Genetic architecture and constraint in social evolution

尽管达尔文的“适者生存”思想是我们理解这个星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，当合作的个体采取某种代价高昂的行动来帮助彼此时，他们就会冒着被不支付其公平份额的破坏性骗子所欺骗的风险。换句话说，如果欺骗是一种更好的策略，那么合作行为是如何在群体中维持的呢？为了更好地理解这个问题，我们认为首先确定调节合作行为的基因和途径的性质是很重要的。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，因为任何收益可能被其他适合度成本抵消。或者，它们调节行为的基因和途径可能以这样一种方式组织起来，即进化根本不可能塑造它们以达到最佳或有利的策略。在这项资助中，我们建议使用一个简单的系统来研究合作行为，即居住在土壤中的社会变形虫D.盘状变形虫，来解决这些问题。在有利条件下，盘状变形虫以单细胞个体的形式存在，以细菌为食生长和分裂。然而，在饥饿的情况下，多达10万只变形虫聚集并合作形成多细胞子实体，由死亡的茎细胞支持的耐寒孢子组成。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：为什么选择没有导致那些不支付其公平份额的茎生产成本的个体肆无忌惮的欺骗？为了实现这一目标，我们将采用一种新颖的方法组合来分析盘状天竺鼠的合作行为。我们最近发现，即使在少数不同的盘状棘球蚴菌株中，也可以检测到不同的社会策略。本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，我们将通过寻找改变社会行为的突变菌株来询问这些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约束的。

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.