Genetic architecture and constraint in social evolution

尽管达尔文的“适者生存”思想是我们理解地球上生命多样性的核心，但合作行为的进化和维持仍然是一个难题。这是因为，当合作的个体为了互相帮助而做出某种代价高昂的行为时，他们面临着破坏性的作弊者的风险，而这些作弊者没有支付他们公平分担的成本。换句话说，如果作弊是一种更好的策略，那么在人群中如何维持合作行为？为了更好地理解这个问题，我们认为，重要的是首先要确定控制合作行为的基因和途径的性质。这是因为，尽管进化论可能提出了最好的策略，但所需的基因变化可能是不可能的。例如，一些策略可能不存在，因为任何收益都可能被其他健身成本所抵消。或者，它们控制行为的基因和途径的组织方式可能根本不可能由进化来塑造它们实现最佳或有利的策略。在这笔赠款中，我们建议使用一种研究合作行为的简单系统--土壤栖息的社会盘状阿米巴变形虫--来解决这些问题。在有利的条件下，盘阿米巴变形虫以单细胞个体的形式存在，通过摄食细菌进行生长和分裂。然而，饥饿后，多达100,000个阿米巴聚集在一起，共同形成一个多细胞子实体，由死亡的茎细胞支撑的耐寒孢子组成。因此，茎细胞牺牲自己来帮助孢子的传播，这就提出了一个问题，为什么选择不会导致那些没有支付秸秆生产成本公平份额的个人肆无忌惮地作弊。为了实现这一目标，我们将在圆盘藻中采用一种新的方法组合，允许以强大的力量分析合作行为。我们最近发现，即使在少数不同的盘状芽孢杆菌菌株中，也可以检测到不同的社会策略。这项提案中描述的工作将使我们能够在更大的一组菌株中定义和分类策略的数量，因为这可以用来确定进化允许修改社会策略的不同“方式”的数量。然后，我们将通过寻找具有改变的社会行为的突变株来询问这些基因是否对应于不同的分子或遗传途径。最后，我们将使用这些数据来生成模型，这些模型将使我们能够更好地从理论上理解合作行为是如何维持的，以及进化结果是如何受到限制的。

Although the Darwinian idea of 'survival of the fittest' is central to our understanding of the diversity of life on this planet, the evolution and maintenance of cooperative behaviour remains a conundrum. This is because when cooperating individuals perform some sort of costly act to help one another, they run the risk of disruptive cheaters that do not pay their fair share of the cost. In other words, if cheating is a better strategy, how is cooperative behaviour maintained within populations? In order to better understand this problem, we believe that it will first be important to identify the nature of the genes and pathways that regulate cooperative behaviours. This is because, although evolutionary theory may suggest the best strategy, the genetic changes required may not be possible. For example, some strategies may not exist because any gains may be offset by other fitness costs. Alternatively, the genes and pathways that they regulate behaviour may be organised in such a way that it simply is not be possible for evolution to mould them achieve the optimal or favoured strategy. In this grant, we propose to address each of these problems using a simple system for the study of cooperative behaviour, the soil dwelling social amoeba D. discoideum. Under favourable conditions, D. discoideum amoebae exist as single celled individuals that grow and divide by feeding on bacteria. Upon starvation, however, up to 100,000 amoebae aggregate and cooperate to make a multicellular fruiting body consisting of hardy spores supported by dead stalk cells. Stalk cells thus sacrifice themselves to help the dispersal of spores, raising the question of why selection does not lead to unchecked cheating by individuals that do not pay their fair share of the cost of stalk production. To achieve this goal, we will employ a novel combination of approaches in D. discoideum that allow cooperative behaviour to be analysed with great power. We have recently found that even within a small number different D. discoideum strains, different social strategies could be detected. The work described in this proposal, will allow us to define and classify the number of the strategies within a larger set of strains, because this can be used to determine the number of different 'ways' evolution has allowed social strategies to be modified. We will then ask whether these correspond to distinct molecular or genetic pathways by searching for mutant strains with altered social behaviour. Finally, we will use these data to generate models that will allow us to develop a better theoretical understanding of how cooperative behaviour is maintained and evolutionary outcomes constrained.