Investment in offspring care commonly leads to a reduction in survival and fecundity, generating a trade-off between care of current young and future reproduction. Theory suggests that variation in this trade-off may explain the conspicuous individual differences in helping effort observed in cooperative breeders. In non-social species, testosterone is often found to mediate the trade-off between offspring care and reproduction. However, little is known about the mechanism mediating the trade-off between helping and future reproduction in cooperatively-breeding vertebrates. Here, we investigate testosterone as a candidate mechanism mediating trade-offs between cooperative offspring care and reproduction in the banded mongoose (Mungos mungo). Periods of high investment in offspring care are preceded by low faecal testosterone metabolite (fT) concentrations, suggesting that testosterone may inhibit offspring care in this species. During group oestrous, high ranking individuals with access to mates show elevated fT concentrations and a concurrent decrease in offspring care investment. However, outside of group oestrous, when there are no available mating opportunities, we find no correlations between individual rank and fT concentrations or investment in offspring care. These results provide evidence for testosterone mediation of the trade-off between offspring care and current reproduction in the banded mongoose, similar to that seen in non-social species. However, the mechanism mediating the trade-off between offspring care and future reproduction remains unknown. Together, these results highlight understanding the role of physiological mechanisms in mediating behavioural trade-offs as a key area of study to explain within-group variation in cooperative investment.
Individual differences in cooperative investment can be consistent and persist after life-history variation has been controlled for. This suggests that plasticity of cooperative behaviours may be limited, and individuals may be constrained to different behavioural trajectories or behavioural roles within animal societies. We use long-term observations of cooperative offspring care and mate-guarding behaviours in a wild population of banded mongooses (Mungos mungo) to investigate lifetime patterns of behavioural consistency in a social context. Moreover, we examine patterns of consistent individual differences through time and across contexts to investigate what selection pressures may be driving consistent individual differences in this system. We find evidence for consistent individual differences in both cooperative and competitive behaviours, though the patterns of consistency are different for each behaviour. We suggest that changes in the costs of offspring care and the availability of mates that occur through time may drive variation in behavioural consistency seen between different age ranks. Individual differences in two forms of pup care are correlated, suggesting that individuals are not specialised to different cooperative activities, rather they may be specialised as helpful and selfish individuals. We find no evidence of correlation between individual differences in investment in offspring care and mate-guarding behaviours, suggesting that individuals do not show life time specialisations to roles as carers and breeders. This is one of the first studies to test lifetime consistency of behaviours in the wild, and may be the first to investigate consistencies in cooperative and competitive behaviours concurrently. Evidence for lifetime consistency of individual differences is suggestive of lifetime behavioural trajectories and advocates further study into early-life effects to determine the factors that lead to different individual trajectories.