Phenotype-dependent schooling behaviour across hierarchical levels in three-spined sticklebacks
Schooling is a widespread behaviour among pelagic fish that reduces locomotion costs of migration and predation risk. It is characterised by coordinated movements, speed and orientation of group members. Although schooling can vary both between populations and among individuals of the same population, these levels of variation are seldom considered together. Here, we investigated whether…
Schooling behaviour, a common occurrence among pelagic fish, benefits migratory fish by reducing migration costs and predation risk. This behaviour is characterized by coordinated movements, speed, and orientation of group members. However, schooling can differ between populations and among individuals within populations, yet these variations are often considered separately.
This study examined whether schooling tendencies in three-spined sticklebacks (Gasterosteus aculeatus) differ between populations and among individuals within populations, based on their phenotype.
The researchers initially compared the schooling behaviour of anadromous (migrating) sticklebacks and recently landlocked (resident) sticklebacks, assessing whether individual sociability influenced within-population variation in schooling. Subsequently, they investigated how schooling behaviour might be affected when migrants and residents are mixed together.
Migrant groups exhibited superior schooling performance compared to resident groups, with higher alignment. Within migrant groups, less social individuals assumed more leadership roles, displayed better alignment, swam closer to others, and fatigued less than more social fish. These patterns were not observed in resident groups.
When the two populations were combined, overall schooling performance decreased, particularly among migrants, with schools showing reduced compaction and alignment, similar to resident groups. The study concluded that individuals did not adjust their schooling behaviour according to the social composition of the group, and phenotype-dependent schooling patterns were disrupted in migrants when they were mixed.
These findings suggest that post-isolation, migration-related behaviours can rapidly disappear. Furthermore, the research emphasizes the significance of individual sociability in self-organisation and the emergence of collective behaviour, particularly in populations that retain migratory tendencies. Thus, considering behavioural variation across multiple hierarchical levels is crucial for understanding complex social systems.
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