Abstract
Members of numerous animal species show consistent inter-individual differences in behaviours, but the forces generating animal “personality” or individuality remain unclear. We show that experiences gathered solely from social conflict can establish consistent differences in the decision of male crickets to approach or avoid a stimulus directed at one antenna. Adults isolated for 48 h from a colony already exhibit behavioural differences. Prior to staging a single dyadic contest, prospective winners approached the stimulus whereas prospective losers turned away, as they did also after fighting. In contrast, adults raised as nymphs with adult males present but isolated from them as last instar nymphs, all showed avoidance. Furthermore, adults raised without prior adult contact, showed no preferred directional response. However, following a single fight, winners from both these groups showed approach and losers avoidance, but this difference lasted only one day. In contrast, after 6 successive wins or defeats, the different directional responses of multiple winners and losers remained consistent for at least 6 days. Correlation analysis revealed examples of consistent inter-individual differences in the direction and magnitude of turning responses, which also correlated with individual aggressiveness and motility. Together our data reveal that social subjugation, or lack thereof, during post-embryonic and early adult development forges individuality and supports the notion of a proactive–reactive syndrome in crickets.
Highlights
Members of numerous animal species show consistent inter-individual differences in behaviours, but the forces generating animal “personality” or individuality remain unclear
It has become apparent that dominant adult males, in addition to being more aggressive, tend to be more active, more exploratory and more likely to approach a novel stimulus than subordinates (G. bimaculatus[19], G. campestris[23], G. integer[25], Teleogryllus oceanicus26) and that changes in dominance status can erode existing differences (Teleogryllus oceanicus26)
After finding that dominant G. bimaculatus males that won two consecutive dyadic contests in a knockout tournament are more active and exploratory than subordinates that lost two contests, the same traits were found in the prospective winners and losers one day before the tournament[19]
Summary
Members of numerous animal species show consistent inter-individual differences in behaviours, but the forces generating animal “personality” or individuality remain unclear. Much of the pioneering work on invertebrates has focused on adult crickets and documents that both free living and captive members of several species show repeatable inter-individual differences in traits such as aggressiveness, general locomotor activity and exploratory behaviour (Acheta domesticus[17,18], Gryllus bimaculatus[19], Gryllus campestris[20,21,22,23], Gryllus integer[10,24]). The involvement of prior aggressive experience seemed doubtful, since the animals were socially isolated for two days before testing, to negate the well-known effects of winning and losing on subsequent behaviour[28], which at the time were known to last little more than 3 h in crickets[29,30] It was established later, that multiple intermittent defeats lead to practically life-long depression of agonistic behaviour in adult crickets[31,32]. This suggests that differences in adult behaviour in crickets could arise from defeat stress during development, as shown in rodent models for human d epression[37,38], or alternatively as a more general consequence of deprivation of environmental stimulation during isolation[39,40]
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