Within-family parent-offspring co-adaptation in a wild bird: on static traits, behavioural reaction norms and sex differences

Parental care, a central component of reproduction in a wide range of animal species, often involves elaborate behavioural interactions between parents and their offspring. Due to the reciprocal nature of these interactions, it has been hypothesized that parental and offspring behaviours (e.g. parental food provisioning and offspring begging) are not only target but also agent of selection. These traits are therefore expected to co-evolve, ultimately leading to co-adaptation of parent and offspring behaviours within families. However, empirical data on such parent-offspring co-adaptation are limited, particularly for wild populations. Furthermore, mean levels of behaviour (as measured in previous studies) may not adequately describe the dynamic nature of the reciprocal interplay between parents and their offspring, and instead rather the behavioural reaction norms for provisioning and begging may be co-adapted. We applied a large-scale cross-fostering study over 3 consecutive breeding s...