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

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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.