More social species live longer, have longer generation times and longer reproductive windows

Life expectancy in ants explains variation in helpfulness regardless of phylogenetic relatedness

Rescue behavior aims to free a relative from danger. Ants are particularly known for such helpfulness and, perhaps not coincidentally, also show the highest level of social organization in the animal kingdom, i.e. eusociality. However, even among social species such as ants, there is a huge variation in rescue proneness, and little is understood about the underlying causes of this variation. In this study, we explore the relationship between helpfulness in the form of rescue and life expectancy, focusing on 14 ant species with diverse phylogenetic backgrounds. We posit that species with longer worker life expectancies are more prone to engaging in rescue actions. To test this, we assessed worker lifespan in each species and conducted behavioral tests simulating entrapment scenarios involving a nestmate ensnared by an artificial obstacle. Observed behaviors involved contact with the nestmate, digging around it, pulling at its body parts, and biting the entrapping obstacle. Our findings reveal that species with longer worker life expectancies exhibit higher proneness to rescue endangered nestmates, irrespective of phylogenetic relatedness. Furthermore, we found no trace of a phylogenetic signal in the life expectancies or helpfulness of workers belonging to different species. The results underscore the significance of life expectancy as a key factor influencing the likelihood of rescue behavior in ants. This phenomenon warrants further investigation, given the varied physiologies, life histories, and ecologies observed among species. Nevertheless, the impact of life expectancy on behavioral patterns in social insects suggests that this parameter is likely significant across diverse taxa.

The ecology of ageing in wild societies: linking age structure and social behaviour

The age of individuals has consequences not only for their fitness and behaviour but also for the functioning of the groups they form. Because social behaviour often changes with age, population age structure is expected to shape the social organization, the social environments individuals experience and the operation of social processes within populations. Although research has explored changes in individual social behaviour with age, particularly in controlled settings, there is limited understanding of how age structure governs sociality in wild populations. Here, we synthesize previous research into age-related effects on social processes in natural populations, and discuss the links between age structure, sociality and ecology, specifically focusing on how population age structure might influence social structure and functioning. We highlight the potential for using empirical data from natural populations in combination with social network approaches to uncover pathways linking individual social ageing, population age structure and societal functioning. We discuss the broader implications of these insights for understanding the social impacts of anthropogenic effects on animal population demography and for building a deeper understanding of societal ageing in general.This article is part of the discussion meeting issue 'Understanding age and society using natural populations'.

Ageing effects of social environments in 'non-social' insects

It is increasingly clear that social environments have profound impacts on the life histories of 'non-social' animals. However, it is not yet well known how species with varying degrees of sociality respond to different social contexts and whether such effects are sex-specific. To survey the extent to which social environments specifically affect lifespan and ageing in non-social species, we performed a systematic literature review, focusing on invertebrates but excluding eusocial insects. We found 80 studies in which lifespan or ageing parameters were measured in relation to changes in same-sex or opposite-sex exposure, group size or cues thereof. Most of the studies focused on manipulations of adults, often reporting sex differences in lifespan following exposure to the opposite sex. Some studies highlighted the impacts of developmental environments or social partner age on lifespan. Several studies explored potential underlying mechanisms, emphasizing that studies on insects could provide excellent opportunities to interrogate the basis of social effects on ageing. We discuss what these studies can tell us about the social environment as a stressor, or trade-offs in resources prompted by different social contexts. We suggest fruitful avenues for further research of social effects across a wider and more diverse range of taxa.This article is part of the discussion meeting issue 'Understanding age and society using natural populations'.

Understanding age and society using natural populations

Ageing affects almost all aspects of life and therefore is an important process across societies, human and non-human animal alike. This article introduces new research exploring the complex interplay between individual-level ageing and demography, and the consequences this interplay holds for the structure and functioning of societies across various natural populations. We discuss how this Special Issue provides a foundation for integrating perspectives from evolutionary biology, behavioural ecology and demography to provide new insights into how ageing shapes individuals' social behaviour and social associations, and how this in turn impacts social networks, social processes (such as disease or information transfer) and fitness. Through examining these topics across taxa, from invertebrates to birds and mammals, we outline how contemporary studies are using natural populations to advance our understanding of the relationship between age and society in innovative ways. We highlight key emerging research themes from this Special Issue, such as how sociality affects lifespan and health, the genetic and ecological underpinnings of social ageing and the adaptive strategies employed by different species. We conclude that this Special Issue underscores the importance of studying social ageing using diverse systems and interdisciplinary approaches for advancing evolutionary and ecological insights into both ageing and sociality more generally.This article is part of the discussion meeting issue 'Understanding age and society using natural populations '.