Is nest-drifting behaviour an insurance policy for maximising indirect fitness in primitively eusocial paper wasps?

达尔文的自然选择理论预言，为了将尽可能多的基因传递给下一代，生物体的行为应该是自私的。社会行为的进化是一个悖论，因为它要求一些个体放弃繁殖，以帮助抚养其他个体的后代。自达尔文以来，解释动物社会中帮助行为的进化一直是进化生物学家的主要关注点。一种主流的解释是，帮助者从抚养亲属的后代中获得净收益。这个项目将研究最近发现的一种帮助群居昆虫的策略，并询问它是否可以用保险单来解释。群居昆虫（蜜蜂、黄蜂、蚂蚁和白蚁）通常以亲戚的形式生活，帮助者从抚养相关的后代中获益。因此，生物学家们感到困惑的是，他们偶尔会发现“帮手”们漂向自己以外的巢穴。漂移的发生是否有其原因一直存在争议：有时巢漂移似乎是偶然的，但在其他情况下，漂流者会在他们访问的巢中产卵。最近，在群居纸黄蜂中发现了一种新的漂泊解释：一个种群中超过一半的黄蜂会访问几个相关的巢穴，从一个巢穴漂流到另一个巢穴，传递饲料并喂养后代。这种行为在助人的进化过程中有着重要的意义，但迄今为止一直被忽视。这个项目探讨了这个问题。首先，该项目将确定漂流者是否会根据每个巢穴的回报将他们的帮助分配到不同的巢穴中，就像你可能会换一份工作，做同样多的工作，赚更多的钱一样。漂流者也许能够对帮助他人的回报变化做出反应，从而使他们的基因适应性最大化。然而，如果通过换巢，漂鸟丧失了它们已经投入的努力，那么漂鸟从这个策略中得到的好处就很少。如果你曾经试图抵消你的碳足迹，你就会对这个论点很熟悉。如果你每坐一次飞机就种一棵树，你肯定希望在树木抵消碳排放之前不会被砍倒。基于保证的优势可能以类似的方式解释帮助行为：如果在她死亡或缺席的情况下，那些部分抚养的后代将由剩余的巢穴同伴抚养到成年，那么帮助者应该只提供帮助。这个项目将决定漂流者在几个不同的巢穴中投入的帮助努力是否得到保证，即使他们减少（或撤回）对某个特定巢穴的帮助。漂移行为实际上可能是一种确保投资的机制。为了弥补一名佣工的损失，可以从一群流民中招募新的佣工。没有新成员，部分饲养的幼鸟可能会死亡，帮手的投资也会损失。号召一批现成的新员工，就像一个商人去就业中心填补一个紧急空缺一样。这种形式的招募（对黄蜂和商人来说）比找到一个新手并从头开始训练他们要快得多，成本也低得多。该项目将确定漂流是否是一种保证帮手投资的机制。最后，采取任何策略都需要考虑利弊。例如，在全球经济动荡之际，你可能会考虑是否值得投资股票。同样，群居动物也会权衡帮助他人的成本和收益。例如，如果漂流会导致高死亡率，那么根据回报在不同巢穴之间转换投资的成本往往会超过收益。根据在本项目中获得的漂流成本和收益的估计，最终目标将是确定漂流行为如何改变我们目前对理论背景下帮助行为和社会性进化的理解。

Darwin's theory of natural selection predicts that organisms should act selfishly in order to pass on as many of their genes to the next generation as possible. The evolution of social behaviour is a paradox because it requires that some individuals forgo reproduction in order to help raise the offspring of others. Explaining the evolution of helping behaviour in animal societies has been a major focus for evolutionary biologists ever since Darwin. A leading explanation is that helpers gain a net benefit from raising the offspring of relatives. This project will examine a recently discovered strategy for helping in a social insect, and ask whether it can be explained in terms of an insurance policy. Social insect (bees, wasps, ants and termites) usually live as groups of relatives, where helpers benefit from raising related offspring. Biologists were perplexed, therefore, to find that helpers are occasionally found drifting to nests other than their own. It has been debated whether drifting happens for a reason: sometimes nest-drifting appears to be accidental, but on other occasions drifters lay eggs in the nest they visit. Recently, a new explanation for drifting was discovered in a social paper wasp: over half of the wasps in a population visited several related nests, drifting from nest to nest, delivering forage and feeding the brood. This behaviour has important implications on the evolution of helping, but until now has been neglected. This project explores this question. To begin with, the project will determine whether drifters divide their help amongst different nests in relation to each nest's payoff, in the same way that you might switch to a job that offers more money for the same amount of work. Drifters may be able to respond to changes in the payoffs of helping and so maximise their genetic fitness. If, however, by switching nests drifters forfeit the effort they have already invested, then drifters benefit little from this strategy. You will be familiar with this argument if you have ever tried to offset your carbon footprint. If you plant a tree for every flight you take, you want to be assured that your trees will not be cut down before they have offset your carbon emissions. Assurance-based advantages may explain helping behaviour in a similar way: a helper should only invest help if, in the event of her death or absence, those part-raised brood will be reared to adulthood by remaining nestmates. This project will determine whether the helping effort invested by drifters in several different nests is assured, even if they reduce (or withdraw) their help from a particular nest. Drifting behaviour may actually be a mechanism for assuring investment. To compensate for the loss of a helper, new helpers may be recruited from a pool of drifters. Without new recruits, the part-raised brood may die and the helper's investment lost. Calling on a supply of ready recruits is rather like a businessman going to the job centre to fill an urgent vacancy. This form of recruitment (both for the wasps and the businessman) is much quicker and less costly than finding a novice and training them up from scratch. This project will ascertain whether drifting is a mechanism for assuring investment for helpers. Finally, undertaking any strategy demands a consideration of the pros and cons. For example, you might deliberate whether it is worth investing in stock and shares at a time when the global economy is in turmoil. In a similar way, social animals may weigh up the costs and benefits of helping. For example, if drifting incurs high mortality, then the costs may often outweigh the benefits of being able to switch investment between nests according to payoffs. Based on estimates of the costs and benefits of drifting obtained during this project, the final aim will be to determine how drifting behaviour changes our current understanding of helping behaviour and the evolution of sociality in a theoretical context.