The evolution of cooperation among unrelated individuals: experimental field studies in a group-living bird.

• Applicant: Privatdozent Michael Griesser, Ph.D.
• Subject Area: Evolution, Anthropology ; Sensory and Behavioural Biology ; Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
• Term: from 2020 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 435683480

Cooperation is pivotal for the evolution of biological complexity but challenges traditional views of natural selection. Why should individuals engage in costly behaviours that benefit others? Past work has shown that indirect benefits facilitate cooperation among kin, while direct fitness benefits facilitate cooperation independent of kinship. Cooperation based on direct fitness benefits is usually attributed to reciprocity, which, however, is rarely documented empirically. Therefore, it remains unknown how cooperative interactions are initiated, particularly when involving delayed benefits to actors that provide recipients with opportunities for deception. Enduring cooperation could be explained by interdependence that arises when individuals contribute to shared resources (territory, predator protection), and hence, their fitness becomes increasingly intertwined. This mechanism may facilitate the formation of social bonds. Indeed, work in primates has suggested that strong social bonds are an expression of strong interdependence, but this idea has never been tested experimentally. Here I propose an integrative research program to investigate the drivers, mechanisms and consequences of interdependence in a long-term population of wild Siberian jays (Q1-3). I will further address this using comparative work (Q4). I will focus on unrelated, same-sex dyads of breeders and non-breeders, where interdependence is not based on shared genes or investment into a potential mate, and address four questions:Q1) Cooperating in the face of danger? Develop a robust measure of interdependence using existing data in a social network framework. Use observations and experiments to test if a high local predation risk and a high rate of conflicts with neighbouring groups govern interdependence between individuals.Q2) What is the hormonal mechanism governing interdependence? Establish this by measuring the levels of relevant hormones (mesotocin, vasotocin) in same-sex dyads that differ in their interdependence. Confirm the hormonal mechanism experimentally using intranasal administrations of the hormone identified. Q3) What are the short- and long-term benefits of interdependence? Use experiments of Q1-2 and long-term population data to answer this question. Provide the first experimental test of the hypothesis that a high number of close social bonds (i.e., high interdependence) is associated with lower levels of stress hormones in demanding situations, resulting in a higher lifetime fitness. Q4) Which ecological and life-history factors govern interdependence in birds and mammals? Answer this question using phylogenetic comparative models relying on published data. Assess the ecological and life-history correlates of maternal and allomaternal care, which in primates facilities the evolution of cooperation also among unrelated individuals.

• DFG Programme: Research Grants