Intralocus sexual conflict (IaSC) is pervasive because males and females experience differences in selection but

Males and females have different routes to successful reproduction, resulting in sex differences in lifespan and age-specific allocation of reproductive effort. The trade-off between current and future reproduction is often resolved differently by males and females, and both sexes can be constrained in their ability to reach their sex-specific optima owing to intralocus sexual conflict. Such genetic antagonism may have profound implications for evolution, but its role in ageing and lifespan remains unresolved. We provide direct experimental evidence that males live longer and females live shorter than necessary to maximize their relative fitness in Callosobruchus maculatus seed beetles. Using artificial selection in a genetically heterogeneous population, we created replicate long-life lines where males lived on average 27 per cent longer than in short-life lines. As predicted by theory, subsequent assays revealed that upward selection on male lifespan decreased relative male fitness but increased relative female fitness compared with downward selection. Thus, we demonstrate that lifespan-extending genes can help one sex while harming the other. Our results show that sexual antagonism constrains adaptive life-history evolution, support a novel way of maintaining genetic variation for lifespan and argue for better integration of sex effects into applied research programmes aimed at lifespan extension.

Summary1. Sentinel behaviour involves a unique cooperative system of dedicated look-outs which protect members of their social group from attack by predators. Using detailed observations from groups of Arabian babblers, Turdoides squamiceps , we tested the original theoretical suggestion that cooperative sentinel systems are simply the result of individually selfish state-dependent patterns of behaviour. 2. Sentinel effort and the number of sentinel bouts per individual per hour were greater for males than females, and both increased with individual dominance status within the group. 3. Sentinel behaviour was unaffected by group social structure, in terms of patterns of relatedness and the number of potential breeders. 4. Total group sentinel effort increased with group size, while the effort per individual decreased irrespective of sex and dominance rank. Simultaneous sentinel behaviour by two or more birds was very rare, but increased with group size. 5. Sentinel effort followed seasonal fluctuations in food availability, but not peaks of raptor migration through the study site. 6. Body mass was greater for males than females and was positively related to dominance rank. Overall, body mass explained much of the variation in individual sentinel effort both within and between birds. However, data on individual foraging performance could not be related to changes in body mass and thus to differences in sentinel effort. 7. Sentinel behaviour in groups of Arabian babblers therefore confirms many of the predictions arising from state-dependent models of cooperative, yet individually selfish, sentinel behaviour.