Abstract
From invertebrates to vertebrates, a wealth of species display transient sociality during their life cycle. Investigating the causes of dispersal in temporary associations is important to better understand population dynamics. It is also essential to identify possible mechanisms involved in the evolutionary transition from transient to stable sociality, which has been documented repeatedly across taxa and typically requires the suppression of dispersal. In many animals, the onset of dispersal during ontogeny coincides with a sharp decline in social tolerance, but the causal relationship still remains poorly understood. Spiders offer relevant models to explore this question, because the adults of the vast majority of species (>48,000) are solitary and aggressive, but juveniles of most (if not all) species are gregarious and display amicable behaviors. We deployed a combination of behavioral, chemical, and modelling approaches in spiderlings of a solitary species to investigate the mechanisms controlling the developmental switch leading to the decline of social cohesion and the loss of tolerance. We show that maturation causes an increase in mobility that is sufficient to elicit dispersal without requiring any change in social behaviors. Our results further demonstrate that social isolation following dispersal triggers aggressiveness in altering the processing of conspecifics’ cues. We thus provide strong evidence that aggression is a consequence, not a cause, of dispersal in spiderlings. Overall, this study highlights the need of extended social interactions to preserve tolerance, which opens new perspectives for understanding the routes to permanent sociality.
Highlights
Natal dispersal is a fundamental life-history trait with profound consequences on both individual fitness and population dynamics [1]
Spiderlings that were maintained in isolation displayed more aggressive interactions than spiders raised in groups (Fig 4B, S1 Movie) (Kruskal–Wallis test: W3 = 54.28, P < 0.001). All these results indicated that social isolation triggered the onset of aggressiveness and that the rate of cannibalism gradually increased with time spent alone
The duration of the gregarious phase is a highly plastic trait that notably depends on food availability: a high density of prey typically delays the onset of dispersal and reduces the level of aggression [25, 26, 33, 34, 43]
Summary
Natal dispersal is a fundamental life-history trait with profound consequences on both individual fitness and population dynamics [1]. In many taxa of invertebrates and vertebrates, the females lay a clutch of eggs, and after hatching, the offspring display a transient phase of aggregation [2,3,4,5,6,7,8]. The shift from group to solitary living during ontogeny implies that the advantages of gregariousness are outweighed by the costs, which can result, for instance, from. In transient group-living species, natal dispersal is concomitant with the dissolution of the aggregate
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