Bilateral BBSRC-FAPESP: A genome wide view of the evolutionary processes shaping genetic variation in natural populations

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。然而，如果只有适者生存和繁殖，那么为什么我们会看到个体之间在与适应性相关的特征上有如此多的差异？这个问题在社会系统中尤为突出，在这些系统中，合作的个体会做出某种帮助他人的代价高昂的行为。因此，合作行为对个人和与他们互动的人（通常是他们的亲属）的健康有重要影响。此外，合作的个人面临着破坏性作弊者入侵的风险，这些作弊者从合作行为中获益，但不支付其公平的成本份额。在这种情况下，我们会期望出现“最佳”策略：要么作弊，要么合作。然而，令人惊讶的是，对自然群体的研究往往揭示出个体合作和欺骗程度的差异。如果作弊或合作是更好的策略，那么为什么合作者-作弊者连续体中会有沿着的变化呢？为了更好地理解这个问题，我们认为不仅要描述种群中实际存在的变异的性质，还要描述产生这种变异的基因以及形成变异的过程。这是因为，尽管进化理论可能提出了最佳策略，但所需的遗传变化可能是不可能的。例如，某些策略可能不存在，因为任何收益都可能被其他适应度成本抵消。或者，合作性状可能很少表达，或者可能有有限的机会作弊，因此，达尔文选择的行动可能只是太低效的模具变化，以实现最佳或青睐的strategy.We建议解决这个基本问题，使用一个简单的系统，合作行为的研究，土壤中居住的社会变形虫Dictyosteelium discoideum。在有利条件下，D.盘状变形虫以单细胞个体存在，通过以细菌为食而生长和分裂。然而，在饥饿时，多达100，000个变形虫聚集并合作形成多细胞子实体，其由死柄细胞支持的哈代孢子组成。因此，茎细胞牺牲自己来帮助孢子的传播。这种牺牲可能是有利的，因为它们通常帮助亲属，但当非亲属互动时，个人的牺牲可能会帮助非亲属。至关重要的是，像其他系统一样，我们发现D。盘状突在一系列广泛的特征中表现出巨大的多样性，包括不同个体合作的程度，从而为我们提供了一个简单的系统来调查为什么会存在这种变异。为了实现这一目标，我们将采用一种新的组合的方法在D。这些基因可以让合作行为和其他特征的遗传和进化得到强大的分析。我们将使用大量的自然发生的菌株来鉴定基因中的自然变异，这些变异解释了我们观察到的性状的多样性。我们将描述产生社会特征自然多样性的基因类型，并询问这些基因是否也影响其他类型的非社会特征，这可能表明它们受到非社会过程的约束或塑造。我们将能够确定进化过程的类型，这些过程似乎对种群中变异的维持或持续负有责任。最后，我们将把这些结果与进化模型相结合，以更好地从理论上理解遗传多样性是如何维持的，进化结果是如何受到限制的。因此，这项工作将导致一个根本性的进步，在我们的理解类型的变异基础上的表型多样性在自然种群和进化过程中形成的变化。

The Darwinian idea of 'survival of the fittest' is central to our understanding of the diversity of life on this planet. However, if only the fittest survive and reproduce, then why do we see so much variation among individuals in traits that are tied to fitness? This problem is especially striking in social systems where cooperating individuals perform some sort of costly act that helps others. Cooperative behaviour therefore has important effects on the fitness of individuals and those that they interact with (often their relatives). Furthermore, cooperating individuals run the risk of invasion by disruptive cheaters that reap the benefits of cooperative behaviours, but do not pay their fair share of the cost. In such situations, we would expect the 'best' strategy to emerge: either cheating or cooperating. Surprisingly, however, studies of natural populations often reveal variation in the degree to which individuals appear to cooperate and cheat. If either cheating or cooperating is the better strategy, then why is there variation along a cooperator-cheater continuum? To better understand this problem, we believe that it is important to not only describe the nature of the variation that is actually present in populations, but also the genes that generate this variation and the processes shaping their variation. 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, cooperative traits may be expressed rarely, or there may be limited opportunities to cheat, and as a result the action of Darwinian selection may simply be too inefficient to mould variation to achieve the optimal or favoured strategy.We propose to address this fundamental question using a simple system for the study of cooperative behaviour, the soil dwelling social amoeba Dictyostelium 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. Such sacrifices can be favoured because they typically help relatives, but when non-relatives interact, the sacrifices of an individual may help non-relatives. Crucially, like other systems, we have discovered that D. discoideum show enormous diversity in a wide array of traits, including the degree to which different individuals cooperate, thus providing us with a simple system to investigate why such variation exists. To achieve this goal, we will employ a novel combination of approaches in D. discoideum that allow the genetics and evolution of cooperative behaviour and other traits to be analysed with great power. We will use a large panel of naturally occurring strains to identify natural variation in genes that account for the diversity in the traits we observe. We will characterize the types of genes that produce natural diversity in social traits and ask whether those genes also affect other types of non-social traits, which could suggest that they are constrained or shaped by non-social processes. We will be able to determine the types of evolutionary processes that appear to be responsible for the maintenance or persistence of variation in populations. Finally, we will integrate these results with models of evolution to develop a better theoretical understanding of how genetic diversity is maintained and evolutionary outcomes constrained. This work will therefore lead to a fundamental advance in our understanding of the types of variation underlying phenotypic diversity in natural populations and the evolutionary processes shaping that variation.