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.

Collective behaviours, such as flocking in birds or decision making by bee colonies, are some of the most intriguing behavioural phenomena in the animal kingdom. The study of collective behaviour focuses on the interactions between individuals within groups, which typically occur over close ranges and short timescales, and how these interactions drive larger scale properties such as group size, information transfer within groups and group-level decision making. To date, however, most studies have focused on snapshots, typically studying collective behaviour over short timescales up to minutes or hours. However, being a biological trait, much longer timescales are important in animal collective behaviour, particularly how individuals change over their lifetime (the domain of developmental biology) and how individuals change from one generation to the next (the domain of evolutionary biology). Here, we give an overview of collective behaviour across timescales from the short to the long, illustrating how a full understanding of this behaviour in animals requires much more research attention on its developmental and evolutionary biology. Our review forms the prologue of this special issue, which addresses and pushes forward understanding the development and evolution of collective behaviour, encouraging a new direction for collective behaviour research. This article is part of a discussion meeting issue 'Collective behaviour through time'.

Finding universal rules that predict the success of potential invaders is difficult given the breadth of interactions that occur between the invader and the other species in its new range. Among animal species, behavioural traits may play an especially relevant role in mediating these interactions. Whereas the predatory behaviour of invasive predators is especially well documented, less is known about how behaviour may mediate the success of invasive prey species. Here we tested how the behaviour of both an invasive prey species, the amphipod Dikerogammarus villosus, and a common fish predator, the European perch, Perca fluviatilis, affect the outcome of predation events. Invasive D. villosus exhibited significantly greater sheltering and less exploratory behaviour than a naturalized amphipod Gammarus roeseli. This increased sheltering behaviour in the invasive amphipod appears to have a major functional consequence as this species was far less likely than the naturalized amphipod to be predated by the perch. Contrary to our predictions, the behaviour of the individual perch had no influence on consumption of either amphipod species, suggesting that amphipod behaviour was the key determinant of the success of a predation event. Our results highlight the importance of prey behaviour during predation events and emphasize that consideration of antipredator behaviour in potentially invasive prey species may help improve predictions of invasion success.

Understanding the mechanisms responsible for consistent individual differences in behaviour is a recent challenge for behavioural ecology. Although theory is rapidly developing in this area, there are few empirical tests. There are at least two hypotheses to explain why individuals behave differently from one another in a dynamic social environment. The social niche specialization hypothesis proposes that repeated social interactions generate consistent individual differences in social behaviour. The behavioural type hypothesis proposes that an individual's social behaviour reflects its behavioural type. We tested these two hypotheses by manipulating the opportunity for repeated social interactions in groups of three spine stickleback, Gasterosteus aculeatus, and by measuring the behavioural types of the same individuals in three contexts: when in a novel environment, when presented with an opportunity to associate with conspecifics and when confronted by an intruder. We found no evidence that repeated social interactions increased between-individual variation in social foraging behaviour. Instead, individuals' social foraging behaviour was related to their behavioural type, specifically their shoaling behaviour. In addition, the behavioural types of the members of a group strongly influenced a group's average foraging behaviour. Together, these results do not support the hypothesis that social dynamics within groups generates individual differences in behaviour. Instead, they suggest the reverse: individual differences in behaviour drive group-level dynamics.

Across a wide range of animal taxa, winners of previous fights are more likely to keep winning future contests, just as losers are more likely to keep losing. At present, such winner and loser effects are considered to be fairly transient. However, repeated experiences with winning and/or losing might increase the persistence of these effects, generating long-lasting consequences for social structure. To test this, we exposed genetically identical individuals of a clonal fish, the Amazon molly (Poecilia formosa), to repeated winning and/or losing dominance interactions during the first two months of their life. We subsequently investigated whether these experiences affected the fish's ability to achieve dominance in a hierarchy five months later after sexual maturity, a major life-history transition. Individuals that had only winning interactions early in life consistently ranked at the top of the hierarchy. Interestingly, individuals with only losing experience tended to achieve the middle dominance rank, whereas individuals with both winning and losing experiences generally ended up at the bottom of the hierarchy. In addition to demonstrating that early social interactions can have dramatic and long-lasting consequences for adult social behaviour and social structure, our work also shows that higher cumulative winning experience early in life can counterintuitively give rise to lower social rank later in life.

While there are now a number of theoretical models predicting how consistent individual differences in behaviour may be generated and maintained, so far, there are few empirical tests. The social niche specialization hypothesis predicts that repeated social interactions among individuals may generate among-individual differences and reinforce within-individual consistency through positive feedback mechanisms. Here, we test this hypothesis using groups of the social spider Stegodyphus mimosarum that differ in their level of familiarity. In support of the social niche specialization hypothesis, individuals in groups of spiders that were more familiar with each other showed greater repeatable among-individual variation in behaviour. Additionally, individuals that were more familiar with each other exhibited lower within-individual variation in behaviour, providing one of the first examples of how the social environment can influence behavioural consistency. Our study demonstrates the potential for the social environment to generate and reinforce consistent individual differences in behaviour and provides a potentially general mechanism to explain this type of behavioural variation in animals with stable social groups.

Behavioural individuality is thought to be caused by differences in genes and/or environmental conditions. Therefore, if these sources of variation are removed, individuals are predicted to develop similar phenotypes lacking repeatable individual variation. Moreover, even among genetically identical individuals, direct social interactions are predicted to be a powerful factor shaping the development of individuality. We use tightly controlled ontogenetic experiments with clonal fish, the Amazon molly (Poecilia formosa), to test whether near-identical rearing conditions and lack of social contact dampen individuality. In sharp contrast to our predictions, we find that (i) substantial individual variation in behaviour emerges among genetically identical individuals isolated directly after birth into highly standardized environments and (ii) increasing levels of social experience during ontogeny do not affect levels of individual behavioural variation. In contrast to the current research paradigm, which focuses on genes and/or environmental drivers, our findings suggest that individuality might be an inevitable and potentially unpredictable outcome of development.

Research focusing on among-individual differences in behaviour ('animal personality') has been blooming for over a decade. Central theories explaining the maintenance of such behavioural variation posits that individuals expressing greater "risky" behaviours should suffer higher mortality. Here, for the first time, we synthesize the existing empirical evidence for this key prediction. Our results did not support this prediction as there was no directional relationship between riskier behaviour and greater mortality; however there was a significant absolute relationship between behaviour and survival. In total, behaviour explained a significant, but small, portion (5.8%) of the variance in survival. We also found that risky (vs. "shy") behavioural types live significantly longer in the wild, but not in the laboratory. This suggests that individuals expressing risky behaviours might be of overall higher quality but the lack of predation pressure and resource restrictions mask this effect in laboratory environments. Our work demonstrates that individual differences in behaviour explain important differences in survival but not in the direction predicted by theory. Importantly, this suggests that models predicting behaviour to be a mediator of reproduction-survival trade-offs may need revision and/or empiricists may need to reconsider their proxies of risky behaviours when testing such theory.

Sex differences in the genetic architecture of behavioral traits can offer critical insight into the processes of sex-specific selection and sexual conflict dynamics. Here, we assess genetic variances and cross-sex genetic correlations of two personality traits, aggression and activity, in a sexually size-dimorphic spider, Nuctenea umbratica. Using a quantitative genetic approach, we show that both traits are heritable. Males have higher heritability estimates for aggressiveness compared to females, whereas the coefficient of additive genetic variation and evolvability did not differ between the sexes. Furthermore, we found sex differences in the coefficient of residual variance in aggressiveness with females exhibiting higher estimates. In contrast, the quantitative genetic estimates for activity suggest no significant differentiation between males and females. We interpret these results with caution as the estimates of additive genetic variances may be inflated by nonadditive genetic effects. The mean cross-sex genetic correlations for aggression and activity were 0.5 and 0.6, respectively. Nonetheless, credible intervals of both estimates were broad, implying high uncertainty for these estimates. Future work using larger sample sizes would be needed to draw firmer conclusions on how sexual selection shapes sex differences in the genetic architecture of behavioral traits.

The social niche specialization hypothesis predicts that animal personalities emerge as a result of individuals occupying different social niches within a group. Here we track individual personality and performance and collective performance among groups of social spiders where we manipulated the familiarity of the group members. We show that individual personalities, as measured by consistent individual differences in boldness behavior, strengthen with increasing familiarity and that these personalities can be disrupted by a change in group membership. Changing group membership negatively impacted both individual and group performance. Individuals in less familiar groups lost weight, and these groups were less successful at performing vital collective tasks. These results provide a mechanism for the evolution of stable social groups by demonstrating that social niche reestablishment carries a steep cost for both individuals and groups. Social niche specialization may therefore provide a potential first step on the path toward more organized social systems.