Age-dependent and social status-dependent behavioural plasticity of the cricket Gryllus bimaculatus

Response patterns and underlying neural mechanisms of adaptive behaviours may be similar in different taxa. Among closely related species, this similarity may depend on shared innate motor programs. To test this hypothesis, we analysed the responses of the two-spotted cricket Gryllus bimaculatus to mechanical stimulation of the terminal abdominal appendages (cerci). Final instar juveniles (the last stage of insect larvae) mainly showed escape-like 'dart' responses to stimulation, while a defensive response ('up', 'kick' and 'turn' responses) increased in adult crickets. In older adults, the 'turn' response, in which animals turned towards the stimulus source and jerked their upper body in a threatening raised posture, became more frequent. Thus, the response patterns of crickets to tactile stimulation of the cerci changed from an escape response to a defensive response depending on age and growth. This behavioural plasticity was also dependent on social status. Paired crickets began fighting within 30 s to establish dominance status. Winning juveniles were more likely to show defensive responses and losing adults changed their response from defence to escape. This age- and social status-dependent behavioural plasticity is also observed in crayfish, suggesting a preservation of instinctive behavioural strategies in some arthropods.