How fitness consequences of early‐life conditions vary with age in a long‐lived seabird: A Bayesian multivariate analysis of age‐specific reproductive values

• Published in: The Journal of animal ecology Vol. 90; no. 6; pp. 1505 - 1514
• Main Authors: Vedder, Oscar, Pen, Ido, Bouwhuis, Sandra
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.06.2021
• Subjects: Adults; Age; ageing; Animal reproduction; antagonistic pleiotropy; Aquatic birds; Bayesian analysis; Breeding seasons; Breeding success; Costs; Empirical analysis; Fitness; Hatching; hatching asynchrony; hatching order; Juveniles; lifetime reproductive success; Multivariate analysis; Offspring; parental effects; parent‐offspring conflict; Reproduction; Reproductive fitness; Senescence; sibling competition; Statistical analysis; Survival; hatching asynchrony; ageing; antagonistic pleiotropy; parent-offspring conflict; hatching order; lifetime reproductive success; sibling competition; parental effects
• ISSN: 0021-8790; 1365-2656
• DOI: 10.1111/1365-2656.13471

Evolutionary theory suggests that individuals can benefit from deferring the fitness cost of developing under poor conditions to later in life. Although empirical evidence for delayed fitness costs of poor developmental conditions is abundant, individuals that die prematurely have not often been incorporated when estimating fitness, such that age‐specific fitness costs, and therefore the relative importance of delayed fitness costs are actually unknown. We developed a Bayesian statistical framework to estimate age‐specific reproductive values in relation to developmental conditions. We applied it to data obtained from a long‐term longitudinal study of common terns Sterna hirundo, using sibling rank to describe variation in developmental conditions. Common terns have a maximum of three chicks, and later hatching chicks acquire less food, grow more slowly and have a lower fledging probability than their earlier hatched siblings. We estimated fitness costs in adulthood to constitute c. 45% and 70% of the total fitness costs of hatching third and second, respectively, compared to hatching first. This was due to third‐ranked hatchlings experiencing especially high pre‐fledging mortality, while second‐ranked hatchlings had lower reproductive success in adulthood. Both groups had slightly lower adult survival. There was, however, no evidence for sibling rank‐specific rates of senescence. We additionally found years with low fledgling production to be associated with particularly strong pre‐fledging selection on sibling rank, and with increased adult survival to the next breeding season. This suggests that adults reduce parental allocation to reproduction in poor years, which disproportionately impacts low‐ranked offspring. Interpreting these results, we suggest that selection at the level of the individual offspring for delaying fitness costs is counteracted by selection for parental reduction in brood size when resources are limiting. The authors partition the lifetime fitness consequences of poor early‐life conditions over age in a long‐lived seabird. Their results suggest that selection on parents may favour earlier expression of negative fitness consequences than selection on the offspring.