COLLABORATIVE RESEARCH: Timing of Reproduction: Nutrition-Endocrine Interactions

动物在一年中最可能成功繁殖后代的时间开始繁殖是至关重要的。如果依赖的幼鸟在一个季节过早或过晚出现，父母可能没有足够的食物来喂养它们的后代。哺乳期的雌鸟将可利用的食物资源转化为乳汁喂养幼鸟，与哺乳期的雌鸟不同，大多数雏鸟吃的是昆虫，它们的丰度随季节变化。PIs注意到，在佛罗里达灌木松鸦（Aphelocoma coerulescens）中，生活在郊区栖息地的松鸦比生活在自然环境中的松鸦更早开始繁殖（在阿奇博尔德生物站，ABS），早期繁殖的一个明显结果是郊区幼鸟的状况较差，存活率低于ABS（汽车和宠物等原因的影响已被排除在分析之外）。先前的实验和观察指出，人类提供的食物是郊区早期繁殖的潜在原因。虽然食物已被证明是决定许多物种雌性何时开始繁殖的一个重要因素，但食物中是否含有特定的营养物质，如蛋白质（或构成蛋白质的特定必需氨基酸）、脂肪，或这两者的组合，目前尚不清楚。pi将为ABS的雌性提供高蛋白（包括必需氨基酸）、高脂肪或两者都高的食物补充剂，以确定这些营养线索在繁殖时间的重要性。为了更好地理解营养线索导致雌性松鸦开始繁殖的生理机制，pi将回答以下问题：1)独立于内容的可靠食物来源是否会导致早期繁殖？2)在决定何时开始繁殖时，特定的营养物质是否必不可少？如果是这样，哪种营养物质作为提示，告知雌性何时开始繁殖？3)这些营养物质的血液或全身水平是雌性决定繁殖的关键吗？4)关于女性营养状况的信息是通过激素的方式传达的吗？如果是，涉及到哪些激素？除了确定不同的补充饮食对卵泡起始时间的影响外，pi还将通过测量血浆中生殖激素（黄体生成素、睾酮和雌二醇）和总蛋白的水平来回答上述问题。pi还将测量瘦素水平，这是一种与一些哺乳动物开始繁殖有关的激素：这可能是一种激素暗示，告诉雌性她的状况适合开始繁殖。通过考虑许多生理因素，pi将了解生物体如何将营养信息整合到何时开始繁殖的决定中。本研究将有助于了解资源的可用性如何影响亚热带季节性繁殖动物的行为、生理和健康，特别是受威胁的佛罗里达灌木杰伊。

It is essential that animals initiate their reproductive effort at time of year that maximizes the likelihood of successful production of young. If dependent young are present either too early or late in a season, there may be insufficient food for the parents to feed their offspring. Unlike mammals, in which a lactating female converts available food resources into milk to be fed young, most nestling birds are fed insects whose abundance varies seasonally. The PIs noted that in the Florida Scrub-Jay (Aphelocoma coerulescens), jays that live in a suburban habitat begin breeding earlier than jays living in their natural environment (at Archbold Biological Station, ABS) and that one apparent result of early breeding is that suburban-young are in poorer condition and survivorship is lower that it is at ABS. (Effects from causes such as automobiles and pets have been factored out of the analyses). Previous experiments and observations point toward human-provided food as the underlying cause of early breeding in the suburbs. Although food has been shown to be an important factor in the decision of when to begin breeding in females of many species, whether it is specific nutrients within the food, such as proteins (or specific essential amino acids that are the building-blocks of proteins), fats, or a combination of these two is less clear. The PIs will provide females at ABS with food supplements that are high in protein (including essential amino acids), high in fats, or high in both to determine the import of these nutritional cues upon the timing of reproduction. To better understand the physiological mechanisms by which the nutritional cues lead to the initiation of reproduction in female jays the PIs will answer the following questions: 1) Does the presence of a reliable food source, independent of content, lead to early breeding? 2) Are specific nutrients essential in the decision of when to begin breeding and, if so, which nutrient serves as the cue to inform a female when to begin breeding? 3) Are blood or whole body levels of these nutrients key in the female's decision to breed? 4) Is the information about the female's nutritional state communicated by hormonal means and, if so, what are the hormones involved? In addition to determining the effects of the different supplementary diets upon timing of clutch initiation, the PIs will answer the answer the preceding questions by measuring plasma levels of reproductive hormones (luteinizing hormone, testosterone, and estradiol) and total protein. The PIs will also measure levels of leptin, a hormone that is involved in the onset of reproduction in some mammals: this makes it a possible hormonal cue that informs a female that her condition is suitable to begin reproduction. By considering numerous physiological factors, the PIs will learn how an organism integrates nutritional information into its decision of when to begin reproduction. This research will contribute significantly to the understanding of how resource availability affects the behavior, physiology, and fitness of seasonally breeding animals in the sub-tropics, especially the threatened Florida Scrub-Jay.