Costs and consequences of the structured family

早期生活经历的环境可能对成年后的健康和健身产生深远的影响。在提供父母照顾的物种中，依赖父母的幼仔经常一起育雏。因此，密切的关系为增长和发展提供了社会环境。然而，父母的照顾是昂贵的，父母往往最初“过度生产”的数量的后代，他们可以，或愿意，后方。因此，后代的需求可能往往超过父母的资源供应，如食物，这是必要的成长和发展的年轻人。这就为家庭成员之间在父母投资的供应方面产生利益冲突创造了条件。父母提供的资源数量最终取决于环境中资源的可用性。在许多鸟类中，繁殖期间的资源可用性往往是不可预测的，父母可能无法完全控制后代之间的食物分配。然而，父母可以同时跟踪环境中的资源，并通过母体效应增加对育雏内食物分配的控制。不同步孵化，作为早期开始孵化的结果，是一个这样的母亲的影响，导致不同种姓的后代的创建。第一次孵化的“核心”小鸡享有实质性的健身优势，最后孵化的“边缘”小鸡。核心育雏在很大程度上缓冲了环境和发展的不确定性的边缘小鸡，这样的发展和健身的核心小鸡在很大程度上是独立的边缘小鸡的数量在一个育雏。与此相反，边缘后代的健身前景强烈依赖于核心育雏大小和环境条件。通过一些后代的表型障碍来创建这样一个“结构化家庭”，确保父母可以更容易地定制育雏大小以匹配当前条件，并为核心育雏的失败提供保险。然而，很少有人知道边缘后代利用的机制，以克服所施加的障碍，孵化的孵化条件改善（例如，如果一个核心小鸡死亡）。特别是，没有审查现有粮食质量的作用。增加膳食抗氧化剂的可用性，例如类胡萝卜素和维生素E，已被证明可以促进生长，降低对病原体的易感性，并增加雏鸡承受氧化应激的能力。有证据表明，如果早期发展期间经历的恶劣条件随后得到改善，自然选择应该有利于补偿性资源分配和增长。然而，生长补偿并非没有成本，最近已经表明，与快速生长相关的氧化应激的成本可以通过足够的抗氧化剂来降低。因此，提供抗氧化剂可能是一个重要的决定因素的能力，边缘小鸡，以应对食物供应的变化，并弥补在生活中的一个贫穷的开始。与成年人性别有关的不同选择压力也会使雄性和雌性对食物供应的变化作出不同的补偿反应。然而，以前没有考虑过食物质量对结构化家庭的成本和后果的重要性。该项目将量化补偿性资源分配的影响与性别和家庭结构，并通过操纵抗氧化剂的可用性和随后测量的氧化应激在红翅乌鸫（Agelaius phoeniceus）的增长的成本基础进行研究。通过关注边缘小鸡，以及它们通过补偿性资源分配来应对（社会）环境变化的能力，这项工作将突出关键的选择压力，并将评估对环境条件变化的反应的可塑性。

The environment experienced during early life can have profound effects on health and fitness as adults. In species that provide parental care dependent young are often reared together in broods. Close relations consequently provide the social environment in which growth and development takes place. However, parental care is costly and parents often initially 'overproduce' the amount of offspring they can, or are willing to, rear. Consequently offspring demand may often exceed parental supply of resources, such as food, which are necessary for growth and development of young. This creates the conditions for conflicts of interest over the supply of parental investment amongst family members. The amount of resources provided by parents is ultimately dependent upon the availability of resources in the environment. In many birds resource availability during breeding is often unpredictable, and parents may not have full control over the distribution of food among offspring. However, parents can simultaneously track resources in the environment and increase control over within-brood food allocation via maternal effects. Asynchronous hatching, as a consequence of early onset of incubation, is one such maternal effect that leads to the creation of different castes of progeny. First hatched 'core' chicks enjoy substantial fitness advantages over last hatched 'marginal' chicks. Core brood chicks are largely buffered from environmental and developmental uncertainty by marginal chicks, such that the development and fitness of core chicks is largely independent of the number of marginal chicks within a brood. In contrast the fitness prospects of marginal offspring are strongly dependent upon both the core brood size and environmental conditions. The creation of such a 'structured family' through phenotypic handicapping of some offspring ensures parents can more easily tailor brood size to match current conditions and provides insurance against failure of core brood chicks. However, very little is known about the mechanisms utilised by marginal offspring to overcome the handicaps imposed by hatching asynchrony should conditions improve (for example if a core chick dies). In particular, the role of the quality of food available has not been examined. Increased availability of dietary antioxidants for example, such as carotenoids and vitamin E, have been shown to enhance growth, reduce susceptibility to pathogens and increase the ability of chicks to withstand oxidative stress. Evidence suggests that natural selection should favour compensatory resource allocation and growth if poor conditions experienced during early development subsequently improve. However, growth compensation is not free from costs, and it has recently been shown that costs of oxidative stress associated with rapid growth can be reduced by sufficient availability of antioxidants. Consequently the provision of antioxidants may be an important determinant of the ability of marginal chicks to respond to a change in food availability and compensate for a poor start in life. Different selection pressures in relation to sex as adults can also impose differential compensatory responses on males and females to a change in food availability. However, the importance of the quality of food available on the costs and consequences of the structured family has not previously been considered. This project will quantify the effects of compensatory resource allocation in relation to sex and family structure, and examine the cost basis of growth through the manipulation of antioxidant availability and subsequent measurement of oxidative stress in red-winged blackbirds (Agelaius phoeniceus). By focusing on marginal chicks, and their ability to respond to changes in their (social) environment through compensatory resource allocation this work will highlight key selection pressures and will assess plasticity of responses to changes in environmental conditions.