Abstract
Individuals are different, but they can work together to perform adaptive collective behaviours. Despite emerging evidence that individual variation strongly affects group performance, it is less clear to what extent individual variation is modulated by participation in collective behaviour. We examined light avoidance (negative phototaxis) in the gregarious cockroach Blaberus discoidalis, in both solitary and group contexts. Cockroaches in groups exhibited idiosyncratic light-avoidance performance that persisted across days, with some individual cockroaches avoiding a light stimulus 75% of the time, and others avoiding the light just above chance (i.e. ∼50% of the time). These individual differences were robust to group composition. Surprisingly, these differences did not persist when individuals were tested in isolation, but returned when testing was once again done in groups. During the solo testing phase cockroaches exhibited individually consistent light-avoidance tendencies, but these differences were uncorrelated with performance in any group context. Therefore, we have observed not only that individual variation affects group-level performance, but also that whether or not a task is performed collectively can have a significant, predictable effect on how an individual behaves. That individual behavioural variation is modulated by whether a task is performed collectively has major implications for understanding variation in behaviours that are facultatively social, and it is essential that ethologists consider social context when evaluating individual behavioural differences.
Highlights
IntroductionWe need to examine the relationship between individual variation and collective behaviour
Our results demonstrate that cockroaches have individually consistent variation in shade tracking performance (Figs 1-2)
We show that this idiosyncratic cockroach behaviour is robust to group composition (Fig 3) and is consistent over the course of several weeks (Fig 5), but surprisingly does not persist when cockroaches are tested in isolation from a group (Fig 4)
Summary
We need to examine the relationship between individual variation and collective behaviour This relationship is complex, and is currently a frontier of research in animal behaviour Castes within eusocial insects are a classical example of behavioural differentiation within a group context (O’Donnell 1998; Winston & Michener, 1977) These differences can emerge even when all individuals are genetically identical (Freund et al, 2013), suggesting that individual variation in behaviour could be an emergent property of group membership.
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