Evolutionary causes and consequences of consistent individual variation in cooperative behaviour

Behaviour is typically regarded as among the most flexible of animal phenotypic traits. In particular, expression of cooperative behaviour is often assumed to be conditional upon the behaviours of others. This flexibility is a key component of many hypothesized mechanisms favouring the evolution of cooperative behaviour. However, evidence shows that cooperative behaviours are often less flexible than expected and that, in many species, individuals show consistent differences in the amount and type of cooperative and non-cooperative behaviours displayed. This phenomenon is known as ‘animal personality’ or a ‘behavioural syndrome’. Animal personality is evolutionarily relevant, as it typically shows heritable variation and can entail fitness consequences, and hence, is subject to evolutionary change. Here, we review the empirical evidence for individual variation in cooperative behaviour across taxa, we examine the evolutionary processes that have been invoked to explain the existence of individual variation in cooperative behaviour and we discuss the consequences of consistent individual differences on the evolutionary stability of cooperation. We highlight that consistent individual variation in cooperativeness can both stabilize or disrupt cooperation in populations. We conclude that recognizing the existence of consistent individual differences in cooperativeness is essential for an understanding of the evolution and prevalence of cooperation.     

The role of common ancestry and gene flow in the evolution of human‐directed play behaviour in dogs

Among‐population variance of phenotypic traits is of high relevance for understanding evolutionary mechanisms that operate in relatively short timescales, but various sources of nonindependence, such as common ancestry and gene flow, can hamper the interpretations. In this comparative analysis of 138 dog breeds, we demonstrate how such confounders can independently shape the evolution of a behavioural trait (human‐directed play behaviour from the Dog Mentality Assessment project). We combined information on genetic relatedness and haplotype sharing to reflect common ancestry and gene flow, respectively, and entered these into a phylogenetic mixed model to partition the among‐breed variance of human‐directed play behaviour while also accounting for within‐breed variance. We found that 75% of the among‐breed variance was explained by overall genetic relatedness among breeds, whereas 15% could be attributed to haplotype sharing that arises from gene flow. Therefore, most of the differences in human‐directed play behaviour among breeds have likely been caused by constraints of common ancestry as a likely consequence of past selection regimes. On the other hand, gene flow caused by crosses among breeds has played a minor, but not negligible role. Our study serves as an example of an analytical approach that can be applied to comparative situations where the effects of shared origin and gene flow require quantification and appropriate statistical control in a within‐species/among‐population framework. Altogether, our results suggest that the evolutionary history of dog breeds has left remarkable signatures on the among‐breed variation of a behavioural phenotype.     

Phylogenetic analysis of correlation structure in stalk-eyed flies (Diasemopsis,Diopsidae)

Morphological divergence among species may be constrained by the pattern of genetic variances and covariances among traits within species. Assessing the existence of such a relationship in nature requires information on the stability of intraspecific correlation and covariance structure and the correspondence of this structure to the pattern of evolutionary divergence within a lineage. Here, we investigate these issues for nine morphological traits and 15 species of stalk-eyed flies in the genus Diasemopsis. Within-species matrices for these traits were generated from phenotypic data for all the Diasemopsis species and from genetic data for a single Diasemopsis species, D. dubia. The among-species pattern of divergence was assessed by calculating the evolutionary correlations for all pairwise combinations of the morphological traits along the phylogeny of these species. Comparisons of intraspecific matrices reveal significant similarity among all species in the phenotypic correlations matrices but not the covariance matrices. In addition, the differences in correlation structure that do exist among species are not related to their phylogenetic placement or change in the means of the traits. Comparisons of the phenotypic and phylogenetic matrices suggest a strong relationship between the pattern of evolutionary change among species and both the intraspecific correlation structure and the stability of this structure among species. The phenotypic and the phylogenetic matrices are significantly similar, and pairs of traits whose intraspecific correlations are more stable across taxa exhibit stronger coevolution on the phylogeny. These results suggest either the existence of strong constraints on the pattern of evolutionary change or a consistent pattern of correlated selection shaping both the phenotypic and phylogenetic matrices. The genetic correlation structure for D. dubia, however, does not correspond with patterns found in the phenotypic and phylogenetic data. Possible reasons for this disagreement are discussed.     

METAMODELS AND PHYLOGENETIC REPLICATION: A SYSTEMATIC APPROACH TO THE EVOLUTION OF DEVELOPMENTAL PATHWAYS

Molecular genetic analysis of phenotypic variation has revealed many examples of evolutionary change in the developmental pathways that control plant and animal morphology. A major challenge is to integrate the information from diverse organisms and traits to understand the general patterns of developmental evolution. This integration can be facilitated by evolutionary metamodels—traits that have undergone multiple independent changes in different species and whose development is controlled by well-studied regulatory pathways. The metamodel approach provides the comparative equivalent of experimental replication, allowing us to test whether the evolution of each developmental pathway follows a consistent pattern, and whether different pathways are predisposed to different modes of evolution by their intrinsic organization. A review of several metamodels suggests that the structure of developmental pathways may bias the genetic basis of phenotypic evolution, and highlights phylogenetic replication as a value-added approach that produces deeper insights into the mechanisms of evolution than single-species analyses.     

Population differences in behaviour are explained by shared within‐population trait correlations

Correlations in behavioural traits across time, situation and ecological context (i.e. ‘behavioural syndromes’ or ‘personality’) have been documented for a variety of behaviours, and in diverse taxa. Perhaps the most controversial inference from the behavioural syndromes literature is that correlated behaviour may act as an evolutionary constraint and evolutionary change in one’s behaviour may necessarily involve shifts in others. We test the two predictions of this hypothesis using comparative data from eighteen populations of the socially polymorphic spider, Anelosimus studiosus (Araneae, Theriidae). First, we ask whether geographically distant populations share a common syndrome. Second, we test whether population differences in behaviour are correlated similarly to within‐population trait correlations. Our results reveal that populations separated by as much as 36° latitude shared similar syndromes. Furthermore, population differences in behaviour were correlated in the same manner as within‐population trait correlations. That is, population divergence tended to be along the same axes as within‐population covariance. Together, these results suggest a lack of evolutionary independence in the syndrome’s constituent traits.     

What is comparable in comparative cognition?

To understand how complex, or 'advanced' various forms of cognition are, and to compare them between species for evolutionary studies, we need to understand the diversity of neural-computational mechanisms that may be involved, and to identify the genetic changes that are necessary to mediate changes in cognitive functions. The same overt cognitive capacity might be mediated by entirely different neural circuitries in different species, with a many-to-one mapping between behavioural routines, computations and their neural implementations. Comparative behavioural research needs to be complemented with a bottom-up approach in which neurobiological and molecular-genetic analyses allow pinpointing of underlying neural and genetic bases that constrain cognitive variation. Often, only very minor differences in circuitry might be needed to generate major shifts in cognitive functions and the possibility that cognitive traits arise by convergence or parallel evolution needs to be taken seriously. Hereditary variation in cognitive traits between individuals of a species might be extensive, and selection experiments on cognitive traits might be a useful avenue to explore how rapidly changes in cognitive abilities occur in the face of pertinent selection pressures.     

Assessing the Patterns of Evolution in Anuran Vocal Sexual Signals

Many animal species have evolved signalling traits to mediate various intra-specific interactions. Signals are particularly important for inter-sexual selection, where females use male signalling traits to select mates. Female preferences are therefore a major selective force in the evolution of these male signals, and these preferences can facilitate rapid changes in these traits in an evolutionary timeframe. This introduction of high levels of variation in inter-sexual signals may overshadow any phylogenetic patterns present. Such shadowing effects, however, should be dependant on the characteristics of traits (e.g. morphological, physiological and behavioural). Using male advertisement calls from 72 species of anuran amphibians, we tested the levels of phylogenetic signal present for a variety of call features in relation to trait types, and for calls as whole units using phylogenetic principal components analysis. We found that most call features displayed some level of phylogenetic autocorrelation (or signal), with traits that are dependent on morphology having much stronger phylogenetic signals than those based on behaviour. In addition, when calls were analysed as whole units, closely related species were found to be similar to each other, indicating that phylogenetic patterns had not been cancelled out by selection via female preferences. We suggest that signal functions, such as indicating male quality (e.g. mediated by body size) to potential mates, may place constraints on the amount of variation that can be introduced by female preferences. More research, particularly studies on other taxa, will be required to elucidate whether the patterns found in anurans are general across the animal kingdom.     

Can population genetic structure be predicted from life-history traits?

Population genetic structure is a key parameter in evolutionary biology. Earlier comparative studies have shown that genetic structure depends on species ecological attributes and life-history traits, but species phylogenetic relatedness had not been accounted for. Here we reevaluate the relationships between genetic structure and species traits in seed plants. Each species is characterized by a set of life-history and ecological features as well as by its geographic range size, its heterozygote deficit, and its genetic structure at nuclear and organelle markers to distinguish between pollen- and seed-mediated gene flow. We use both a conventional regression approach and a method that controls for phylogenetic relationships. Once phylogenetic conservatism and covariation among traits are taken into account, genetic structure is shown to be related with only a few synthetic traits, such as mating system for nuclear markers and seed dispersal mode or geographic range size for organelle markers. Along with other studies on invasiveness or rarity, our work illustrates the fact that predicting the fate of species across a broad taxonomic assemblage on the basis of simple traits is rarely possible, a testimony of the highly contingent nature of evolution.     

Be meek or be bold? A colony-level behavioural syndrome in ants

Consistent individual variation in animal behaviour is nearly ubiquitous and has important ecological and evolutionary implications. Additionally, suites of behavioural traits are often correlated, forming behavioural syndromes in both humans and other species. Such syndromes are often described by testing for variation in traits across commonly described dimensions (e.g. aggression and neophobia), independent of whether this variation is ecologically relevant to the focal species. Here, we use a variety of ecologically relevant behavioural traits to test for a colony-level behavioural syndrome in rock ants (Temnothorax rugatulus). Specifically, we combine field and laboratory assays to measure foraging effort, how colonies respond to different types of resources, activity level, response to threat and aggression level. We find evidence for a colony level syndrome that suggests colonies consistently differ in coping style—some are more risk-prone, whereas others are more risk-averse. Additionally, by collecting data across the North American range of this species, we show that environmental variation may affect how different populations maintain consistent variation in colony behaviour.     

The evolution of waving displays in fiddler crabs (Uca spp., Crustacea: Ocypodidae)

Male fiddler crabs are commonly recognized by the presence of a single massive claw used in a variety of contexts, including territorial defence, agonistic interactions, and courtship behaviour. The most common behavioural context involving these enlarged chelipeds is their use in waving displays, which are remarkably diverse among species. Although the waving display is one of the most obvious behavioural features of male fiddler crabs, little is known about their main evolutionary trends during the diversification of the genus. The present study employed phylogenetic comparative methods to investigate the evolution of waving behaviour in a sample of 19 species of Uca from Central and North America. Digital recordings were used to quantify the temporal dynamics of waving behaviour in each species. Multivariate ordination methods were used to assess whether different elements of the display showed distinct evolutionary dynamics, particularly with respect to body size and the environment where species are most commonly found. Most of the interspecific variation in displays involves differences in the overall waving velocity, with no correspondence to their local environments, nor their body size. Interestingly, despite the strong concentration of variance in the first two ordination axes, there was no statistically significant evidence for phylogenetic signals in their respective scores. These results suggest that the overall structure of waving displays is evolutionarily labile, at the same time as being concentrated in a few particular axes of variation, possibly indicating evolution along lines of least resistance. The approach employed in the present study highlights the utility of phylogenetic comparative methods for elucidating the evolution of complex behavioural characteristics, such as the waving display in male fiddler crabs. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 307–315.     

Interspecific competition affects evolutionary links between cavity nesting,migration and clutch size in Old World flycatchers (Muscicapdae)

The ecology of cavity nesting in passerine birds has been studied extensively, yet there are no phylogenetic comparative studies that quantify differences in life history traits between cavity‐ and open‐nesting birds within a passerine family. We test existing hypotheses regarding the evolutionary significance of cavity nesting in the Old World flycatchers (Muscicapidae). We used a multi‐locus phylogeny of 252 species to reconstruct the evolutionary history of cavity nesting and to quantify correlations between nest types and life history traits. Within a phylogenetic generalized linear model framework, we found that cavity‐nesting species are larger than open‐nesting species and that maximum clutch sizes are larger in cavity‐nesting lineages. In addition to differences in life history traits between nest types, species that breed at higher latitudes have larger average and maximum clutch sizes and begin to breed later in the year. Gains and losses of migratory behaviour have occurred far more often in cavity‐nesting lineages than in open‐nesting taxa, suggesting that cavity nesting may have played a crucial role in the evolution of migratory behaviour. These findings identify important macro‐evolutionary links between the evolution of cavity nesting, clutch size, interspecific competition and migratory behaviour in a large clade of Old World songbirds.     

The comparative method in conservation biology

The phylogenetic comparative approach is a statistical method for analyzing correlations between traits across species. Whilst it has revolutionized evolutionary biology, can it work for conservation biology? Although it is correlative, advocates of the comparative method hope that it will reveal general mechanisms in conservation, provide shortcuts for prioritizing conservation research, and enable us to predict which species will experience (or create) problems in the future. Here, we ask whether these stated management goals are being achieved. We conclude that comparative methods are stimulating research into the ecological mechanisms underlying conservation, and are providing information for preemptive screening of problem species. But comparative analyses of extinction risk to date have tended to be too broad in scope to provide shortcuts to conserving particular endangered species. Correlates of vulnerability to conservation problems are often taxon, region and threat specific, so models must be narrowly focused to be of maximum practical use.     

Effects of adoption of freshwater residency on life-history ecology of terapontid grunters

1. While fish reproduction has played a critical role in development of life-history theory, the collective effects of a marine-to-freshwater invasion on a clade's reproductive ecology have rarely been explored in a phylogenetic context. We analysed and compared a range of quantitative and qualitative components of reproductive ecology in the Australasian terapontid fishes, a family distributed widely across marine, estuarine and freshwater habitats in the Indo-Pacific region. We specifically tested hypotheses that life-history strategies such as larger egg sizes and reduced fecundities are a key characteristic of freshwater species in comparison with their close marine relatives, and also fit a range of currently available evolutionary models describing the processes of ecomorphological and macrohabitat-related diversification.
2. Using recently developed phylogenetic comparative methods, differences in several quantitative reproductive traits were evident between marine and freshwater species, with reductions in average fecundity and increases in average egg size specifically characterising freshwater species. Evolutionary modelling of major trait axes, as well as specific traits across the family, highlighted significant increases in rates of evolutionary diversification across both freshwater lineages and within freshwater subclades. Modelling also supported the evolution of distinctive morpho-ecotype optima between marine and freshwater species over simpler models of random-walk evolution or single morphological optima.
3. Review of life-history behaviour identified environmental stimuli related to photoperiod, temperature, and lunar-tidal cycles (and possibly combinations thereof) as playing an important role in stimulating spawning behaviour in most marine–euryhaline species. While some of these variables (temperature and photoperiod) continue to play an important role in some freshwater species, flow regime, particularly streamflow increases, appear more important in stimulating spawning responses, underlining the role of flow regime emerging as a master variable shaping evolutionary trajectories in freshwater clades.
4. In this review and meta-analysis, we document that adaptation to an entirely freshwater existence has catalysed significant, and in several cases, relatively rapid adaptive evolution to very different life-history strategies within freshwater species. The invasion of freshwaters has had profound impacts on the trajectory of terapontid life-history evolution, driving significant changes in a range of traits relating to fecundity, egg size, spawning stimuli, and spawning substratum. Collective results suggest a distinct adaptive landscape difference between marine and freshwaters. Terapontids can provide a useful model for assessing the consistency of these outcomes with other freshwater-invading groups.

     

A comparative analysis of dispersal syndromes in terrestrial and semi‐terrestrial animals

Dispersal, the behaviour ensuring gene flow, tends to covary with a number of morphological, ecological and behavioural traits. While species‐specific dispersal behaviours are the product of each species’ unique evolutionary history, there may be distinct interspecific patterns of covariation between dispersal and other traits (‘dispersal syndromes’) due to their shared evolutionary history or shared environments. Using dispersal, phylogeny and trait data for 15 terrestrial and semi‐terrestrial animal Orders (> 700 species), we tested for the existence and consistency of dispersal syndromes across species. At this taxonomic scale, dispersal increased linearly with body size in omnivores, but decreased above a critical length in herbivores and carnivores. Species life history and ecology significantly influenced patterns of covariation, with higher phylogenetic signal of dispersal in aerial dispersers compared with ground dwellers and stronger evidence for dispersal syndromes in aerial dispersers and ectotherms, compared with ground dwellers and endotherms. Our results highlight the complex role of dispersal in the evolution of species life‐history strategies: good dispersal ability was consistently associated with high fecundity and survival, and in aerial dispersers it was associated with early maturation. We discuss the consequences of these findings for species evolution and range shifts in response to future climate change.     

Phylogenetic convergence and multiple shell shape optima for gliding scallops (Bivalvia: Pectinidae)

An important question in evolutionary biology is how often, and to what extent, do similar ecologies elicit distantly related taxa to evolve towards the same phenotype? In some scenarios, the repeated evolution of particular phenotypes may be expected, for instance when species are exposed to common selective forces that result from strong functional demands. In bivalved scallops (Pectinidae), some species exhibit a distinct swimming behaviour (gliding), which requires specific biomechanical attributes to generate lift and reduce drag during locomotive events. Further, a phylogenetic analysis revealed that gliding behaviour has independently evolved at least four times, which raises the question as to whether these independent lineages have also converged on a similar phenotype. Here, we test the hypothesis that gliding scallops display shell shape convergence using a combination of geometric morphometrics and phylogenetic comparative methods that evaluate patterns of multivariate trait evolution. Our findings reveal that the gliding species display less morphological disparity and significant evolutionary convergence in morphospace, relative to expectations under a neutral model of Brownian motion for evolutionary phenotypic change. Intriguingly, the phylomorphospace patterns indicate that gliding lineages follow similar evolutionary trajectories to not one, but two regions of morphological space, and subsequent analyses identified significant differences in their biomechanical parameters, suggesting that these two groups of scallops accomplish gliding in different ways. Thus, whereas there is a clear gliding morphotype that has evolved convergently across the phylogeny, functionally distinct morphological subforms are apparent, suggesting that there may be two optima for the gliding phenotype in the Pectinidae.     

Hummingbird blood traits track oxygen availability across space and time

Predictable trait variation across environments suggests shared adaptive responses via repeated genetic evolution, phenotypic plasticity or both. Matching of trait–environment associations at phylogenetic and individual scales implies consistency between these processes. Alternatively, mismatch implies that evolutionary divergence has changed the rules of trait–environment covariation. Here we tested whether species adaptation alters elevational variation in blood traits. We measured blood for 1217 Andean hummingbirds of 77 species across a 4600-m elevational gradient. Unexpectedly, elevational variation in haemoglobin concentration ([Hb]) was scale independent, suggesting that physics of gas exchange, rather than species differences, determines responses to changing oxygen pressure. However, mechanisms of [Hb] adjustment did show signals of species adaptation: Species at either low or high elevations adjusted cell size, whereas species at mid-elevations adjusted cell number. This elevational variation in red blood cell number versus size suggests that genetic adaptation to high altitude has changed how these traits respond to shifts in oxygen availability.     

Common ancestry or environmental trait filters: cross‐continental comparisons of trait–habitat relationships in tropical anuran amphibian assemblages

Aim To investigate whether trait–habitat relations in biological communities converge across three global regions. The goal is to assess the role of habitat templets in shaping trait assemblages when different assembly mechanisms are operating and to test whether trait–habitat relations reflect a common evolutionary history or environmental trait filters. Location Guiana Shield, South America; Upper Guinea Forest Block, West Africa; Borneo rain forests, Southeast Asia. Methods We compared large anuran amphibian data sets at both the regional and cross‐continental scale. We applied a combination of three‐table ordinations (RLQ) and permutation model‐based multivariate fourth‐corner statistics to test for trait–habitat relationships at both scales and used phylogenetic comparative methods to quantify phylogenetic signal in traits that enter these analyses. Results Despite the existence of significant trait–habitat links and congruent trait patterns, we did not find evidence for the existence of a universal trait–habitat relationship at the assemblage level and no clear sign for cross‐continental convergence of trait–habitat relations. Patterns rather varied between continents. Despite the fact that a number of traits were conserved across phylogenies, the phylogenetic signal varied between regions. Trait–habitat relations therefore not only reflect a common evolutionary history, but also more recently operating environmental trait filters that ultimately determine the trait composition in regional assemblages. Main conclusions Integrating trait–habitat links into analyses of biological assemblages can enhance the predictive power and general application of species assembly rules in community and macroecology, particularly when phylogenetic comparative methods are simultaneously applied. However, in order to predict trait composition based on habitat templets, trait–habitat links cannot be assumed to be universal but rather have to be individually established in different regions prior to model building. Only then can direct trait‐based approaches be useful tools for predicting fundamental community patterns.     

Comparative bioacoustics: a roadmap for quantifying and comparing animal sounds across diverse taxa

Animals produce a wide array of sounds with highly variable acoustic structures. It is possible to understand the causes and consequences of this variation across taxa with phylogenetic comparative analyses. Acoustic and evolutionary analyses are rapidly increasing in sophistication such that choosing appropriate acoustic and evolutionary approaches is increasingly difficult. However, the correct choice of analysis can have profound effects on output and evolutionary inferences. Here, we identify and address some of the challenges for this growing field by providing a roadmap for quantifying and comparing sound in a phylogenetic context for researchers with a broad range of scientific backgrounds. Sound, as a continuous, multidimensional trait can be particularly challenging to measure because it can be hard to identify variables that can be compared across taxa and it is also no small feat to process and analyse the resulting high-dimensional acoustic data using approaches that are appropriate for subsequent evolutionary analysis. Additionally, terminological inconsistencies and the role of learning in the development of acoustic traits need to be considered. Phylogenetic comparative analyses also have their own sets of caveats to consider. We provide a set of recommendations for delimiting acoustic signals into discrete, comparable acoustic units. We also present a three-stage workflow for extracting relevant acoustic data, including options for multivariate analyses and dimensionality reduction that is compatible with phylogenetic comparative analysis. We then summarize available phylogenetic comparative approaches and how they have been used in comparative bioacoustics, and address the limitations of comparative analyses with behavioural data. Lastly, we recommend how to apply these methods to acoustic data across a range of study systems. In this way, we provide an integrated framework to aid in quantitative analysis of cross-taxa variation in animal sounds for comparative phylogenetic analysis. In addition, we advocate the standardization of acoustic terminology across disciplines and taxa, adoption of automated methods for acoustic feature extraction, and establishment of strong data archival practices for acoustic recordings and data analyses. Combining such practices with our proposed workflow will greatly advance the reproducibility, biological interpretation, and longevity of comparative bioacoustic studies.     

Urbanization and its effects on personality traits: a result of microevolution or phenotypic plasticity?

Human‐altered environmental conditions affect many species at the global scale. An extreme form of anthropogenic alteration is the existence and rapid increase of urban areas. A key question, then, is how species cope with urbanization. It has been suggested that rural and urban conspecifics show differences in behaviour and personality. However, (i) a generalization of this phenomenon has never been made; and (ii) it is still unclear whether differences in personality traits between rural and urban conspecifics are the result of phenotypic plasticity or of intrinsic differences. In a literature review, we show that behavioural differences between rural and urban conspecifics are common and taxonomically widespread among animals, suggesting a significant ecological impact of urbanization on animal behaviour. In order to gain insight into the mechanisms leading to behavioural differences in urban individuals, we hand‐raised and kept European blackbirds (Turdus merula) from a rural and a nearby urban area under common‐garden conditions. Using these birds, we investigated individual variation in two behavioural responses to the presence of novel objects: approach to an object in a familiar area (here defined as neophilia), and avoidance of an object in a familiar foraging context (defined as neophobia). Neophilic and neophobic behaviours were mildly correlated and repeatable even across a time period of one year, indicating stable individual behavioural strategies. Blackbirds from the urban population were more neophobic and seasonally less neophilic than blackbirds from the nearby rural area. These intrinsic differences in personality traits are likely the result of microevolutionary changes, although we cannot fully exclude early developmental influences.     

Quantitative genetics of behavioural reaction norms: genetic correlations between personality and behavioural plasticity vary across stickleback populations

Behavioural ecologists have proposed various evolutionary mechanisms as to why different personality types coexist. Our ability to understand the evolutionary trajectories of personality traits requires insights from the quantitative genetics of behavioural reaction norms. We assayed > 1000 pedigreed stickleback for initial exploration behaviour of a novel environment, and subsequent changes in exploration over a few hours, representing their capacity to adjust their behaviour to changes in perceived novelty and risk. We found heritable variation in both the average level of exploration and behavioural plasticity, and population differences in the sign of the genetic correlation between these two reaction norm components. The phenotypic correlation was not a good indicator of the genetic correlation, implying that quantitative genetics are necessary to appropriately evaluate evolutionary hypotheses in cases such as these. Our findings therefore have important implications for future studies concerning the evolution of personality and plasticity.