Helpers at the nest
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Helpers at the nest is a term used in behavioural ecology and evolutionary biology to describe a social structure in which juveniles, of one or both sexes, remain in association with their parents and help them in raising subsequent broods or litters, instead of dispersing and beginning to reproduce themselves. This phenomenon was first studied in birds, and is found, for example, in the Common Moorhen, but it is now known in animals of many different groups. It is a simple form of co-operative breeding.
Three explanations for the occurrence of helpers at the nest have been put forward; they are not mutually exclusive, and in any particular species an investigation of the exact benefits and costs will be needed to see what combination of these factors may have driven the evolution of helping.
- Immediate advantage to the helpers, who may be protected from predation, or may gain skills that they will need when they subsequently reproduce, as a result of staying in the parental nest.
- Kin selection: since subsequent litters or broods from the same parents will be full siblings to the helpers, they are as closely related genetically as their own offspring would be. Helping their parents is therefore as productive for the juveniles as reproducing themselves would be, and if their parents are better able to reproduce, the balance of advantage may be greater.
- Delayed advantage to the helpers, in particular because they stand to inherit their parents' territory; this explanation is particularly compelling if suitable territories are in short supply, but requires specific quantitative conditions to be met, favouring a stable queue of potential heirs.
Juveniles living in association with their parents cannot automatically be regarded as helpers; it is necessary to demonstrate that the reproductive success of their parents is increased by their presence (in the Percula Clownfish, for example, it is not). However the delayed advantage explanation for the juveniles' association with their parents can still work in the absence of effective helping, whereas the kin selection explanation cannot.
References
- Wiley, R. H., & Rabenold, K. N. (1984). The evolution of cooperative breeding by delayed reciprocity and queuing for favorable social positions. Evolution, 38, 609-621.