Reversal of the fecundity / longevity trade-off across social transitions in ants

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Investigating the reversal of the fecundity/longevity trade-off in social insects will provide important insights into the modulation of senescence. So far, studies have failed to find common molecular regulators of ageing across the social insects, possibly because uncontrolled ecological variation between the typical study species has covered key factors regulating ageing. We propose to tackle this problem by using a comparative approach focussed on ants, to identify senescence regulators that are independent of any model species' specific ecology or phylogenetic position.Theoretical work from the 1st funding phase of our research unit predicts that any reproductive potential of social insect workers should select for longer life expectancy. In most ant species, workers can produce haploid males. They usually do so when the queen dies, to gain direct fitness. However, workers typically cannot fully replace the queen because they lack the ability to produce diploid queens and workers. Interestingly, two alternative worker types have evolved repeatedly in ants: totipotent workers that can produce both males and females, and sterile workers that cannot produce any viable offspring. In addition to these physiological constraints, a worker's chance for direct reproduction also depends on colony-level life-history parameters, such as colony size and queen number, which should further affect worker ageing mechanisms.We will investigate how caste (queen or worker), fecundity (egg-laying or not), and age (young or old) affect gene expression in 15 species of ants. We carefully selected species with varying colony size and queen number, to quantify the effect of worker reproductive potential on senescence independent of the species' ecology and phylogenetic position. Two factors that prolong lives in many species are the resilience to oxidative stress and pathogen exposure. It has been proposed that social insect queens live longer because workers protect them against these environmental stressors and/or provide them with enough resources to maintain active repair and defence mechanisms for a longer time. In the proposed project, we will experimentally investigate whether ant workers with different reproductive potential (across and within 15 species) also differ in their resilience to oxidative stress and immune challenge.The workload of collecting the ants from the field and conducting the experiments in the laboratory will require the combined force and expertise of three experienced ant researchers. Overall, this comparative project across 15 ant species will provide valuable information on the molecular and physiological mechanisms underlying ageing in ants, how fecundity is linked to longevity in both queens and workers, and our general understanding of the reversal of the fecundity/longevity trade-off on the background of transitions in advanced social evolution.