Kin-selected conflict and the evolution of lifespan and ageing

为什么有机体会衰老，也就是说，当它们变老的时候会变得更虚弱，这是进化生态学的一个中心话题。既然身体可以自我修复，为什么每一个有机体不能不断地自我更新，并保持在高峰状态，尽管它的年龄？衰老的进化理论用自然选择回答了这个问题。事故不可避免地使老年人比年轻人少。这意味着老年人对后代的遗传贡献较小。反过来，这意味着自然选择对它们的重视程度较低，或者换句话说，具有有害影响的基因在老年个体中的选择性较低。结果是选择老化。然而，这种关于老龄化演变的传统观点是不完整的，因为它忽略了社会影响。通常情况下，一个人的死亡只会使那些不相关的同类受益，他们可以获得它留下的资源。但是在一个由亲属群体组成的种群中，一个个体的死亡会使其相关的群体成员受益。这通过亲属选择影响寿命和衰老的进化，即因为亲属共享共同的基因。一个例子是自然界中常见的情况，父母的死亡释放了一种资源，如巢或领土，需要后代繁殖（资源继承）。最终，这对后代有利，为父母过早死亡创造了激励，但有一个扭曲;父母和后代在父母死亡和资源移交的确切时间上并不“同意”。当父母死亡时，它有效地“交易”自己的后代（相关性，r = 0.5），以换取其年轻人的后代，即其grandofspring（r = 0.25）。但是后代会用它的兄弟姐妹（r = 0.5）交换它自己的，同样相关的后代（r = 0.5）。由此可见，如果父母的繁殖力下降，那么后代会在父母放弃资源之前优先继承资源，因此，在满足这些条件的社会系统中，后代会骚扰甚至杀死繁殖力下降的父母。如果亲本的繁殖力下降得足够厉害，那么亲本通过死亡并允许后代繁殖而不是活着来获得更多的适应性。这样的父母会迅速衰老和死亡。在这项建议中，我们的目标是测试的假设，亲属选择冲突的资源继承影响寿命和老化使用熊蜂terrestris作为我们的实验系统。这一物种非常适合这项工作，因为工蜂从它们的母亲--蚁后那里继承了巢穴，并在里面繁殖自己的后代。terrestris工蜂有时会在繁殖前杀死自己的母亲（工蜂杀母）。我们将检验该假说的两个核心预测。第一种是，工蜂骚扰蜂后，当它们认为繁殖后代比饲养蜂后和养育兄弟姐妹能获得更大的适应力时，就会杀死蜂后。第二，在或接近阈值时，女王被选中将巢穴的控制权交给工人，女王老化应该加速。为了验证第一个预测，我们将进行实验，例如比较有和没有侵略性的，潜在的生殖工人的女王的寿命。为了检验第二个，我们将证实已知在其他社会性昆虫中作为衰老指标的基因在B中也起着同样的作用。terrestris。然后，我们将测试在被工蚁骚扰的蚁后中，这些基因的表达水平是否会发生变化，从而表明它们加速衰老。拟议的研究是新颖的，因为焦点假设以前没有经过测试，也没有一个结合的行为和遗传的方法来调查这些问题被实施。这是根本性的，因为理解社会性如何影响老龄化在理论和实践上都很重要。因此，这项工作应产生对若干学科有价值和相关性的结果。

Why organisms age, i.e. grow feebler, as they grow old is a central topic in evolutionary ecology. Since bodies self-repair, why cannot every organism constantly renew itself and remain at peak condition despite its chronological age? The evolutionary theory of ageing answers this question with natural selection. Accidents inevitably ensure that there are fewer old individuals than young ones. This means that old individuals make a smaller genetic contribution to future generations. In turn, this means that natural selection values them less highly, or, put another way, that genes with harmful effects are less strongly selected against in older individuals. The result is selection for ageing. However, this conventional view of the evolution of ageing is incomplete, because it omits social effects. Normally an individual's death benefits only the unrelated conspecifics who gain access to the resources it leaves behind. But in a population made up of groups of relatives, death of one individual benefits its related group-mates. This affects the evolution of lifespan and ageing through kin selection, i.e. because relatives share genes in common. An example is the case, common in nature, of a parent whose death releases a resource, such as a nest or territory, required by an offspring to breed (resource inheritance). Eventually this benefits the offspring, creating an incentive for the parent to die prematurely, but there is a twist; parent and offspring do not 'agree' on the exact timing of parental death and resource handover. When the parent dies, it effectively 'trades' its own offspring (relatedness, r, = 0,5) for the less-related offspring of its young, namely its grandoffspring (r = 0.25). But the offspring trades its siblings (r = 0.5) for its own, equally-related offspring (r = 0.5). It follows that, if the parent is declining in fecundity, the offspring favours inheriting the resource before the parent favours yielding it. So, in social systems meeting these conditions, offspring should harass and even kill a parent whose fecundity is declining. If parental fecundity declines sufficiently, the parent gains more fitness by dying and allowing the offspring to reproduce than by remaining alive. Such a parent should rapidly age and die. In this proposal, we aim to test the hypothesis that kin-selected conflict over resource inheritance affects lifespan and ageing using the bumble bee Bombus terrestris as our experimental system. This species is highly suitable for the work because workers inherit the nest from their mother, the queen, and produce their own offspring within it. In addition, B. terrestris workers do sometimes kill their own mother before reproducing (worker matricide). We will test the two central predictions of the hypothesis. The first is that workers harass the queen and commit matricide when they assess that they will gain greater fitness from offspring production than from keeping the queen alive and rearing siblings. The second is that, at or approaching the threshold when the queen is selected to cede control of the nest to workers, queen ageing should be accelerated. To test the first prediction, we will carry out experiments such as comparing the lifespans of queens with and without aggressive, potentially reproductive workers. To test the second, we will confirm that genes known to be indicators of ageing in other social insects act likewise in B. terrestris. We will then test whether, in queens being harassed by workers, these genes show changes in expression level indicating accelerated ageing. The proposed research is novel because the focal hypothesis has not previously been tested, and nor has a combined behavioural and genetic approach to investigating such issues been implemented. It is fundamental because of the theoretical and practical importance of understanding how sociality affects ageing. The work should therefore yield results of value and relevance to several disciplines.