1. Unconditional versus condition-dependent social immunity.
- Author
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Cremer, Sylvia and Pull, Christopher D.
- Subjects
- *
HERD immunity , *INSECT societies , *DIVISION of labor , *QUEENS (Insects) , *EXTERNALITIES , *REPRODUCTION - Abstract
Cooperation in social animals can lead to collective disease protection beyond individual-level defences, termed 'social immunity.' Social immunity is unconditionally expressed in superorganismal insect colonies with reproductive division of labour between queens and workers. Being obligate altruists, nonreproductive workers fully commit to colony-level disease defence, exhibiting highly specialised and self-sacrificial behaviours. In families of cooperative breeders, all members can reproduce, but offspring delay reproduction to help parents. Here, cooperation, and thus social immunity, is condition-dependent and likely favoured only by high relatedness and low probability of independent reproduction. Inclusive fitness theory is a useful framework to elucidate the relative importance of direct fitness costs of social immunity against indirect fitness benefits of promoting kin health. Socially living animals can counteract disease through cooperative defences, leading to social immunity that collectively exceeds the sum of individual defences. In superorganismal colonies of social insects with permanent caste separation between reproductive queen(s) and nonreproducing workers, workers are obligate altruists and thus engage in unconditional social immunity, including highly specialised and self-sacrificial hygiene behaviours. Contrastingly, cooperation is facultative in cooperatively breeding families, where all members are reproductively totipotent but offspring transiently forgo reproduction to help their parents rear more siblings. Here, helpers should either express condition-dependent social immunity or disperse to pursue independent reproduction. We advocate inclusive fitness theory as a framework to predict when and how indirect fitness gains may outweigh direct fitness costs, thus favouring conditional social immunity. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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