Environmental and genetic effects shape the development of personality traits in the mangrove killifish Kryptolebias marmoratus

Consistent individual differences in behaviour are well documented, for example, individuals can be defined as consistently bold or consistently shy. To date our understanding of the mechanisms underpinning consistent individual differences in behaviour (also termed behavioural types (BTs)) remains limited. Theoretical work suggests life‐history tradeoffs drive BT variation, however, empirical support is scarce. Moreover, whilst life‐history is known to be phenotypically plastic in response to environmental conditions during ontogeny, the extent to which such plasticity drives plasticity in behavioural traits and personality remains poorly understood. Using a natural clonal vertebrate, Kryptolebias marmoratus, we control for genetic variation and investigate developmental plasticity in life‐history and three commonly studied behavioural traits (exploration, boldness, aggression) in response to three ecologically relevant environments; conspecific presence, low food and perceived risk. Simulated predation risk was the only treatment that generated repeatable behaviour i.e. personality during ontogeny. Treatments differed in their effects on mean life‐history and behavioural scores. Specifically, low food fish exhibited reduced growth rate and exploration but did not differ from control fish in their boldness or aggression scores. Conspecific presence resulted in a strong negative effect on mean aggression, boldness and exploration during ontogeny but had minimal effect on life‐history traits. Simulated predation risk resulted in increased reproductive output but had minimal effect upon average behavioural scores. Together these results suggest that life‐history plasticity/variation may be insufficient in driving variation in personality during development. Finally, using offspring derived from each rearing environment we investigate maternal effects and find strong maternal influence upon offspring size, but not behaviour. These results highlight and support the current understanding that risk perception is important in shaping personality, and that social experience during ontogeny is a major influence upon behavioural expression.     

Brain size predicts behavioural plasticity in guppies (Poecilia reticulata): An experiment

Understanding how animal personality (consistent between‐individual behavioural differences) arises has become a central topic in behavioural sciences. This endeavour is complicated by the fact that not only the mean behaviour of individuals (behavioural type) but also the strength of their reaction to environmental change (behavioural plasticity) varies consistently. Personality and cognitive abilities are linked, and we suggest that behavioural plasticity could also be explained by differences in brain size (a proxy for cognitive abilities), since accurate decisions are likely essential to make behavioural plasticity beneficial. We test this idea in guppies (Poecilia reticulata), artificially selected for large and small brain size, which show clear cognitive differences between selection lines. To test whether those lines differed in behavioural plasticity, we reared them in groups in structurally enriched environments and then placed adults individually into empty tanks, where we presented them daily with visual predator cues and monitored their behaviour for 20 days with video‐aided motion tracking. We found that individuals differed consistently in activity and risk‐taking, as well as in behavioural plasticity. In activity, only the large‐brained lines demonstrated habituation (increased activity) to the new environment, whereas in risk‐taking, we found sensitization (decreased risk‐taking) in both brain size lines. We conclude that brain size, potentially via increasing cognitive abilities, may increase behavioural plasticity, which in turn can improve habituation to novel environments. However, the effects seem to be behaviour‐specific. Our results suggest that brain size likely explains some of the variation in behavioural plasticity found at the intraspecific level.     

Plasticity of boldness in rainbow trout,Oncorhynchus mykiss: do hunger and predation influence risk-taking behaviour?

Boldness, a measure of an individual's propensity for taking risks, is an important determinant of fitness but is not necessarily a fixed trait. Dependent upon an individual's state, and given certain contexts or challenges, individuals may be able to alter their inclination to be bold or shy in response. Furthermore, the degree to which individuals can modulate their behaviour has been linked with physiological responses to stress. Here we attempted to determine whether bold and shy rainbow trout, Oncorhynchus mykiss, can exhibit behavioural plasticity in response to changes in state (nutritional availability) and context (predation threat). Individual trout were initially assessed for boldness using a standard novel object paradigm; subsequently, each day for one week fish experienced either predictable, unpredictable, or no simulated predator threat in combination with a high (2% body weight) or low (0.15%) food ration, before being reassessed for boldness. Bold trout were generally more plastic, altering levels of neophobia and activity relevant to the challenge, whereas shy trout were more fixed and remained shy. Increased predation risk generally resulted in an increase in the expression of three candidate genes linked to boldness, appetite regulation and physiological stress responses - ependymin, corticotrophin releasing factor and GABA(A) - but did not produce a significant increase in plasma cortisol. The results suggest a divergence in the ability of bold and shy trout to alter their behavioural profiles in response to internal and exogenous factors, and have important implications for our understanding of the maintenance of different behavioural phenotypes in natural populations.     

Behavioural Syndromes in Urban and Rural Populations of Song Sparrows

Animals in urban habitats are often noticeably bold in the presence of humans. Such boldness may arise due to habituation, as urban animals learn, through repeated exposure, that passing humans do not represent a threat. However, there is growing research suggesting that: (1) inherent traits, as opposed to learned behaviour, influence which species invade urban habitats, and (2) individuals exhibit individual personality traits that limit behavioural flexibility, with the possible result that not all individuals would be able to demonstrate an appropriate level of boldness in urban environments. As a result, perhaps only birds with inherently bold personalities could successfully settle in an area of high human disturbance, and further, we might also expect to see the existence of behavioural syndromes, where boldness is correlated with variation in other behavioural traits such as aggression. In this study, we examined boldness and territorial aggression in urban and rural populations of song sparrows. We found that urban birds were bolder towards humans and that urban birds also showed higher levels of territorial aggression. We also found an overall correlation between boldness and territorial aggression, suggesting that urban boldness may be part of a behavioural syndrome. However, we see no correlation between boldness and aggression in the urban population, and thus, more work is needed to determine the mechanisms accounting for high levels of boldness and aggression urban song sparrows.     

Behavioural syndrome in a solitary predator is independent of body size and growth rate

Models explaining behavioural syndromes often focus on state-dependency, linking behavioural variation to individual differences in other phenotypic features. Empirical studies are, however, rare. Here, we tested for a size and growth-dependent stable behavioural syndrome in the juvenile-stages of a solitary apex predator (pike, Esox lucius), shown as repeatable foraging behaviour across risk. Pike swimming activity, latency to prey attack, number of successful and unsuccessful prey attacks was measured during the presence/absence of visual contact with a competitor or predator. Foraging behaviour across risks was considered an appropriate indicator of boldness in this solitary predator where a trade-off between foraging behaviour and threat avoidance has been reported. Support was found for a behavioural syndrome, where the rank order differences in the foraging behaviour between individuals were maintained across time and risk situation. However, individual behaviour was independent of body size and growth in conditions of high food availability, showing no evidence to support the state-dependent personality hypothesis. The importance of a combination of spatial and temporal environmental variation for generating growth differences is highlighted.     

Individual and Sex Differences in Habituation and Neophobia in House Sparrows (Passer domesticus)

Heterogeneity in the environment favours foragers that are flexible (phenotypically plastic). However, consistent individual differences in behaviour (personality), such as in risk‐taking, might affect an individual's ability to find food, avoid predators and adjust to new conditions. It is now well known that personalities exist in many taxa, but much less is known about individual variation in plasticity. We measured the tendency to begin foraging across different levels of risk in house sparrows (Passer domesticus), using a behavioural reaction norm framework to simultaneously assess personality and plasticity. We asked whether individuals were consistently different across risk levels, and whether they differed in habituation and neophobia, both of which were treated as cases of plasticity. We found that males habituated more than females by beginning to feed sooner after repeated instances of a human disturbance in the presence of an initially unfamiliar object. Individuals of both sexes also exhibited consistent differences across trials, but did not differ in the rate of habituation beyond the difference between the sexes. When a novel object was placed in the foraging area, both sexes exhibited similar degrees of neophobia by delaying feeding. The magnitude of this change varied among birds, indicating individual differences in neophobia. Our results indicate that both personality and individual variation in plasticity exist but should be treated as independent phenomena. The presence of variation in plasticity implies that the raw material necessary for selection on neophobia exists, and that if heritable, plasticity in risk‐taking across contexts could evolve.     

Personality-dependent dispersal in the invasive mosquitofish: group composition matters

Understanding/predicting ecological invasions is an important challenge in modern ecology because of their immense economical and ecological costs. Recent studies have revealed that within-species variation in behaviour (i.e. animal personality) can shed light on the invasion process. The general hypothesis is that individuals' personality type may affect their colonization success, suggesting that some individuals might be better invaders than others. We have recently shown that, in the invasive mosquitofish (Gambusia affinis), social personality trait was an important indicator of dispersal distance, with more asocial individuals dispersing further. Here, we tested how mean personality within a population, in addition to individual personality type, affect dispersal and settlement decisions in the mosquitofish. We found that individual dispersal tendencies were influenced by the population's mean boldness and sociability score. For example, individuals from populations with more asocial individuals or with more bold individuals are more likely to disperse regardless of their own personality type. We suggest that identifying behavioural traits facilitating invasions, even at the group level, can thus have direct applications in pest management.     

Host plant effects on the behavioural phenotype of a Chrysomelid

1. The food plant quality influences feeding preferences and various life history traits of herbivorous insects. However, the effects of different host plant qualities on the behavioural phenotype have rarely been studied in behavioural ecology, especially in a pest‐crop‐framework. 2. Behavioural phenotypes of insects may not only be affected by external environmental factors, such as the host plant quality but are also shaped by internal factors, such as the sex and the age of individuals. 3. To study host plant effects on behavioural phenotypes, we reared mustard leaf beetles (Phaedon cochleariae Fabricius) either on their natural host watercress or on the crop cabbage, on which this beetle can be a pest. The behavioural phenotype was characterised twice in the adult lifetime by measuring six behavioural traits tested in distinct contexts. 4. Depending on the context, different behavioural traits were specifically affected by the host plant, the sex and/or the age. Beetles fed on cabbage became more active with age. Furthermore, the boldness tested in an unprotected environment context was influenced by the host, with beetles fed on cabbage being bolder, whereas the boldness in a hiding or predator attack context was affected by the age and/or the interaction of host plant × sex. 5. In conclusion, beetles fed on the crop cabbage develop a different behavioural phenotype compared to beetles fed on watercress. Previous results showed that beetles reared on cabbage have a higher reproductive output. Thus, beetles fed on the crop potentially express a faster pace‐of‐life.     

Individual Variation in Male Size and Behavioral Repertoire in the Sailfin Molly Poecilia latipinna

Variation among individuals in the expression of behaviors and associations of behaviors in different contexts can lead to the maintenance of behavioral polymorphisms. Individual variation in morphology is often associated with behavioral polymorphism, yet the degree to which morphology predicts behavioral phenotype is not well understood. We measured individual variation in size and behaviors in the sailfin molly, Poecilia latipinna, by comparing the behavior of individual males of different sizes across four different contexts (mating, exploratory tendency, sociability, and predator inspection). We also investigated the degree to which male size, a fixed genetic trait, influenced the expression of each behavior and associations between behaviors. We found that male mollies show strong associations between certain behaviors and only some of these are predicted by male size. For example, size has a strong influence on the courtship‐boldness axis with larger males showing higher rates of courtship displays and being bolder in predator inspection. A positive association was found between exploratory tendency, sociability, and gonopodial thrusting rates, yet the expression of these behaviors was independent of male size. Thus, sailfin mollies, like many fish species, show associations of behaviors that contribute to differences among males in personality type. The fixed genetic effect of male size at maturity influences courtship and boldness, but individual variation in exploratory tendency, sociability, and sneak copulation attempts through gonopodial thrusts is independent of male size. Such variation among males in behavioral associations within and between different contexts may slow the rate at which populations of P. latipinna can diverge in individual behaviors.     

Examining the link between personality and laterality in a feral guppy Poecilia reticulata population

This study examined whether variation in the strength and direction of lateralization in a detour task was linked with variation in three common personality measurements: boldness, activity and sociability, in a population of wild guppies Poecilia reticulata. Additionally, the aim was to determine whether any consistent correlations between these behavioural traits, known as behavioural syndromes, were present in the study population. The results revealed that all three personality traits were highly repeatable over time in both sexes. Evidence of a complex syndrome in the form of a correlation between boldness, sociability and activity was found; however, this relationship was only present in males. Males that were more active in a familiar environment emerged more quickly from shelter into a novel environment and were more social. In general, male P. reticulata were bold, active and antisocial compared to females, with these differences probably a reflection of opposing life‐history strategies. Only a weak link between the strength of cerebral lateralisation and personality was discovered and this was mediated by sex.     

Direct and indirect phenotypic effects on sociability indicate potential to evolve

The decision to leave or join a group is important as group size influences many aspects of organisms' lives and their fitness. This tendency to socialise with others, sociability, should be influenced by genes carried by focal individuals (direct genetic effects) and by genes in partner individuals (indirect genetic effects), indicating the trait's evolution could be slower or faster than expected. However, estimating these genetic parameters is difficult. Here, in a laboratory population of the cockroach Blaptica dubia, I estimate phenotypic parameters for sociability: repeatability (R) and repeatable influence (RI), that indicate whether direct and indirect genetic effects respectively are likely. I also estimate the interaction coefficient (Ψ), which quantifies how strongly a partner's trait influences the phenotype of the focal individual and is key in models for the evolution of interacting phenotypes. Focal individuals were somewhat repeatable for sociability across a 3-week period (R = 0.080), and partners also had marginally consistent effects on focal sociability (RI = 0.053). The interaction coefficient was non-zero, although in opposite sign for the sexes; males preferred to associate with larger individuals (Ψ_male = −0.129), while females preferred to associate with smaller individuals (Ψ_female = 0.071). Individual sociability was consistent between dyadic trials and in social networks of groups. These results provide phenotypic evidence that direct and indirect genetic effects have limited influence on sociability, with perhaps most evolutionary potential stemming from heritable effects of the body mass of partners. Sex-specific interaction coefficients may produce sexual conflict and the evolution of sexual dimorphism in social behaviour.     

Personality traits and behavioural profiles in the domestic canary are affected by sex and photoperiod

Personality traits and behavioural profiles are generally assumed to be stable in adulthood. Yet, it has been hypothesised that animals should cope with cyclical fluctuations by adjusting both single behaviours and suites of behaviour. Photoperiod is well known to induce hormonal and physiological changes, and these changes can in turn affect personality traits and behavioural profiles. This study is the first to explicitly investigate the influence of photoperiod on both behavioural profiles and personality traits. Six potential personality traits (within‐flock activity, ability to escape, response to threat, isolation calling, boldness and neophobia) and dominance were measured four times in 96 domestic canaries Serinus canaria (48 males and 48 females): twice during a long photoperiod (Long Days) and 6 months later twice during a short photoperiod (Short Days). Without regard to sex and photoperiod, most traits were highly repeatable, and bolder canaries were more dominant, less sensitive to an external threat and to isolation and less neophobic. In addition, the more active individuals within a flock were the more difficult to catch. Yet, both sex and photoperiod affected personality traits and behavioural profiles. Personality traits remained repeatable within each photoperiod though we observed behavioural plasticity and sex differences for response to threat, neophobia and within‐flock activity. Concerning behavioural profiles, the negative relationship between boldness and neophobia remained homogenous in both sexes during Short Days as well as during Long Days. Then, the more active individuals within a flock were the more difficult to catch in Short Days but not in Long Days. Finally, the other correlations not only varied with photoperiod but also with sex. Our study highlights the importance of photoperiod and sex in the expression of personality traits and behavioural profiles, and of the need to measure them across the whole photoperiodic cycle.     

Adaptive strategies for managing uncertainty may explain personality‐related differences in behavioural plasticity

There is growing evidence that individuals within populations show consistent differences in their behaviour across contexts (personality), and that personality is associated with the extent to which individuals adjust their behaviour as function of changing conditions (behavioural plasticity). We propose an evolutionary explanation for a link between personality and plasticity based upon how individuals manage uncertainty. Individuals can employ three categories of tactics to manage uncertainty. They can 1) gather information (sample) to reduce uncertainty, 2) show strategic (state‐dependent) preferences for options that differ in their associated variances in rewards (i.e. variance‐sensitivity), or 3) invest in insurance to mitigate the consequences of uncertainty. We explicitly outline how individual differences in the use of any of these tactics can generate personality‐related differences in behavioural plasticity. For example, sampling effort is likely to co‐vary with individual activity and exploration behaviours, while simultaneously creating population variation in reactions to changes in environmental conditions. Individual differences in the use of insurance may be associated with differences in risk‐taking behaviours, such as boldness in the face of predation, thereby influencing the degree of adaptive plasticity across individuals. Population variation in responsiveness to environmental changes may also reflect individual differences in variance‐sensitivity, because stochastic change in the environment increases variances in rewards, which may both attract and benefit variance‐prone individuals, but not variance‐averse individuals. We review the existing evidence that individual variation in strategies for managing uncertainty exist, and describe how positive‐feedbacks between sampling, variance‐sensitivity and insurance can maintain and exaggerate even small initial differences between individuals in the relative use of these tactics. Given the pervasiveness of the problem of uncertainty, alternative strategies for managing uncertainty may provide a powerful explanation for consistent differences in behaviour and behavioural plasticity for a wide range of traits.     

Variation in personality and behavioural plasticity across four populations of the great tit Parus major

1. Interest in the evolutionary origin and maintenance of individual behavioural variation and behavioural plasticity has increased in recent years. 2. Consistent individual behavioural differences imply limited behavioural plasticity, but the proximate causes and wider consequences of this potential constraint remain poorly understood. To date, few attempts have been made to explore whether individual variation in behavioural plasticity exists, either within or between populations. 3. We assayed 'exploration behaviour' among wild-caught individual great tits Parus major when exposed to a novel environment room in four populations across Europe. We quantified levels of individual variation within and between populations in average behaviour, and in behavioural plasticity with respect to (i) repeated exposure to the room (test sequence), (ii) the time of year in which the assays were conducted and (iii) the interval between successive tests, all of which indicate habituation to novelty and are therefore of functional significance. 4. Consistent individual differences ('I') in behaviour were present in all populations; repeatability (range: 0.34-0.42) did not vary between populations. Exploration behaviour was also plastic, increasing with test sequence - but less so when the interval between subsequent tests was relatively large - and time of year; populations differed in the magnitude of plasticity with respect to time of year and test interval. Finally, the between-individual variance in exploration behaviour increased significantly from first to repeat tests in all populations. Individuals with high initial scores showed greater increases in exploration score than individuals with low initial scores; individual by environment interaction ('I × E') with respect to test sequence did not vary between populations. 5. Our findings imply that individual variation in both average level of behaviour and behavioural plasticity may generally characterize wild great tit populations and may largely be shaped by mechanisms acting within populations. Experimental approaches are now needed to confirm that individual differences in behavioural plasticity (habituation) - not other hidden biological factors - caused the observed patterns of I × E. Establishing the evolutionary causes and consequences of this variation in habituation to novelty constitutes an exciting future challenge.     

Social personality trait and fitness

Several recent studies have explored various aspects of animal personality and their ecological consequences. However, the processes responsible for the maintenance of personality variability within a population are still largely unknown. We have recently demonstrated that social personality traits exist in the common lizard (Lacerta vivipara) and that the variation in sociability provides an explanation for variable dispersal responses within a given species. However, we need to know the fitness consequences of variation in sociability across environmental contexts in order to better understand the maintenance of such variation. In order to achieve this, we investigated the relationship between sociability and survival, body growth and fecundity, in one-year-old individuals in semi-natural populations with varying density. 'Asocial' and 'social' lizards displayed different fitness outcomes in populations of different densities. Asocial lizards survived better in low-density populations, while social females reproduced better. Spatiotemporal variation in environmental conditions might thus be the process underlying the maintenance of these personality traits within a population. Finally, we also discuss the position of sociability in a more general individual behavioural pattern including boldness, exploration and aggressiveness.     

Habitat quality mediates personality through differences in social context

Assessing the stability of animal personalities has become a major goal of behavioral ecologists. Most personality studies have utilized solitary individuals, but little is known on the extent that individuals retain their personality across ecologically relevant group settings. We conducted a field survey which determined that mud crabs, Panopeus herbstii, remain scattered as isolated individuals on degraded oyster reefs while high quality reefs can sustain high crab densities (>10 m^?2). We examined the impact of these differences in social context on personality by quantifying the boldness of the same individual crabs when in isolation and in natural cohorts. Crabs were also exposed to either a treatment of predator cues or a control of no cue throughout the experiment to assess the strength of this behavioral reaction norm. Crabs were significantly bolder when in groups than as solitary individuals with predator cue treatments exhibiting severally reduced crab activity levels in comparison to corresponding treatments with no predator cues. Behavioral plasticity depended on the individual and was strongest in the presence of predator cues. While bold crabs largely maintained their personality in isolation and group settings, shy crabs would become substantially bolder when among conspecifics. These results imply that the shifts in crab boldness were a response to changes in perceived predation risk, and provide a mechanism for explaining variation in behavioral plasticity. Such findings suggest that habitat degradation may produce subpopulations with different behavioral patterns because of differing social interactions between individual animals.     

Consistent behavioural traits and behavioural syndromes in pairs of the false clown anemonefish Amphiprion ocellaris

Using the social clown anemonefish Amphiprion ocellaris, whether individuals exhibited consistency in activity levels, boldness and sociability in a paired context, and whether these three behavioural traits were positively correlated within a single behavioural syndrome, was investigated. The results highlight that consistent individual differences in behaviour are expressed in a social fish and suggest that consistent behavioural traits and behavioural syndromes could influence the structure and functioning of their societies.     

Non‐consumptive effects of predation: does perceived risk strengthen the genetic integration of behaviour and morphology in stickleback?

Predators can shape genetic correlations in prey by altering prey perception of risk. We manipulated perceived risk to test whether such non‐consumptive effects tightened behavioural trait correlations in wild‐caught stickleback from high‐ compared to low‐risk environments due to genetic variation in plasticity. We expected tighter genetic correlations within perceived risk treatments than across them, and tighter genetic correlations in high‐risk than in low‐risk treatments. We identified genetic variation in plasticity, with genetic correlations between boldness, sociality, and antipredator morphology, as expected, being tighter within treatments than across them, for both of two populations. By contrast, genetic correlations did not tighten with exposure to risk. Tighter phenotypic correlations in wild stickleback may thus arise because predators induce correlational selection on environmental components of these traits, or because predators tighten residual correlations by causing environmental heterogeneity that is controlled in the laboratory. Our study places phenotypic integration firmly into an ecological context.     

Sex-Specific Aggression and Antipredator Behaviour in Young Brown Trout

Sex differences in adult behaviour are often interpreted as consequences of sexual selection and/or different reproductive roles in males and females. Sex-specific juvenile behaviour, however, has received less attention. Adult brown trout males are more aggressive than females during spawning and juvenile aggression may be genetically correlated with adult aggression in fish. We therefore tested the prediction that immature brown trout males are more aggressive and bolder than immature females. Because previous work has suggested that precocious maturation increases dominance in salmonids, we included precocious males in the study to test the prediction that early sexual maturation increase male aggression and boldness. Aggression and dominance relations were estimated in dyadic contests, whereas boldness was measured as a response to simulated predation risk using a model heron. Independent of maturity state, males initiated more than twice as many agonistic interactions as females in intersexual contests. However, males were not significantly more likely to win these contests than females. The response to a first predator attack did not differ between sex categories, but males reacted less to a second predator attack than females. Sexual maturity did not affect the antipredator response in males. Since there is no evidence from field studies that stream-living immature male and female salmonids differ in growth rate, it appears unlikely that the sex differences demonstrated are behavioural consequences of sex-specific investment in growth. It seems more likely that sex-specific behaviour arises as a correlated response to sexually selected gene actions promoting differential behaviour in adult males and females during reproduction. Alternatively, sex differences may develop gradually during juvenile life, because a gradual developmental program should be less costly than a sudden behavioural change at the onset of sexual maturity.     

Shaped by the past,acting in the present: transgenerational plasticity of anti‐predatory traits

Phenotypic expression can be altered by direct perception of environmental cues (within‐generation phenotypic plasticity) and by the environmental cues experienced by previous generations (transgenerational plasticity). Few studies, however, have investigated how the characteristics of phenotypic traits affect their propensity to exhibit plasticity within and across generations. We tested whether plasticity differed within and across generations between morphological and behavioral anti‐predator traits of Physa acuta, a freshwater snail. We reared 18 maternal lineages of P. acuta snails over two generations using a full factorial design of exposure to predator or control cues and quantified adult F₂ shell size, shape, crush resistance, and anti‐predator behavior – all traits which potentially affect their ability to avoid or survive predation attempts. We found that most morphological traits exhibited transgenerational plasticity, with parental exposure to predator cues resulting in larger and more crush‐resistant offspring, but shell shape demonstrated within‐generation plasticity. In contrast, we found that anti‐predator behavior expressed only within‐generation plasticity such that offspring reared in predator cues responded less to the threat of predation than control offspring. We discuss the consequences of this variation in plasticity for trait evolution and ecological dynamics. Overall, our study suggests that further empirical and theoretical investigation is needed in what types of traits are more likely to be affected by within‐generational and transgenerational plasticity.