Hormonal mediation of a carry‐over effect in a wild cooperative mammal

Summary Recent research has shown that parental investment in one breeding attempt often has a profound negative impact on the level of parental investment in subsequent breeding attempts. However, the mechanistic underpinnings that mediate such carry‐over effects are poorly understood. Here, we hypothesise that carry‐over effects arise because energetic losses lead to elevated levels of glucocorticoid ‘stress’ hormones which inhibit future investment and thereby maintain energetic homeostasis. We investigate this hypothesis through a detailed investigation of a carry‐over effect of (allo‐) parental investment in the cooperatively breeding banded mongoose ( Mungos mungo ). Using a combination of non‐invasive hormone monitoring and feeding experiments, we demonstrate (i) that high glucocorticoid concentrations prior to breeding predict reduced alloparental investment; (ii) that energetic losses associated with high alloparental investment lead to an increase in glucocorticoid concentrations during the breeding attempt; and (iii) that elevated glucocorticoid concentrations persist into a time period that is known to affect future investment, although high pup mortality meant that we could not measure effects on subsequent alloparental investment directly. Together, our results provide strong evidence for the hypothesis that carry‐over effects on parental investment are mediated by circulating glucocorticoid concentrations. Since an individual's stress physiology is shaped by early‐life and social factors, our findings may help to explain how these factors contribute to individual variation in parental investment and lifetime reproductive success.