The exceptional longevity of social insect queens despite their lifelong high fecundity remains poorly understood in ageing biology. To gain insights into the mechanisms that might underlie ageing in social insects, we compared gene expression patterns between young and old castes (both queens and workers) across different lineages of social insects (two termite, two bee and two ant species). After global analyses, we paid particular attention to genes of the insulin/insulin-like growth factor 1 signalling (IIS)/target of rapamycin (TOR)/juvenile hormone (JH) network, which is well known to regulate lifespan and the trade-off between reproduction and somatic maintenance in solitary insects. Our results reveal a major role of the downstream components and target genes of this network (e.g. JH signalling, vitellogenins, major royal jelly proteins and immune genes) in affecting ageing and the caste-specific physiology of social insects, but an apparently lesser role of the upstream IIS/TOR signalling components. Together with a growing appreciation of the importance of such downstream targets, this leads us to propose the TI–J–LiFe ( T OR/ I IS– J H– Li fespan and Fe cundity) network as a conceptual framework for understanding the mechanisms of ageing and fecundity in social insects and beyond. This article is part of the theme issue ‘Ageing and sociality: why, when and how does sociality change ageing patterns?’

Longevity is traded off with fecundity in most solitary species, but the two traits are positively linked in social insects. In ants, the most fecund individuals (queens and kings) live longer than the non-reproductive individuals, the workers. In many species, workers may become fertile following queen loss, and recent evidence suggests that worker fecundity extends worker lifespan. We postulated that this effect is in part owing to improved resilience to oxidative stress, and tested this hypothesis in three Myrmicine ants: Temnothorax rugatulus, and the leaf-cutting ants Atta colombica and Acromyrmex echinatior . We removed the queen from colonies to induce worker reproduction and subjected workers to oxidative stress. Oxidative stress drastically reduced survival, but this effect was less pronounced in leaf-cutting ant workers from queenless nests. We also found that, irrespective of oxidative stress, outside workers died earlier than inside workers did, likely because they were older. Since At. colombica workers cannot produce fertile offspring, our results indicate that direct reproduction is not necessary to extend the lives of queenless workers. Our findings suggest that workers are less resilient to oxidative stress in the presence of the queen, and raise questions on the proximate and ultimate mechanisms underlying socially mediated variation in worker lifespan. This article is part of the theme issue ‘Ageing and sociality: why, when and how does sociality change ageing patterns?’

Division of labor (DOL) is a characteristic trait of insect societies, where tasks are generally performed by groups of specialized individuals. In social insects, young workers perform duties within the safety of the nest (e.g., brood care), while older ones undertake riskier tasks (e.g., foraging for food). This DOL remains dynamic, and workers may switch back and forth when colony needs require. Theoretical models propose that workers differ in their thresholds to take on certain tasks when confronted to task-related stimuli, resulting in variation in their response to such stimuli, task-specialization, and thus DOL. Such models assume that workers differ in how they respond to task-related information rather than in how they perceive such information. Here, we test the hypothesis that DOL rather stems from workers differing in their efficiency to detect task-related stimuli. We used transcriptomics to compare gene expression in the antennae and in the brain between nurses and foragers in the ant Temnothorax longispinosus. We found that seven times as many genes were differentially expressed between the behavioral phenotypes in the antennae compared to the brain. Moreover, nearly half of all odorant receptors genes were differentially expressed, with an overrepresentation of the 9-exon gene subfamily upregulated in the antennae of nurses. These findings indicate that nurses and foragers differ in how they perceive their olfactory environment, and task-related signals. The results of this study support the hypothesis that a sensory filter in the antennae predisposes workers to specialize in specific tasks, and may improve our understanding of DOL in insect societies.