Cooperation represents an evolutionary puzzle because natural selection is thought to favour selfish individuals over co-operators. However, theoretical studies and studies in humans show us that co-operators are preferred as social and sexual partners. Partner choice may therefore provide an important explanation for the evolution and stability of cooperation, alongside other known mechanisms, such as kin selection and self-serving benefits. However, we lack an understanding of whether partner choice is an important mechanism favouring cooperation in natural systems. Recent studies in captivity and some natural systems showed that animals prefer to associate with more cooperative individuals. An unequivocal test of the importance of partner choice would be to manipulate cooperation in the wild and test the associated fitness consequences. This project is pursuing this goal by combining a series of innovative experiments with a long-term study established on a highly cooperative wild bird, the sociable weaver Philetairus socius. New methodological developments are allowing us to conduct large-scale experiments in the wild and through detailed long-term tracking of individuals we can quantify life-long fitness consequences of choice. Specifically, here we are : i) using a new conceptual framework to test whether cooperative behaviour is reliable (e.g. repeatable or associated with the birds’ body condition, which is a prerequisite for being used in partner choice); ii) use state-of-the-art technology to manipulate cooperative behaviour and measure the resulting patterns of social and sexual partner choice; iii) use lifetime reproductive success and monitoring of experimental individuals over several years to examine the fitness benefits of partner choice for both co-operators and the individuals that associate with them. Finally, we will be using physiological measures (such as telomere dynamics) to investigate the mechanisms underlying the changes in fitness. Our ultimate aim is to provide a novel and robust evaluation of the roles of social and sexual selection on the evolution and maintenance of cooperation that can help us to understand the mechanisms underlying cooperation in nature, from invertebrates to humans.
