Hormonal Mechanisms for Parental Control

PI：道格拉斯W. Moc，CO-PI：Hubert G. Schwabl IBN-9604370 近年来，父母平等对待所有子女的普遍假设受到了质疑。 在许多动物和植物群体中，父母产生的同时繁殖的后代数量比通常所能完全支持的要多，迫使家庭规模随后向下调整。 亲本过量生产的根本原因来自多种环境不可预测性来源（包括资源的不可预测性、后代的意外损失、部分幼仔捕食、家庭成员或其他人的同类相食等），但事实上，它同时产生了兄弟姐妹之间的竞争，这就促使父母产生一种等级兄弟姐妹关系，以尽量减少这种竞争的成本。 因此，父母赋予某些后代特殊的优势和/或其他障碍，所谓的边缘育雏成员。 对生物学上的双亲偏爱的研究最多的表现可能是许多掠食性鸟类的异步孵化。 在那里，早期的孵化给了第一个产下的蛋中的胚胎一个发育的领先优势，这有助于它们在任何随后的兄弟姐妹争夺有限食物的竞争中取得成功。 休伯特·施瓦布尔最近发现，雌性实验室金丝雀在产卵过程中会将越来越多的睾丸激素存款到蛋黄中，这表明了父母操纵后代的一种新机制，并激发了从牛背鹭（牛背鹭）收集新鲜鸡蛋的灵感，牛背鹭是一种具有致命的兄弟姐妹攻击（或同胞杀戮）行为的物种。 的 该种第三枚卵的卵黄睾酮（加上两种类似的类固醇）含量远低于其两个巢伴，它们通常提前1-3天孵化。 事实上，白鹭的模式（减少类固醇剂量）是完全相反的，发现在金丝雀，但一致的孵化的影响，表明激素沉积到蛋黄可能是一个广泛的和灵活的父母适应操纵内育雏竞争动态和生存。 拟议的研究旨在通过两项实地研究探讨这一问题。 首先，牛白鹭系统将通过向最后产下的蛋中注射不同水平的3-类固醇鸡尾酒进行实验操作，然后测量在野外条件下孵化的幼鸟随后的竞争行为（乞讨和战斗）。 如果类固醇操纵是进化的父母管理兄弟姐妹竞争的策略的一部分，那么最后一个鸡蛋被提高的育雏应该表现出升级的战斗和乞求，最终损害父母的利益。 第二，为了检验母亲减少类固醇的使用是否是一种普遍现象，是否与同胞竞争特别激烈的家族有关，将对其他同胞竞争物种进行探索性调查，每个物种都与一个密切相关但不具攻击性的姐妹物种配对。 与牛背鹭的试点工作一样，一旦每一个蛋被产下，就将收集一窝蛋，它们的蛋黄被冷冻，以备以后实验室对类固醇含量的分析。 通过这项工作，我们希望增加对自然条件下父母生殖策略的了解，并确定母体类固醇剂量是否是用于增强父母适应度的一般机制。

PI: Douglas W. Moc, CO-PI: Hubert G. Schwabl IBN-9604370 In recent years, the general assumption that parents value all of their offspring equally has come into question. In many animals and plant groups, parents produce greater numbers of concurrent young than can ordinarily be supported fully, forcing a subsequent adjustment downward in family size. The underlying reasons for parental overproduction stem from multiple sources of environmental unpredictability (including resource unpredictability, accidental losses of progeny, partial-brood predation, cannibalism by family members or others, ect.), but the fact of it simultaneously generates sibling rivalry, which creates incentives for parents to produce a hierarchical sibship to minimize the costs of such rivalry. Thus, parents confer special advantages on some offspring and/or handicaps on other, so called marginal brood members. The best-studied manifestation of biological parental favoritism is probably asynchronous hatching in many predatory birds species. There, early onset of incubation gives embryos in the first- laid eggs a developmental head-start that facilitates their success in any ensuing sibling competitions for limited food. Hubert Schwabl s recent discovery that female laboratory canaries deposit increasing amounts of testosterone into yolks as the laying process proceeds suggested a new mechanism for parental manipulation of offspring vigar and inspired the collection of fresh eggs from cattle egrets (Bubulcus ibis), a species known to practice fatal sibling aggression (or siblicide ). The marginal third egg of this species contained much less yolk testosterone (plus two similar steroids) than those of its two nestmates, which normally hatch 1-3 days earlier. The fact that the egret pattern (decreasing steroid dose) is exactly opposite that found in canaries, but congruent with the effects of hatching asynchrony, suggests that hormone depositions into yolks could be a widespread and flexible parental adaptation for rigging intra-brood competitive dynamics and survival. The proposed study aims to explore this matter through two field studies. First, the cattle egret system will be experimentally manipulated by injecting various levels of a 3-steroid cocktail into last-laid eggs, then measuring the subsequent competitive behaviors (begging and fighting) of the hatchlings under field conditions. If steroid-manipulation is part of an evolved parental strategy for managing sibling competition, broods with boosted last- eggs should show escalated fighting and begging, ultimately to the detriment of parental interests. Second, to test whether the mother s cutback on steroids is a general phenomenon and associated with families in which sib- competition is especially keen, an exploratory survey will be made of the other siblicidal species, each paired with a closely-related but nonaggressive sister species. As with cattle egret pilot work, clutches of eggs will be collected as soon as each is laid, their yolks frozen for later laboratory assays of steroid content. Through this work, we expect to increase understanding of the reproductive strategies of parents under natural conditions and to determine whether maternal steroid dosing is a general mechanism used to enhance parental fitness.