IIn vertebrates, darker individuals are often found to be more active and willing to take risks (representing characteristics of a ‘proactive’ coping style), whereas lighter individuals are instead more cautious and less active (representing characteristics of a ‘reactive’ coping style). It is thus generally expected that melanin-based colouration and proactivity form a suite of positively integrated traits at the among-individual level. Here we use a multi-generational pedigree of free-living great tits (Parus major) to partition variation in, and the correlation between, melanin-based breast stripe (‘tie’) size and exploration behaviour (a proxy for coping style) into its among- and within-individual components. We show that both traits harbour heritable variation. Against predictions, tie size and speed of exploration were negatively correlated at the among-individual level due to the combined influences of permanent environmental and additive genetic effects. By contrast, the two traits were weakly positively correlated within individuals (i.e., individuals increasing in tie size after moult tended to become more explorative). The patterns of among-individual covariance were not caused by correlational selection as we found additive and opposite selection pressures acting on the two traits. These findings imply that testing hypotheses regarding the existence of a ‘syndrome’ at the among-individual level strictly requires variance partitioning to avoid inappropriate interpretations as the negative ‘unpartitioned’ phenotypic correlation between exploration and tie size resulted from counteracting effects of within- and among-individual correlations. Identifying sources and levels of (co)variation in phenotypic traits is thus critical to our understanding of biological patterns and evolutionary processes.

The data package contains three sets:
- file containing all the data used for the quantitative genetic analyses of exploratory behaviour and tie size of the Lauwersmeer great tit population
- pedigree file of the Lauwersmeer great tit population
- file containing the data used for the correlational selection analyses