Lifetime reproductive success and longevity of workers in a social insect

社会行为的进化和老龄化的进化都是进化生态学的主要研究领域。社会行为的进化涉及动物社会如何产生和维持，例如真社会昆虫(蚂蚁、蜜蜂、黄蜂和白蚁)的社会。衰老的演变涉及影响生物体寿命的因素和其一生中的繁殖模式。最近，研究人员意识到，这些领域是相互关联的，而传统的老龄化模式可能会受到社会性的严重影响。一个关键的例子涉及终生生殖成功(一个人一生中生育的后代数量)与寿命之间的关系。标准的衰老进化理论预测，外部死亡的来源(外部环境中导致死亡的因素，如捕食者、事故等)选择更早的繁殖，这反过来又由更早的死亡来支付。这预示着一生的生殖成功和寿命之间存在负相关关系，即生育更多后代的个体寿命更短。但是，在同时包含繁殖和帮助个体的社会中，研究人员预测，繁殖者应该在一生的繁殖成功和寿命之间表现出积极的关系，即产生更多后代的个体寿命更长。这是因为在社会性社会中，繁殖者通过留在巢中免受外在死亡的影响。首席研究员最近的研究证实了这一预测，首次证明了一种共生昆虫--大黄蜂--蜂王的一生繁殖成功与寿命之间存在正相关关系。在熊蜂中，就像许多其他共生昆虫一样，工蜂都是蜂后的女儿，可以产生一些自己的后代。由于蜜蜂的性别决定系统，工人的后代总是雄性。生殖工作者和蜂王一样，如果倾向于留在巢中，就不会受到外部死亡的保护，但如果它们经常离开巢去觅食，就不会受到保护。这使得外部死亡的假设效应得以隔离，因为它导致了这样的预测，即如果生殖工作者倾向于留在巢中，他们的一生繁殖成功与寿命之间将呈现正向关系，而如果他们倾向于离开巢去觅食，则呈现负向关系。这个项目的目的是以白背飞虱为研究对象来验证这一假说。该项目是可行的，因为白背飞虱是一种一年一度的群居昆虫，即在一个季节完成其群体周期的昆虫，因此蜂王和工蚁在群体中最多生活几个月。B.terrestris菌落也是商业上可用的，很容易在实验室里保存和观察。所有母蚁后及其生殖工作者女儿的一生繁殖成功和寿命将在一组蜂群中确定，这些蜂群的工作者已被单独标记。出生和死亡日期、在巢中度过的时间和一生的繁殖成功将在所有个体中进行衡量，终身繁殖成功将通过产卵量(通过拍摄巢穴来衡量)和使用遗传标记的雄性亲子关系分析来衡量。这项研究具有新颖性和基础性，因为它将在社会演变和老龄化演变的重要领域的交界处检验新概念。出于这个原因，这项工作将极大地促进我们对社会性和老龄化的基本理解。

The evolution of social behaviour and the evolution of ageing both form major areas of study in evolutionary ecology. The evolution of social behaviour concerns how animal societies such as those of the eusocial insects (ants, bees, wasps and termites) arise and are maintained. The evolution of ageing concerns the factors that affect the longevity of organisms and the pattern of reproduction over their lifetimes. Recently, researchers have realised that these areas are connected, and that orthodox patterns of ageing can be heavily affected by sociality. A key example involves the relationship between lifetime reproductive success (the number of offspring an individual has over its lifetime) and longevity. The standard evolutionary theory of ageing predicts that sources of extrinsic mortality (factors leading to death in the external environment, such as predators, accidents, and so on) select for earlier reproduction, which in turn is paid for by earlier death. This predicts a negative relationship between lifetime reproductive success and longevity, i.e. that individuals producing more offspring have shorter lives. But, in eusocial societies, which contain both breeding and helping individuals, researchers have predicted that the breeders should exhibit a positive relationship between lifetime reproductive success and longevity, i.e. that individuals producing more offspring have longer lives. This is because breeders in eusocial societies are protected against extrinsic mortality by remaining in the nest. The principal investigator's research recently confirmed this prediction by demonstrating for the first time a positive relationship between lifetime reproductive success and longevity in queens of a eusocial insect, the bumble bee Bombus terrestris.In B. terrestris, as in many other eusocial insects, the workers, which are all daughters of the queen, can produce some offspring of their own. Because of the sex determination system in bees, workers' offspring are always males. Reproductive workers will, like queens, be protected from extrinsic mortality if they tend to remain in the nest, but not if they routinely leave the nest to forage. This allows the hypothesized effect of extrinsic mortality to be isolated, because it leads to the prediction that reproductive workers will exhibit a positive relationship between lifetime reproductive success and longevity if they tend to remain in the nest and a negative relationship if they tend to leave the nest to forage. The aim of this project is to test this hypothesis using B. terrestris as the study organism.The project is feasible because B. terrestris is an annual eusocial insect, i.e. one completing its colony cycle in a single season and hence one in which queens and workers live in the colony for at most a few months. B. terrestris colonies are also commercially available and are easy to keep and observe in the laboratory. The lifetime reproductive success and longevity of all mother queens and a sample of their reproductive worker daughters will be determined in a set of colonies whose workers have been individually marked. Birth and death dates, time spent in the nest and lifetime reproductive success will be measured across all individuals, with lifetime reproductive success being measured both as egg-production (measured from filming of nests) and from parentage analyses of males using genetic markers. This research is novel and fundamental because it will test new concepts at the interface of the important areas of social evolution and the evolution of ageing. For this reason, the work will substantially advance our basic understanding of both sociality and ageing in general.