Kin selection theory suggests that altruistic behaviors can increase the fitness of altruists when recipients are genetic relatives. Although selection can favor the ability of organisms to preferentially cooperate with close kin, indiscriminately helping all group mates may yield comparable fitness returns if relatedness within groups is very high. Here, we show that meerkats (Suricata suricatta) are largely indiscriminate altruists who do not alter the amount of help provided to pups or group mates in response to their relatedness to them. We present a model showing that indiscriminate altruism may yield greater fitness payoffs than kin discrimination where most group members are close relatives and errors occur in the estimation of relatedness. The presence of errors in the estimation of relatedness provides a feasible explanation for associations between kin discriminative helping and group relatedness in eusocial and cooperatively breeding animals.

One important but understudied way in which climate change may impact the fitness of individuals and populations is by altering the prevalence of infectious disease outbreaks. This is especially true in social species where endemic diseases are widespread. Here we use 22 years of demographic data from wild meerkats (Suricata suricatta) in the Kalahari, where temperatures have risen steadily, to project group persistence under interactions between weather extremes and fatal tuberculosis outbreaks caused by infection with Mycobacterium suricattae. We show that higher temperature extremes increase the risk of outbreaks within groups by increasing physiological stress as well as the dispersal of males, which are important carriers of tuberculosis. Explicitly accounting for negative effects of tuberculosis outbreaks on survival and reproduction in groups more than doubles group extinction risk in 12 years under projected temperature increases. Synergistic climate-disease effects on demographic rates may therefore rapidly intensify climate-change impacts in natural populations.

equivalent fitness pay-offs and are triggered stochastically, selection probably favours flexibility rather than strategies that commit individuals to a specific route.

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Researchers studying mammals have frequently interpreted earlier or faster rates of ageing in males as resulting from polygyny and the associated higher costs of reproductive competition. Yet, few studies conducted on wild populations have compared sex‐specific senescence trajectories outside of polygynous species, making it difficult to make generalized inferences on the role of reproductive competition in driving senescence, particularly when other differences between males and females might also contribute to sex‐specific changes in performance across lifespan. Here, we examine age‐related variation in body mass, reproductive output and survival in dominant male and female meerkats, Suricata suricatta. Meerkats are socially monogamous cooperative breeders where a single dominant pair virtually monopolizes reproduction in each group and subordinate group members help to rear offspring produced by breeders. In contrast to many polygynous societies, we find that neither the onset nor the rate of senescence in body mass or reproductive output shows clear differences between males and females. Both sexes also display similar patterns of age‐related survival across lifespan, but unlike most wild vertebrates, survival senescence (increases in annual mortality with rising age) was absent in dominants of both sexes, and as a result, the fitness costs of senescence were entirely attributable to declines in reproductive output from mid‐ to late‐life. We suggest that the potential for intrasexual competition to increase rates of senescence in females—who are hormonally masculinized and frequently aggressive—is offset by their ability to maintain longer tenures of dominance than males, and that these processes when combined lead to similar patterns of senescence in both sexes. Our results stress the need to consider the form and intensity of sexual competition as well as other sex‐specific features of life history when investigating the operation of senescence in wild populations.

2The phenotype of parents can have long-lasting effects on the development of offspring 2 3 as well as on their behaviour, physiology, and morphology as adults. In some cases, 2 4 these changes may increase offspring fitness but, in others, they can elevate parental 2 5 fitness at a cost to the fitness of their offspring. We show that in Kalahari meerkats 2 6 (Suricata suricatta), the circulating glucocorticoid (GC) hormones of pregnant females 2 7 affect the growth and cooperative behaviour of their offspring. We performed a 3-year 2 8 experiment in wild meerkats to test the hypothesis that GC-mediated maternal effects 2 9 reduce the potential for offspring to reproduce directly and therefore cause them to 3 0 exhibit more cooperative behaviour. Daughters (but not sons) born to mothers treated 3 1 with cortisol during pregnancy were smaller early in life and exhibited significantly more 3 2 of two types of cooperative behaviour (pup rearing and feeding) once they were adults 3 3 compared to offspring from control mothers. They also had lower measures of GCs as 3 4 they aged, which could explain the observed increases in cooperative behaviour. 3 5 Because early growth is a crucial determinant of fitness in female meerkats, our results 3 6 indicate that GC-mediated maternal effects may reduce the fitness of offspring, but may 3 7 elevate parental fitness as a consequence of increasing the cooperative behaviour of 3 8 their daughters. 3 9 4 0

One contribution of 18 to a theme issue 'Developing differences: early-life effects and evolutionary medicine'.