Social preferences of three-spined sticklebacks: A mesocosm experiment

Determining the social structures within populations and identifying the factors that influence them can be of great value for understanding behavioural ecology and evolution. Animals often exhibit preferences for joining certain groups and preferentially associate with some individuals over others, resulting in non-random group compositions. Since group composition can affect fitness components such as predation risk and foraging success, it is important to understand how these social preferences arise. Here, we report on an experimental study that strives to identify the role and relative importance of factors that determine shoaling decisions in three-spined sticklebacks (Gasterosteus aculeatus). The purpose of this study is to investigate shoaling under more natural conditions, where fish are able to assort freely. To this end, we raised a cohort of three-spined sticklebacks, for which we manipulated social group size and perceived predation risk following a two-factorial design. We then introduced PIT (passive integrated transponder) tagged fish from different treatments into a mesocosm system consisting of several connected semi-natural ponds equipped with RFID (radio-frequency identification) antennas. This system allows for remote, continuous, and long-term tracking of the location and movement of each fish, and thus offers unique insights into their social decisions. In this way, we intend to investigate how social preferences and shoaling decisions of sticklebacks are influenced by factors such as body size, prior familiarity, early-life conditions, and personality. We will present the first results of this mesocosm experiment, which should provide better understanding of the organisation of social interactions and their underlying mechanisms.