Social environment and indirect genetic effects on life history and behavioural traits in mammals

甚至在达尔文之前，寻找个体在行为和其他特征上差异的原因就已经是进化生物学的中心任务之一。这个问题的答案不仅有助于我们理解为什么个体不同，而且还可以确定将影响从行为、发育到复杂疾病表型的特征表达的环境因素。有了潜在的遗传学知识，人们也许能够在一定程度上预测生物体如何发展并对不断变化的环境条件做出反应。近一个世纪以来，人们已经知道，个体可能会因为他们的基因(由于基因的直接遗传效应)或他们所经历的环境的不同而不同。虽然人们已经认识到和研究了基因和环境条件之间相互作用的重要性，但很少有人认识到这样一个事实，即环境只是部分物理的(如温度、生境等)。事实上，大多数动物，包括人类，都暴露在个体相互作用的社会环境中。在早期发育的最具影响力的时期，大多数哺乳动物的兄弟姐妹和父母都是如此。一个非常重要的见解是，社会环境的影响可能有遗传基础，因为与你互动的个人表达的基因会影响你的特征或性格的表达。这些所谓的间接遗传效应背后的原理在母亲身上很容易看出，但它同样适用于兄弟姐妹。了解表型的差异在多大程度上是由相互作用的个体表达的基因造成的，这对群居动物的大多数特征至关重要，也是拟议中的研究要解决的主题。然而，只有掌握了潜在机制的信息，我们才能真正全面地了解间接遗传效应是如何发挥作用的。例如，如果我们希望解释个体之间在生长或行为特征上的差异，间接遗传分析的结果可能表明，这种测量的很大一部分依赖于兄弟姐妹中表达的基因，这影响了他们对兄弟姐妹的竞争行为，并因此影响了局部个体的表型。这个项目的目的是通过一项分析来揭示间接遗传效应发挥作用的机制，该分析不仅从当前项目中获取数据，还从使用相同模型系统的先前进行的研究中获取数据。这种系统遗传学方法只有在像BXD小鼠系统这样的大型遗传参考板上才可能实现，该系统定义了遗传变异，并在其他研究中得到了广泛应用。从进化的角度来看，间接遗传效应很重要，因为社会环境可以对选择和进化做出反应(因为这是有遗传基础的)。此外，直接和间接遗传效应之间的相互作用可能促进或制约性状进化。因此，关于性状表达如何因选择而改变的模型可能会产生对进化动态和结果的完全不同的预测，这取决于是否考虑了间接遗传效应。显然，正如最近的理论研究所表明的那样，我们有充分的理由认为我们需要考虑间接遗传效应，以促进我们对复杂表型变异原因的理解。

Finding the causes for variation among individuals in behaviours and other traits has been, even before Darwin, one of the central quests in evolutionary biology. Not only will an answer to this question help us understand why individuals differ, but can also identify environmental factors that will affect the expression of traits ranging from behavioural, developmental to complex diseases phenotypes. With knowledge about the underlying genetics, one may be able to predict to some degree how organisms develop and respond to changing environmental conditions. It has been known for almost a century that individuals can differ due to differences in their genes (direct genetic effects due to genotype) or the environment they experience. While the significance of interactions between genotype and environmental conditions has been recognized and investigated, much less appreciated is the fact that the environment is only partly physical (e.g. temperature, habitat etc.). Indeed, most animals, including humans, are exposed to a social environment of interacting individuals. During the most influential period in early development these comprise siblings and parents for most mammals. A very important insight is that effects of the social environment can have a genetic basis in that genes expressed in individuals with whom you interact affect the expression of your traits or characters. The rationale behind these so-called indirect genetic effects is easy to see in the case of mothers but it equally applies to siblings. Understanding how much variation in phenotypes is due to genes expressed in interacting individuals is pivotal to most traits characteristic of socially living animals and is the topic to be addressed by the proposed research. Yet, only with information about the underlying mechanisms do we truly gain a comprehensive picture of how indirect genetic effects work. For example, if we wish to explain variation among individuals in e.g. growth or a behavioural trait, a result of an indirect genetic analysis might show that a significant proportion of this measure is dependent on the genes expressed in siblings, which affects their competitive behaviour towards siblings and, as a consequence, the phenotype in the focal individual. This project aims to unravel the mechanisms by which indirect genetic effects work using an analysis that not only takes data from the current project but also from previously conducted studies using the same model system. This systems-genetics approach is only possible with such a large genetic reference panel as the BXD mouse system, for which genetic variation is defined and which has been extensively used in other studies. From an evolutionary perspective, indirect genetic effects are important because the social environment can respond to selection and evolve (since there is a genetic basis to it). Further, interactions between direct and indirect genetic effects might facilitate or constrain trait evolution. Models about how trait expression changes due to selection may thus yield quite different predictions of evolutionary dynamics and outcomes depending on whether indirect genetic effects are considered or not. Clearly, as recent theoretical research shows, we have good reasons to assume that we need to consider indirect genetic effects to advance our understanding of the causes of variation in complex phenotypes.