Integrated phenotypes, that is, correlated suites of traits, can impact both evolutionary and ecological processes. Similarly, phenotypic plasticity, or the ability of one genotype to generate multiple phenotypes, can act as both a facilitator and constraint on evolutionary processes. While there has been an increasing focus on correlated behavioural means (i.e. behavioural syndromes), less attention has been paid to how plasticity in different behavioural traits may be correlated. Such correlated behavioural plasticities are likely to affect evolution and ecology, although possibly in different ways. Here, we review key insights from three research fields, behavioural syndromes, phenotypic plasticity and integrated phenotypes to provide a conceptual framework to understand why, how and when plasticities of different behavioural traits may become correlated. In particular, the conditions under which plasticity and behavioural syndromes are predicted to be important are also where correlated behavioural plasticities are likely to have the strongest impacts. In this review, we define correlated behavioural plasticities, summarize the conditions that are likely to give rise to them and highlight testable predictions in an effort to spark targeted research into this important phenomenon. We also provide a worked example to highlight how studying correlated plasticity can yield important new insights.

Populations of independently oscillating agents can sometimes synchronize. In the context of animal societies, conspicuous synchronization of activity is known in some social insects. However, the causes of variation in synchrony within and between species have received little attention. We repeatedly assessed the short-term activity cycle of ant colonies (Temnothorax rugatulus) and monitored the movements of individual workers and queens within nests. We detected persistent differences between colonies in the waveform properties of their collective activity oscillations, with some colonies consistently oscillating much more erratically than others. We further demonstrate that colony crowding reduces the rhythmicity (i.e., the consistent timing) of oscillations. Workers in both erratic and rhythmic colonies spend less time active than completely isolated workers, but workers in erratic colonies oscillate out of phase with one another. We further show that the queen's absence can impair the ability of colonies to synchronize worker activity and that behavioral differences between queens are linked with the waveform properties of their societies.

The physical environment occupied by group-living animals can profoundly affect their cooperative social interactions and therefore their collective behavior and success. These effects can be especially apparent in human-modified habitats, which often harbor substantial variation in the physical environments available within them. For nest-building animal societies, this influence of the physical environment on collective behavior can be mediated by the construction of nests-nests could either buffer animal behavior from changes in the physical environment or facilitate shifts in behavior through changes in nest structure. We test these alternative hypotheses by examining the differences in collective prey-attacking behavior and colony persistence between fence-dwelling and tree-dwelling colonies of Stegodyphus dumicola social spiders. Fences and trees represent substantially different physical environments: fences are 2-dimensional and relatively homogenous environments, whereas tree branches are 3-dimensional and relatively heterogeneous. We found that fence-dwelling colonies attack prey more quickly and with more attackers than tree-dwelling colonies in both field and controlled settings. Moreover, in the field, fence-dwelling colonies captured more prey, were more likely to persist, and had a greater number of individuals remaining at the end of the experiment than tree-dwelling colonies. Intriguingly, we also observed a greater propensity for colony fragmentation in tree-dwelling colonies than fence-dwelling colonies. Our results demonstrate that the physical environment is an important influence on the collective behavior and persistence of colonies of social spiders, and suggest multiple possible proximate and ultimate mechanisms-including variation in web complexity, dispersal behavior, and bet-hedging-by which this influence may be realized.