Eusocial Hymenoptera show a unique divergence in lifespan of queens and workers; queens belong to the longest lived insects while workers in most eusocial species have significantly shorter lives. The different phenotypes within a colony emerge through reproductive division of labour, which is a characteristic trait of eusocial animals. Division of labour as a measure of organismal complexity increases with colony size in eusocial species similar to the increase of complexity with size that has been shown for the whole range of living organisms. We show that queen and worker lifespan diverge in closely related species representing the transition from solitary to social life and show that queen and worker lifespan are correlated if colony size is taken into account: with increasing colony size the lifespan differential between queen and worker increases, whereas neither queen nor worker lifespan is associated with colony size. Additionally, the lifespan differential is better explained by colony size than by the weight differences between the castes. The divergence of phenotypes found is in line with the increasing specialization of subunits in larger organisms, which leads to increasing complexity. We argue that division of labour is acting to increase colony efficiency, which in turn shapes the investments made into individuals leading to short‐lived workers and long‐lived queens. Additionally, maintenance investments may be shaped due to the variable extrinsic risk faced by different castes. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109, 710–724.

The life-prolonging effects of antioxidants have long entered popular culture, but the scientific community still debates whether free radicals and the resulting oxidative stress negatively affect longevity. Social insects are intriguing models for analysing the relationship between oxidative stress and senescence because life histories differ vastly between long-lived reproductives and the genetically similar but short-lived workers. Here, we present the results of an experiment on the accumulation of oxidative damage to proteins, and a comparative analysis of the expression of 20 selected genes commonly involved in managing oxidative damage, across four species of social insects: a termite, two bees and an ant. Although the source of analysed tissue varied across the four species, our results suggest that oxidative stress is a significant factor in senescence and that its manifestation and antioxidant defenses differ among species, making it difficult to find general patterns. More detailed and controlled investigations on why responses to oxidative stress may differ across social species may lead to a better understanding of the relations between oxidative stress, antioxidants, social life history and senescence. This article is part of the theme issue ‘Ageing and sociality: why, when and how does sociality change ageing patterns?'

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While the extraordinary life span of queens and division of labor in eusocial societies have been well studied, it is less clear which selective forces act on the short life span of workers. The disparity of life span between the queen and the workers is linked to a basic issue in sociobiology: How are the resources in a colony allocated between colony maintenance and reproduction? Resources for somatic maintenance of the colony can either be invested into quality or quantity of workers. Here, we present a theoretical optimization model that uses a hierarchical trade-off within insect colonies and extrinsic mortality to explain how different aging phenotypes could have evolved to keep resources secure in the colony. The model points to the significance of two factors. First, any investment that would generate a longer intrinsic life span for workers is lost if the individual dies from external causes while foraging. As a consequence, risky environments favor the evolution of workers with a shorter life span. Second, shorter-lived workers require less investment than long-lived ones, allowing the colony to allocate these resources to sexual reproduction or colony growth.

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