Individual Differences In Plasticity Research Articles

Bolder together: conformity drives behavioral plasticity in eastern gartersnakes

Personality traits drive individual differences in behaviour that are consistent across time and context. Personality limits behavioural plasticity, which could lead to maladaptive choices if animals cannot adapt their behavior to changing conditions. Here, we assessed consistency and flexibility in one personality trait, boldness, across non-social and social contexts in eastern gartersnakes (Thamnophis sirtalis sirtalis). Snakes explored a novel open arena either alone or in a pair. Pairs were assigned based on the data from the solo trials, such that each snake was paired once with a bolder and once with a less bold partner. We predicted that snakes would conform when in a social context, displaying plasticity in their personality, and causing boldness scores to converge. We found that snakes were consistent within contexts (solo or paired), but changed their behavior across contexts (from solo to paired). Plasticity in boldness resulted from an interaction between conformity and repeatable individual differences in plasticity. In line with some data on other species, snakes conformed more when they were the less bold partner. Personality reflects a consistent bias in decision-making, but our results highlight that the cognitive processes that drive the expression of personality traits in behavior are flexible and sensitive to social context. We show that both consistency and plasticity combine to shape snake social behavior in ways that are responsive to competition. This pattern of behavior may be particularly beneficial for species in which group-living is seasonal.

Personality differences between sexes are present in a peaceful lizard, but not in an aggressive one: a chemical communication trial in two Liolaemus species

Animal personality can be defined as behavioral individual consistency across contexts and time, and sociability may facilitate it. Boldness and exploration can be considered as social conflictive behaviors and in lizards, social scent can either diminish or promote social conflicts. We studied boldness and exploration in Liolaemus albiceps Lobo and Laurent, 1995 and Liolaemus coeruleus Cei and Ortiz, 1983, and tested whether Liolaemus albiceps, a lesser aggressive species, presents higher individual consistency in a socially nonconflictive behavior, such as escape (boldness). We also expect Liolaemus coeruleus, a more aggressive species, to present higher individual consistency in exploration, which is socially more conflictive behavior. We exposed lizards to their own conspecifics and control scent treatments. We calculated the repeatability for boldness and exploration, analyzed their correlation, and tested for behavioral plasticity. Boldness and exploration were repeatable in Liolaemus albiceps at species level, with females showing highly repeatable boldness, and males, highly repeatable exploration. Liolaemus coeruleus exhibited no significant repeatability for either behavior. There was no correlation between these two behaviors, and both species showed plasticity. Liolaemus albiceps individuals were bolder and explored less under conspecific scents. Liolaemus coeruleus individuals explored less in presence of their own scents than novelty scents, and presented interindividual variation in plasticity. A peaceful lifestyle may favor behavioral consistency within individuals, whereas a more aggressive lifestyle may constrain within and among individual consistency in a chemical communication context. However, individual differences in plasticity could counterbalance this constraint.

Individual differences in song plasticity in response to social stimuli and singing position.

Individual animals can react to the changes in their environment by exhibiting behaviors in an individual‐specific way leading to individual differences in phenotypic plasticity. However, the effect of multiple environmental factors on multiple traits is rarely tested. Such a complex approach is necessary to assess the generality of plasticity and to understand how among‐individual differences in the ability to adapt to changing environments evolve. This study examined whether individuals adjust different song traits to varying environmental conditions in the collared flycatcher (Ficedula albicollis), a passerine with complex song. We also aimed to reveal among‐individual differences in behavioral responses by testing whether individual differences in plasticity were repeatable. The presence of general plasticity across traits and/or contexts was also tested. To assess plasticity, we documented (1) short‐scale temporal changes in song traits in different social contexts (after exposition to male stimulus, female stimulus or without stimuli), and (2) changes concerning the height from where the bird sang (singing position), used as a proxy of predation risk and acoustic transmission conditions. We found population‐level relationships between singing position and both song length (SL) and complexity, as well as social context‐dependent temporal changes in SL and maximum frequency (MF). We found among‐individual differences in plasticity of SL and MF along both the temporal and positional gradients. These among‐individual differences in plasticity were repeatable. Some of the plastic responses correlated across different song traits and environmental gradients. Overall, our results show that the plasticity of bird song (1) depends on the social context, (2) exists along different environmental gradients, and (3) there is evidence for trade‐offs between the responses of different traits to different environmental variables. Our results highlight the need to consider individual differences and to investigate multiple traits along multiple environmental axes when studying behavioral plasticity.

Nest defence behavioural reaction norms: testing life-history and parental investment theory predictions.

Predation is the primary source of reproductive failure in many avian taxa and nest defence behaviour against predators is hence an important aspect of parental investment. Nest defence is a complex trait that might consistently differ among individuals (personality), while simultaneously vary within individuals (plasticity) according to the reproductive value of the offspring. Both complementary aspects of individual variation can influence fitness, but the causality of links with reproductive success remains poorly understood. We repeatedly tested free-living female great tits (Parus major) for nest defence (hissing) behaviour across the nesting cycle, by presenting them with a model predator. Hissing behaviour was highly repeatable but, despite population-level plasticity, we found no support for individual differences in plasticity. Path analysis revealed that repeatable differences in hissing behaviour had no direct effect on nest success or fledgling number. However, our best supported path-model showed that more fiercely hissing females laid smaller clutches, with clutch size in turn positively influencing fledgling number, suggesting that females are most likely facing a trade-off between investment in nest defence and reproduction. Strong stabilizing selection for optimal plasticity, in combination with life-history trade-offs, might explain the high repeatability of nest defence and its link with reproductive success.

Personalities influence spatial responses to environmental fluctuations in wild fish.

Although growing evidence supports the idea that animal personality can explain plasticity in response to changes in the social environment, it remains to be tested whether it can explain spatial responses of individuals in the face of natural environmental fluctuations. This is a major challenge in ecology and evolution as spatial dynamics link individual‐ and population‐level processes.In this study, we investigated the potential of individual personalities to predict differences in fish behaviour in the wild. Specifically, our goal was to answer if individual differences in plasticity of space use to sea surface temperature could be explained by differences in personality along the reactive–proactive axis.To address this question, we first conducted repeated standard laboratory assays (i.e., open‐field test, novel object test and mirror stimulation test) to assess the personality type of 76 wild‐caught Atlantic cod (Gadus morhua). Next, we released the fish back into the sea and monitored their spatial behaviour over large temporal (16 months) and spatial (a whole fjord) scales, using high‐resolution acoustic tracking.We demonstrate that (a) cod personality traits are structured into a proactive–reactive syndrome (proactive fish being more bold, exploratory and aggressive), (b) mean depth use of individuals is mainly driven by sea temperature and (c) personality is a significant predictor of home range changes in the wild, where reactive, but not proactive, individuals reduced their home range as sea temperature increased.These findings expand our understanding of the ecological consequences of animal personality and the mechanisms shaping spatial dynamics of animals in nature.

Why do protective factors protect? An evolutionary developmental perspective

Abstract A growing body of research has identified a list of protective factors that decrease the likelihood of an individual engaging in criminal and antisocial behaviour. However, despite substantial empirical advances in our understanding of the factors that protect against offending, relatively little theoretical work has been directed at explaining why these factors serve a protective function and the notion of protective factors, like risk factors, is conceptually problematic. In this article I argue that we can advance our understanding of what protective factors are and why they serve a protective function by taking an evolutionary developmental perspective. More specifically, an evolutionary informed framework is provided that outlines two broad models for understanding individual differences in antisocial and prosocial behaviour. First, I suggest that individual differences in antisocial (and prosocial behaviour) are linked to the development of alternative life history strategies in response to different environmental contexts. More specifically, I argue that ‘protective’ factors can often be conceptualised in terms of features of the environment and/or feature of individuals that promote and/or reflect the development of slow life history strategies. Second, drawing from recent research on individual differences in plasticity I highlight how our conceptualisation of protective (and, indeed, risk) factors is contingent on the interaction between individual susceptibility to environmental influence and relevant environmental contexts. In other words, often what counts as a ‘protective’ factor depends on individual differences in plasticity. Inevitably, as our understanding of why protective factors protect improves, there will be advances in the nature and scope of our interventions to improve prosocial outcomes and prevention efforts will be enhanced.

Surprising flexibility in parental care revealed by experimental changes in offspring demand

Parental behaviour often exhibits plasticity to factors expected to affect the benefits or costs of care. For example, parent songbirds typically increase their provisioning behaviour as nestlings mature. Several mechanisms exist that could allow parents to track nestling age and provide appropriate care. We performed a short-term experiment on house sparrows, Passer domesticus, in which offspring of different ages were exchanged to assess the level of flexibility parents exhibit and the likely cues they use. We found that a pair's rate of food delivery, an individual parent's visit rate to the nest, the duration of a foraging trip, and both the time a parent was in the nest and how long they perched near the nest after emerging from feeding nestlings changed according to the age of the offspring at the time. This shift in parenting was evident by the second visit after the swap. The amount of food brought per trip did not change with either natural or manipulated age. While females spent more time in the nest than males, there were no sex differences in the responses to the experiment. Food delivery rate increased nestling mass gain during each phase of the experiment, suggesting that parental plasticity in delivery was beneficial to offspring. However, there was an additional effect of the experiment on nestling weight gain, suggesting possible effects of food type brought during each phase of the experiment. Parent sparrows appear to use cues of offspring age over a time span that differs greatly from the natural time course of changes in nestling demand. This extension of plasticity into unnatural conditions has implications for understanding individual differences in plasticity and how at least some organisms might adjust to rapid and unusual environmental change.

Highly variable, unpredictable activity patterns in invasive, but not native amphipod species

Behavioral differences between native and introduced species may contribute to the invasiveness of certain species. This includes differences at the species level, consistent variation among individuals (“personality”) and within-individual variation (e.g., behavioral plasticity). Here, we investigated swimming activity of individuals from four different amphipod species occurring in the river Rhine system, three of which were native or naturalized (>100 years present) while one is a recent invader (Dikerogammarus villosus, <25 years present). At the species level, D. villosus did not show higher average swimming activity than the three non-invasive species. However, the non-invasive species, on average, changed their behavior predictably over the course of the experiment (“average behavioral plasticity”), while D. villosus did not exhibit any consistent change in activity. At the individual level, D. villosus exhibited greater among- and within-individual variation in activity levels than all non-invasive species. The non-invasive species further showed significant individual differences in plasticity, that is, individuals of these species differed consistently in how they changed their activity over time. The high within-individual variation in D. villosus translated into a lack of consistent individual differences in plasticity in this species. We hypothesize that the highly variable and unpredictable patterns of individual activity variation in D. villosus might help this successful invader to cope with new environmental conditions encountered in the river Rhine system.

Differential susceptibility to the environment: Are developmental models compatible with the evidence from twin studies?

According to models of differential susceptibility, the same neurobiological and temperamental traits that determine increased sensitivity to stress and adversity also confer enhanced responsivity to the positive aspects of the environment. Differential susceptibility models have expanded to include complex developmental processes in which genetic variation interacts with exposure to early environmental factors, such as prenatal stress hormones and family conflict. In this study I employed a simulation approach to explore whether, and under what conditions, developmental models of differential susceptibility are compatible with the cumulative findings from twin studies of personality and behavior, which consistently show sizable effects of genetic and nonshared environmental factors and small to negligible effects of the shared environment. Simulation results showed that, to a first approximation, current alternative models of differential susceptibility are all equally compatible with the evidence from twin research; that sizable interaction effects involving individual differences in plasticity are plausible, but only if direct environmental effects are correspondingly weak; and that a major role of shared environmental factors is plausible in early development (consistent with the developmental mechanisms postulated in the differential susceptibility literature) but not in later development. These results support the general plausibility of differential susceptibility models and suggest some realistic constraints on their assumptions. (PsycINFO Database Record

Plasticity as a developing trait: exploring the implications.

Individual differences in plasticity have been classically framed as genotype-by-environment interactions, with different genotypes showing different reaction norms in response to environmental conditions. However, research has shown that early experience can be a critical factor in shaping an individual's plasticity to later environmental factors. In other words, plasticity itself can be investigated as a developing trait that reflects the combined action of an individual's genes and previous interactions with the environment. In this paper I explore some implications of the idea that the early environment modulates long-term plasticity, with an emphasis on plasticity in behavioral traits. I begin by focusing on the mechanisms that mediate plasticity at the proximate level, and discussing the possibility that some traits may work as generalized mediators of plasticity by affecting the sensitivity of multiple phenol types across developmental contexts. I then tackle the complex problem of the evolution of reaction norms for plasticity. Next, I consider a number of potential implications for research on parental effects and phenotypic matching, and conclude by discussing how plasticity may become a target of evolutionary conflict between parents and offspring. In total, I aim to show how the idea of plasticity as a developing trait offers a rich source of questions and insights that may inform future research in this area.

Experimental food restriction reveals individual differences in corticosterone reaction norms with no oxidative costs.

Highly plastic endocrine traits are thought to play a central role in allowing organisms to respond rapidly to environmental change. Yet, not all individuals display the same degree of plasticity in these traits, and the costs of this individual variation in plasticity are unknown. We studied individual differences in corticosterone levels under varying conditions to test whether there are consistent individual differences in (1) baseline corticosterone levels; (2) plasticity in the hormonal response to an ecologically relevant stressor (food restriction); and (3) whether individual differences in plasticity are related to fitness costs, as estimated by oxidative stress levels. We took 25 wild-caught house sparrows into captivity and assigned them to repeated food restricted and control treatments (60% and 110% of their daily food intake), such that each individual experienced both food restricted and control diets twice. We found significant individual variation in baseline corticosterone levels and stress responsiveness, even after controlling for changes in body mass. However, these individual differences in hormonal responsiveness were not related to measures of oxidative stress. These results have implications for how corticosterone levels may evolve in natural populations and raise questions about what we can conclude from phenotypic correlations between hormone levels and fitness measures.

Reproductive allocation between the sexes, across natural and novel habitats, and its impact on genetic diversity

Allocation to reproductive mode (sexual and asexual) can vary depending on environmental conditions but is often examined at the population level, whereas selection acts upon the individual. We examined individual variation in reproductive mode to identify how the interaction of sex and the environment affect population genetic diversity. Using the plant Marchantia inflexa, we tested whether reproductive allocation pattern varies consistently between males and females and among plants collected from different environments, and determined if morphological responses were the result of individual plasticity or genetic differences. We then quantified genetic variability between the different environments and between the sexes. Male and female plants were collected from two strikingly different habitats within the same region: along natural sites (rivers) and along novel human-modified sites (roadsides). Using a common garden approach, we found a strong sex by habitat interaction: male and female responses differed significantly by their source habitat. For females, relative to river-collected, road-collected plants had higher growth and asexual reproduction, while the pattern was reversed, although not significant, for males. Genetic differentiation was significant between the two habitats with no evidence of individual differences in plasticity for growth, but there was a genotype effect for asexual propagule production. Males and females did not differ genetically; but river-collected plants with lower sexual potential were more diverse than roadside-collected plants, possibly the result of founder events. These results show that individual variation in reproduction is controlled by the interaction of both the environment and genetics. Due to different selection pressures between natural and novel habitats, there are observable differences in life history traits with an associated evolutionary response to the novel habitat.

Between-individual differences in behavioural plasticity within populations: causes and consequences

Behavioural traits are characterized by their labile expression: behavioural responses can, in principle, be up- and down-regulated in response to moment-to-moment changes in environmental conditions. Evidence is accumulating that individuals from the same population differ in the degree and extent of this form of phenotypic plasticity. We here discuss how such between-individual differences in behavioural plasticity can result from additive and interactive effects of genetic make-up and past environmental conditions, and under which conditions natural selection might favour this form of between-individual variation. We highlight how spatial or temporal variation in the environment, in combination with competition among individuals, can promote adaptive individual differences in plasticity; and we detail how differences in plasticity can emerge as a result of selection pressures induced by social interactions or as a response to between-individual differences in state. We further discuss both ecological and evolutionary consequences of individual differences in plasticity. We outline, for example, how individual differences in plasticity can have knock-on effects on the rate of evolution; and how such differences can enhance the stability and persistence of populations.

Personality and plasticity: consistent responses within-, but not across-temperature situations in crabs

Recent research suggests that repeated assays of behaviour, conducted both within and across situations, could reveal important insights into two traditionally distinct areas of study: animal personality and individual differences in behavioural plasticity. However, at present relatively few studies present such data, and few consider how changing abiotic conditions affect behavioural plasticity. Individual differences in metabolic rate have been suggested as a proximate mechanism promoting personality, leading one to speculate that individual differences in metabolic sensitivity to temperature may affect behavioural responses in ectotherms. At present, only one study (out of two) has tested for and shown individual differences in behavioural responses to temperature. Here, we repeatedly assayed the behaviour of a marine crab across a narrow range of temperatures to test for individual differences in responses to temperature. We observed large inter-individual differences in behaviour that were consistent over time at a given temperature (evidence for personality), and individual differences in responses to temperature (evidence for plasticity). This study adds to the very scant literature on ectotherm behavioural sensitivity to temperature, and suggests the phenomenon might be widespread. We speculate about the role of metabolism as a proximate mechanism that might explain these individual differences in plasticity and make suggestions for future research to test this hypothesis.

Balancing sampling and specialization: an adaptationist model of incremental development

Development is typically a constructive process, in which phenotypes incrementally adapt to local ecologies. Here, we present a novel model in which natural selection shapes developmental systems based on the evolutionary ecology, and these systems adaptively guide phenotypic development. We assume that phenotypic construction is incremental and trades off with sampling cues to the environmental state. We computed the optimal developmental programmes across a range of evolutionary ecological conditions. Using these programmes, we simulated distributions of mature phenotypes. Our results show that organisms sample the environment most extensively when cues are moderately, not highly, informative. When the developmental programme relies heavily on sampling, individuals transition from sampling to specialization at different times in ontogeny, depending on the consistency of their sampled cue set; this finding suggests that stochastic sampling may result in individual differences in plasticity itself. In addition, we find that different selection pressures may favour similar developmental mechanisms, and that organisms may incorrectly calibrate development despite stable ontogenetic environments. We hope our model will stimulate adaptationist research on the constructive processes guiding development.

Individual differences in plasticity and sampling when playing behavioural games

When engaged in behavioural games, animals can adjust their use of alternative tactics until groups reach stable equilibria. Recent theory on behavioural plasticity in games predicts that individuals should differ in their plasticity or responsiveness and hence in their degree of behavioural adjustment. Moreover, individuals are predicted to be consistent in their plasticity within and across biological contexts. These predictions have yet to be tested empirically and so we examine the behavioural adjustment of individual nutmeg mannikins (Lonchura punctulata), gregarious ground-feeding passerines, when playing two different social foraging games: producer-scrounger (PS) and patch-choice (PC) games. We found: (i) significant individual differences in plasticity and sampling behaviour in each of the two games, (ii) individual differences in sampling behaviour were consistent over different test conditions within a game (PC) and over a six month period (PS), (iii) but neither individual plasticity nor sampling behaviour was correlated from one social foraging game to another. The rate at which birds sampled alternative tactics was positively associated with seed intake in PS trials but negatively associated in PC trials. These results suggest that games with frequency dependence of pay-offs can maintain differences in behavioural plasticity but that an important component of this plasticity is group- and/or context-specific.

The Nature (and Nurture?) of Plasticity in Early Human Development.

The effect of early experience is a long-standing concern in developmental psychology. Gaining further insight into the nature of human plasticity is central to efforts to prevent problems in development from arising and promote positive functioning. Evolutionary reasoning suggests that children should vary in their susceptibility to environmental influences, including parenting. Evidence indicates that rather than some children, such as those with negatively emotional temperaments or certain genotypes, being simply more vulnerable to the adverse effects of negative experiences, as commonly assumed, they may actually be more susceptible to both positive and negative experiences. In addition to raising questions about the nature of plasticity in human development, this article highlights unknowns regarding the role of nature and nurture in shaping individual differences in plasticity, including whether recent research linking maternal stress during pregnancy with child behavior problems illuminates a process whereby fetal programming shapes the child's susceptibility to postnatal environmental influences. Throughout this article, we raise concern about the potentially distorting influence that psychology's disproportionate focus on the adverse effect of negative experiences on developmental problems has on our understanding of human plasticity, and we propose that researchers should pay more attention to the positive side of the plasticity equation.

Plasticity of memory for new learning in very old age: A story of major loss?

Longitudinal survivors of the Berlin Aging Study (N = 96, mean age = 84 years, range 75-101 years) were instructed and trained in a mnemonic skill to examine plasticity of episodic memory performance in very old age. Performance gains after mnemonic instruction were modest, and most individuals were unable to further enhance their performance during 4 sessions of mnemonic practice. Whereas the proportion of variance explained by measures from the broad fluid-ability domain (e.g., perceptual speed) increased with training, the proportion of variance explained by crystallized-ability domain (e.g., word knowledge) and sociobiographical variables decreased. Furthermore, prior 6-year longitudinal changes (loss) in perceptual speed predicted individual differences in plasticity. Results suggest that aging-induced biological factors are a prominent source of individual differences in cognitive plasticity in very old age.

The senses and intelligence of the Chinese dancing mouse

For a few days during the first month of post-natal life the dancing mice which I have studied respond definitely to sounds, but neither direct nor indirect methods of testing auditory sensitiveness furnish any evidence of it in the adult. Brightness vision is fairly acute; color vision is poorly developed. I have some evidence of the discrimination of red and blue, and of red and green, but no evidence that blue and green can be distinguished. In visual discrimination the mice apparently depend upon brightness differences. The behavior of the dancing mouse is readily modifiable. Choice, by exclusion, of one of two objects which differ in brightness, with electrical stimulation in the case of a wrong choice, indicates that from 40 to 100 repetitions of an experience is necessary for the formation of a perfect habit. Such a modification of behavior lasts for from two to five weeks. Modifications of behavior occur more rapidly in the male than in the female. Individual differences in plasticity and in the permanency of modification are marked.