乳动物是否有能力做出反应 对它们所经历的日长的微小变化进行繁殖 在热带地区。如果他们确实有这种能力，我们不知道他们是否 用它来调节它们的季节性繁殖。如果此容量为 如果没有，我们不知道为什么在遗传和神经内分泌方面 缺席了。目前的提案回答了所有这些问题。 三种小型哺乳动物将被季节性地困在 委内瑞拉恶劣的环境，那里每年有一小时的 白天长度的变化：一种老鼠大小的僵硬的有袋类动物 季节性繁殖者；全年繁殖的啮齿动物；啮齿动物 这在其季节性上是中等的。实验室培育的后代 这些动物中的一部分将挑战为成熟或较短的日长， 无论有没有额外的社会影响力。在适当情况下， 将确定临界日长，并与之进行比较 在精子发生和卵子发生开始和停止时存在 在野外季节性繁殖。因此，我们将了解到这些 动物对光有很强的反应能力，如果有些动物 实际使用这种能力。 被发现对光周期不敏感的物种将被测试 确定它们没有响应的原因。初步实验将 关注他们测量白天长度的方式，他们如何分泌 褪黑素，它们对这种激素的反应，以及是否 日长影响黄体生成素的负反馈灵敏度 性腺类固醇的分泌物。被发现的异质性物种 对光周期的反应将受到实验的影响 旨在(A)看看生殖的光响应性是否可以 通过基因选择在这些动物中重新建立；(B)探索 数量上的异质性的遗传基础；和(C) 确定关注点与神经内分泌的关系 机械装置。 所有这一切的结果将是一套新的原则和动物 更能真实地代表哺乳动物的模型 完整的。

An immense amount of effort has been expended in understanding the photoperiodic control of reproduction in mammals. Despite this effort, an ignorance of great proportion still remains. Over three quarters of all mammals live in the tropics, yet the state of photoperiodic regulation remains tied exclusively to animal models drawn from the one quarter living in the temperate zone. We don't know if mammals have the capacity to react reproductively to the small variation in daylength they experience in the tropics. If they do have this capacity we don't know if they use it to regulate their reproduction seasonally. If this capacity is absent we don't know why in genetic and neuroendocrine terms it is absent. The present proposal speaks to all of these questions. Three species of small mammals will be trapped in a seasonally harsh environment in Venezuela where there is one hour of annual variation in daylength: a mouse-sized marsupial that is a rigid seasonal breeder; a rodent that breeds year around, and a rodent that is intermediate in its seasonality. Laboratory bred offspring of these animals will challenged to mature or short daylengths, both with and without added social influence. Where appropriate, critical daylength will be determined and compared with that existing when spermatogenesis and oogenesis start and stop seasonally in the wild. Thus we will learn whether or not these animals are reproductively photoresponsive and if some of them actually use this capacity. Species found to be unresponsive to photoperiod will be tested to determine why they are not responsive. Initial experiments will focus on the way they measure daylength, how they secrete melatonin, how they react to this hormone, and whether or not daylength influences the negative feedback sensitivity of LH secretion to gonadal steriods. Species found to be heterogenously responsive to photoperiod will be subjected to experiments designed to (a) see if reproductive photoresponsiveness can be reestablished in these animals via genetic selection; (b) explore quantitatively the genetic basis for the heterogeneity; and (c) determine how the loci of concern relate to neuroendocrine mechanisms. The results of all of this will be a new set of principles and animal models that are more truly representative of mammals as a whole.