Social isolation increases male aggression toward females in the field cricket Gryllus bimaculatus

Isolation disrupts social interactions and destabilizes brain development in bumblebees

Social isolation, particularly in early life, leads to deleterious physiological and behavioral outcomes. Here, we leverage new high-throughput tools to comprehensively investigate the impact of isolation in the bumblebee, Bombus impatiens, from behavioral, molecular, and neuroanatomical perspectives. We reared newly emerged bumblebees in complete isolation, in small groups, or in their natal colony, and then analyzed their behaviors while alone or paired with another bee. We find that when alone, individuals of each rearing condition show distinct behavioral signatures. When paired with a conspecific, bees reared in small groups or in the natal colony express similar behavioral profiles. Isolated bees, however, showed increased social interactions. To identify the neurobiological correlates of these differences, we quantified brain gene expression and measured the volumes of key brain regions for a subset of individuals from each rearing condition. Overall, we find that isolation increases social interactions and disrupts gene expression and brain development. Limited social experience in small groups is sufficient to preserve typical patterns of brain development and social behavior.

Social isolation impairs feed intake, growth and behavioural patterns of catfish under culture conditions

Globally, the culture of fishes is important for food production. There is a growing interest in understanding and improving the welfare of cultured fish from both ethical and production perspectives. Social isolation is a common practice in catfish farming. This study assessed how social interactions affect the feeding behaviour, growth performance, and behavioural pattern of Clarias gariepinus under different social conditions. Juveniles of African catfish with a mean weight of 23.6 ± 1.09 g were stocked in 20L-aquaria (1.7 m × 1.2 m × 1.0 m) and fed twice daily in isolated (one fish/tank; N = 6 replicates) and non-isolated (six fish/tank; N = 6 replicates) conditions for a 36-day experimental period. Feed intake and growth response were monitored, while behavioural patterns were observed twice per week using focal sampling techniques for a total of 40 minutes per day. Wilcoxon two-sample tests and GLMs were used to analyse the data. Social context significantly (P < 0.001) affected the feed intake, feeding duration, and other observed behavioural patterns. However, the time of feeding (P > 0.001) did not affect the feed intake or the duration of feeding. Fish cultured in non-isolated conditions consumed more pellets (63 ± 2.36). The duration of feeding was longer in isolated conditions (431 s) while the latency to feed increased significantly (P < 0.001) from the first and fifth day of the experiment for the non-isolated and isolated, respectively. Behaviourally, isolated groups were inactive (W_s = 446.34, z = 5.397; P < 0.01) and displayed fewer aggressive acts (W_s = 0.95, z = 1.19; P < 0.01), while non-isolated groups were more active (W_s = 564.39, z = -5.397; P < 0.01) and displayed more escape attempts (W_s = 11.56, z =  -5.47; P < 0.01). Non-isolated groups had higher (W_s = 23.41, z = 1.06; P < 0.01) number of scars and bruises. Furthermore, non-isolated fish had a higher specific growth rate (2.36 ± 0.12), feed conversion ratio (1.27 ± 0.01) and a better condition factor (1.01 ± 0.08). Conclusively, these findings are relevant to African catfish welfare as social isolation changes the behavioural attributes, feeding pattern and growth rate of C. gariepinus. However, social context should be monitored since it resulted in more scars and bruises, which might affect the acceptability and welfare of this aquatic fish species.

Social isolation interaction with the feeding regime differentially affects survival and results in a hump-shaped pattern in movement activity

Eusocial insects depend on their colonies, and it is therefore clear why isolation triggers many negative effects on isolated individuals. Here, we examined the effect of social isolation on the desert ant Cataglyphis niger, asking whether isolation, either with access to food or under starvation, impairs survival, and whether isolation modifies movement activity and digging to bypass an obstacle. Social isolation led to shorter survival but only when food was provided. This effect might be due to food not being digested correctly under isolation. Although isolated ant workers were more active immediately post isolation than 2-24 hours later, their movement moderately increased two days post isolation. We suggest that the changes in movement activity are adaptive: first, the worker increases activity intended to reunite it with the lost colony. Then, when the colony is not found, it reduces activity to conserve energy. It later increases activity as a final attempt to detect the colony. We expected isolated workers to dig faster to bypass an obstacle, but we did not detect any effect on digging behavior. We demonstrate here the complex effects of isolation on survival and movement activity, in interaction with additional factors - feeding and isolation duration.

Social intolerance is a consequence, not a cause, of dispersal in spiders

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.

Behavioral experiments with the spider Agelena labyrinthica, coupled to computational modelling, show that an increase in mobility with age drives dispersal in gregarious spiderlings of a solitary species and that the subsequent social isolation triggers aggression.

Early social isolation impairs development, mate choice and grouping behaviour of predatory mites

The social environment early in life is a key determinant of developmental, physiological and behavioural trajectories across vertebrate and invertebrate animals. One crucial variable is the presence/absence of conspecifics. For animals usually reared in groups, social isolation after birth or hatching can be a highly stressful circumstance, with potentially long-lasting consequences. Here, we assessed the effects of social deprivation (isolation) early in life, that is, absence of conspecifics, versus social enrichment, that is, presence of conspecifics, on developmental time, body size at maturity, mating behaviour and group-living in the plant-inhabiting predatory mite Phytoseiulus persimilis. Socially deprived protonymphs developed more slowly and were less socially competent in grouping behaviour than socially enriched protonymphs. Compromised social competence in grouping behaviour was evident in decreased activity, fewer mutual encounters and larger interindividual distances, all of which may entail severe fitness costs. In female choice/male competition, socially deprived males mated earlier than socially enriched males; in male choice/female competition, socially deprived females were more likely to mate than socially enriched females. In neither mate choice situation did mating duration or body size at maturity differ between socially deprived and enriched mating opponents. Social isolation-induced shifts in mating behaviour may be interpreted as increased attractiveness or competitiveness or, more likely, as hastiness and reduced ability to assess mate quality. Overall, many of the social isolation-induced behavioural changes in P. persimilis are analogous to those observed in other animals such as cockroaches, fruit flies, fishes or rodents. We argue that, due to their profound and persistent effects, early social deprivation or enrichment may be important determinants in shaping animal personalities.