Hormonal Mechanisms for Parental Control

家长控制的荷尔蒙机制

• 批准号: 9604370
• 负责人: Douglas Mock
• 金额: $ 10.27万
• 依托单位: University of Oklahoma Norman Campus
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1997
• 资助国家: 美国
• 起止时间: 1997-04-01 至 2002-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9604370&HistoricalAwards=false
• 关键词: Hormonal; Mechanisms; Parental; Control

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.

PI：Douglas W. Moc，CO-PI：Hubert G. Schwabl IBN-9604370 近年来，父母平等重视所有后代的普遍假设受到了质疑。 在许多动植物群体中，父母同时产生的后代数量超出了通常能够完全供养的数量，从而迫使家庭规模随后进行调整。 父母过度生产的根本原因源于环境不可预测性的多种原因（包括资源不可预测性、后代的意外损失、部分巢穴捕食、家庭成员或其他人的同类相食等），但这一事实同时产生了兄弟姐妹之间的竞争，从而激励父母产生等级同胞关系，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/或赋予其他所谓的边缘群体成员特殊的优势。 生物亲本偏爱的最充分研究的表现可能是许多掠食性鸟类的异步孵化。 在那里，孵化的早期开始为第一批产下的鸡蛋中的胚胎提供了一个发育的先机，有利于它们在随后的兄弟姐妹竞争中获得有限的食物。 休伯特·施瓦布尔 (Hubert Schwabl) 最近发现，随着产蛋过程的进行，雌性实验室金丝雀在蛋黄中沉积越来越多的睾酮，这表明了父母操纵后代活力的新机制，并启发了从牛背鹭 (Bubulcus ibis) 中收集新鲜卵子，牛背鹭是一种已知会进行致命的兄弟姐妹攻击（或杀兄弟）的物种。 该物种的边缘第三个蛋所含的卵黄睾酮（加上两种类似的类固醇）比其两个巢蛋要少得多，通常会提前孵化 1-3 天。 事实上，白鹭的模式（减少类固醇剂量）与金丝雀中发现的模式完全相反，但与孵化异步的影响一致，这表明激素沉积到蛋黄中可能是一种广泛而灵活的亲本适应，用于操纵巢内竞争动态和生存。 拟议的研究旨在通过两项实地研究来探讨这个问题。 首先，将通过向最后产下的蛋中注射不同浓度的 3-类固醇混合物来对牛背鹭系统进行实验操作，然后测量幼体在野外条件下随后的竞争行为（乞讨和战斗）。 如果类固醇操纵是父母管理兄弟姐妹竞争的进化策略的一部分，那么最后一批蛋数量增加的孩子应该表现出不断升级的争斗和乞讨，最终损害父母的利益。 其次，为了测试母亲减少使用类固醇是否是一种普遍现象，并且与兄弟姐妹竞争特别激烈的家庭有关，将对其他有兄弟姐妹的物种进行探索性调查，每个物种都与一个密切相关但不具有攻击性的姐妹物种配对。 与牛背鹭试点工作一样，一旦产下一窝蛋，我们就会立即收集它们，将蛋黄冷冻起来，以便以后在实验室进行类固醇含量测定。 通过这项工作，我们希望加深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增强父母健康的通用机制。