Conflict resolution in mutualisms.

许多生物与其他物种有着密切的联系。一般来说，较小的伙伴(共生)部分生活在较大的伙伴(东道主)身上。共生可能对双方都有利，在这种情况下，它们被称为互惠，或者可能涉及一个伙伴(寄生虫)对另一个伙伴(宿主)造成伤害。即使双方似乎都从这种联系中受益，他们也并不总是拥有相同的进化利益。寄生和互惠之间没有一成不变的边界，重要的是要了解哪些因素有利于共生体对宿主的积极或消极影响。如果共生菌只是在某些情况下寄生，就像在许多动物的微生物感染中一样，情况尤其如此。更广泛地说，互惠互利在生物学中具有巨大的重要性，无论是在短期还是长期。例如，它们与根瘤菌的联系使豆类植物能够获得氮素。互惠互利也可以导致重大的进化事件，我们细胞的两个主要遗传成分(细胞核和线粒体)起源于一种古老的互惠互利。尽管互惠互利很重要，但没有通用的理论来解释我们应该在什么时候期待互利的结果，或者互惠互利的人如何解决他们的冲突。然而，越来越多的证据表明，宿主可以通过控制共生体对关键宿主资源的访问，并影响不同个体共生体相互竞争获取宿主资源的方式，来限制共生体的寄生倾向。这种类型的解释可能适用于各种情况，包括植物和传粉者、植物和固氮菌，甚至一些人类疾病。这个项目将使用一个涉及无花果树和授粉黄蜂的模型系统来研究寄主如何控制它们的共生体。这是一种互惠互利的互动，但存在明显的冲突。具体地说，虽然无花果需要黄蜂为它们的花授粉，但黄蜂的幼虫会吃掉一些无花果种子。无花果需要管理黄蜂，这样它们就不会在所有的种子中产卵。无花果可能会通过改变无花果花的质量和结构来管理黄蜂，使其中一些花成为黄蜂产卵的更理想地点。这可能是因为一些花是黄蜂幼虫发育的更好场所，或者是因为一些花更容易让黄蜂产卵，或者两者兼而有之。理论上，黄蜂对某些花的偏爱，加上它们浪费时间拒绝它们认为不适合的花，或者其他黄蜂已经产卵的花(每朵花只能发育一个卵)，可以防止黄蜂利用太多的种子，并允许互惠关系持续下去。我们将通过对五对无花果及其传粉者进行详细研究来测试这一想法，选择这些物种来反映世界上750多种无花果在生物学上的巨大差异。我们将拍摄和分析黄蜂的寻花和产卵行为，并评估某些花朵是否会产生更好的(更大的)黄蜂后代。我们将使用这些数据来检验每个物种的理论模型。我们还将通过测量进入无花果的平均黄蜂数量、每只黄蜂的平均卵数以及这些卵子可能利用的平均花朵数量，来估计在每种情况下无花果和黄蜂伙伴之间的冲突程度。此外，我们将调查一些无花果物种是否使用上述机制之外的额外机制(如快速花枯萎)来阻止黄蜂产卵过多。总体而言，该项目将详细调查不同的无花果物种如何阻止它们的传粉者破坏它们所有的种子(从而使互惠关系得以持续)，使用一种新的方法，应该不仅有助于我们理解这些，而且可能有助于我们理解大多数互惠关系。

Many organisms are involved in intimate associations with other species. In general the smaller partner (symbiont) lives partly in or on the larger partner (host). Symbioses can be beneficial to both partners, in which case they are called mutualisms, or can involve one partner (the parasite) inflicting harm on the other (host). Even when both partners appear to gain from the association, they do not always have the same evolutionary interests. There is no hard and fast border between parasitism and mutualism and it is important to understand what factors favour positive or negative effects of the symbiont on the host. This is especially so if the symbiont is only parasitic under certain circumstances, as in many microbial infections of animals. More generally, mutualism is of immense importance in biology, both in the short and long term. For example, their association with rhizobial bacteria allows bean plants access to nitrogen. Mutualism can also lead to major evolutionary events and the two major genetic components of our cells (nucleus and mitochondria) had their origins in an ancient mutualism. Despite the importance of mutualism, there is no general theory that explains when we should expect a mutualistic outcome, or how the mutualists resolve their conflicts. However, there is increasing evidence that hosts can limit the parasitic tendencies of symbionts by controlling their access to key host resources and also influencing the way in which different individual symbionts have to compete with each other for access to host resources. This type of explanation could be applicable in a wide variety of cases including plants and pollinators, plants and nitrogen-fixing bacteria, and even some human diseases. This project will investigate how hosts control their symbionts using a model system involving fig trees and their pollinating wasps. This is a mutualistic interaction, but one with clear conflicts. Specifically, while figs need wasps to pollinate their flowers, the wasp larvae eat some of the fig seeds. The fig needs to manage the wasps so that they do not lay eggs in all the seeds. Figs may manage wasps by altering the quality and architecture of the fig flowers so that some are more desirable sites for wasp to lay eggs. This may be because some flowers are better places for wasp larvae to develop, or because some flowers are easier for wasps to lay eggs into, or both. In theory, the wasps' preference for certain flowers, plus the fact that they waste time rejecting flowers that they deem unsuitable, or flowers in which other wasps have laid eggs (only one egg can develop per flower), can prevent the wasps from exploiting too many of the seeds and allow the mutualism to persist. We will test this idea by making detailed studies of five pairs of figs and their pollinators, choosing the species to reflect the great differences in biology seen across the over 750 species of figs in the world. We will video and analyse the flower searching and egg-laying behaviour of wasps and also assess whether certain flowers give rise to better (bigger) wasp offspring. We will use the data to test the theoretical model for each species. We will also estimate just how much conflict there is between the fig and wasp partners in each case, by measuring the average number of wasps entering a fig, the average number of eggs per wasp, and the average number of flowers that these eggs could potentially exploit. In addition, we will investigate whether some fig species use extra mechanisms (such as rapid flower wilting) beyond those mentioned above to stop wasps laying too many eggs. Overall, the project will be a detailed investigation of how diverse fig species stop their pollinators from destroying all their seeds (thus allowing the mutualism to persist), using a new approach that should help us to understand not only these, but perhaps most mutualisms.