Parental effects and the adaptive generation of helpers in a cooperative bird

人们常说，不管我们喜欢与否，总有一天我们会变成我们的父母。对实验动物和人类的研究表明，这不仅是因为我们与父母的基因相似，还因为我们早期的生活经历塑造了我们成年后的外表和行为方式。然而，在这些模式的发展中存在两个主要的不确定性。首先，我们和父母相似仅仅是因为我们生活在同一个环境中吗？其次，父母是否真的通过对我们不同程度的投资来影响我们的发展，如果是这样，这种情况何时发生，对谁有利？为了回答这些问题，我们必须使用一种动物，在这种动物身上，我们可以在自然环境中，在它们发育的不同阶段，道德地移动它们的后代，然后测量它们成年后的行为。我将使用一只50克重的澳大利亚鸟，它像人类一样生活在家庭群体中，在这种群体中，除了父母之外，后代还由不同数量的帮手抚养。在过去的8年里，我一直在研究澳大利亚东南部干旱地区的约90个栗色冠牙巴繁殖群。这个物种非常适合这个项目的目标，因为母亲对后代的投资差异很大，对卵子的投资时间和数量，以及与后代一起抚养的竞争对手的数量和性别都不同。同样，母亲、父亲和帮助者在孵化后为后代提供的食物数量上也有很大差异，有些人几乎不提供食物，而另一些人则提供大部分食物。最后，一个群体的成功取决于它有多少帮助者：后代的存活率会增加，直到群体规模达到8，之后就不会再增加了。因为帮助者几乎都是前些年的后代，所以一小群咿呀学语者应该努力生出帮助者，而一大群则应该努力生出分散者，分散者会离开去组建一个新的咿呀学语者群体。通过在不同大小和不同发育阶段的群体之间移动后代，我将为以下问题提供答案。(1)母亲、父亲和帮助者在多大程度上试图创造乐于助人与自私的后代，他们是否都同意什么时候应该这样做？(2)后代是忽视这种“安排”还是从中受益，还是被他们的教养所操纵，以某种方式行事？(3)如果一只雏鸟的成长环境影响了它们成年后的外表和行为，那么这种影响是什么时候产生的呢？是在雏鸟孵化前受到妈妈的影响，还是在雏鸟在巢中获得食物时受到影响，还是在雏鸟离开巢开始自谋生路后受到影响？这些问题的答案将揭示动物和人类的成长如何塑造我们成年后的外表和行为方式，并有助于回答长期存在的问题：什么是好母亲、好父亲和好帮手？如果从这些结果中，我们能够根据后代的发展预测他们的合作倾向和自私倾向，我们就可以开始指导未来的人类研究，询问儿童发展过程中是否存在一个敏感时期，影响我们成年后的行为。什么时候，什么类型的经历对它最敏感？

It is often said that one day, whether we like it or not, we will turn into one of our parents. Research in both laboratory animals and humans, suggests that this is not only because of our genetic similarities with our parents, but because our early life experiences shape the way we look and behave in adulthood. However, two major uncertainties exist in the development of these patterns. First, do we simply resemble our parents because we share the same environment? Second, do parents actually shape our development through varying their levels of investment in us, and if so, when does this happen and for whose benefit is it? To answer these questions we must use an animal in which we can ethically move offspring around in a natural setting at different stages of their development and then measure their behaviour in adulthood. I will use a 50g Australian bird that lives, like humans, in family groups in which offspring are reared by a variable number of helpers in addition to parents. I have been studying ~90 breeding groups of the chestnut-crowned babbler in the arid zone of south-eastern Australia for the last 8 years. This species is perfect for the aims of this project because mothers vary tremendously in their investment in offspring, varying the timing and amount of investment in eggs, as well as the number and sex of competitors with which offspring will be reared. Similarly, mothers, fathers and helpers vary significantly in how much food they provide to offspring after hatching, with some providing almost nothing and others contributing the majority of it. Finally, the success of a group depends on how many helpers it has: the survival of offspring increases until group size reaches 8, after which there are no further increases. Because helpers are almost always offspring from previous years, a small group of babblers should try to produce helpers, whereas a large group should try to produce dispersers that go off to start a new babbler group. By moving offspring between groups of different sizes and at different stages of their development, I will provide an answer to the following questions. (1) To what degree do mothers, fathers and helpers try to create helpful versus selfish offspring, and do they all agree when this should be? (2) Do offspring ignore this 'arrangement' or benefit from it, or are they being manipulated to behave in a way dictated by their up-bringing? (3) If one's upbringing influences the way they look and behave in adulthood, when is this effect generated, is it by the mum's before hatching, is it when they receive food in the nest, or is it determined after they leave the nest and begin to fend for themselves? The answers to these questions will shed new light on how the upbringing of animals and humans shapes the way we look and behave in adulthood and help answer the long-standing questions of what makes a good mother, father and helper and who is it good for? If, from these results, we are able to predict the cooperative versus selfish tendencies of offspring given their development, we can begin to direct future studies in humans to ask whether there is a sensitive period during child development that shapes our behaviour in adulthood? When is it and what types of experiences is it most sensitive to?