Sexual selection and animal personality

Consistent individual behavioural tendencies, termed “personalities”, have been identified in a wide range of animals. Functional explanations for personality have been proposed, but as yet, very little consideration has been given to a possible role for sexual selection in maintaining differences in personality and its stability within individuals. We provide an overview of the available literature on the role of personality traits in intrasexual competition and mate choice in both human and non‐human animals and integrate this into a framework for considering how sexual selection can generate and maintain personality. For this, we consider the evolution and maintenance of both main aspects of animal personality: inter‐individual variation and intra‐individual consistency.     

Evolutionary genomics of animal personality

Research on animal personality can be approached from both a phenotypic and a genetic perspective. While using a phenotypic approach one can measure present selection on personality traits and their combinations. However, this approach cannot reconstruct the historical trajectory that was taken by evolution. Therefore, it is essential for our understanding of the causes and consequences of personality diversity to link phenotypic variation in personality traits with polymorphisms in genomic regions that code for this trait variation. Identifying genes or genome regions that underlie personality traits will open exciting possibilities to study natural selection at the molecular level, gene-gene and gene-environment interactions, pleiotropic effects and how gene expression shapes personality phenotypes. In this paper, we will discuss how genome information revealed by already established approaches and some more recent techniques such as high-throughput sequencing of genomic regions in a large number of individuals can be used to infer micro-evolutionary processes, historical selection and finally the maintenance of personality trait variation. We will do this by reviewing recent advances in molecular genetics of animal personality, but will also use advanced human personality studies as case studies of how molecular information may be used in animal personality research in the near future.     

Energy metabolism and animal personality

In this paper we show how animal personality could explain some of the large inter-individual variation in resting metabolic rate (MR) and explore methodological and functional linkages between personality and energetics. Personality will introduce variability in resting MR measures because individuals consistently differ in their stress response, exploration or activity levels, all of which influence MR measurements made with respirometry and the doubly-labelled water technique. Physiologists try to exclude these behavioural influences from resting MR measurements, but animal personality research indicates that these attempts are unlikely to be successful. For example, because reactive animals "freeze" when submitted to a stress, their MR could be classified as "resting" because of immobility when in fact they are highly stressed with an elevated MR. More importantly, recent research demonstrating that behavioural responses to novel and highly artificial stimuli are correlated with both behaviour and fitness under more natural circumstances calls into question the wisdom of excluding these behavioural influences on MR measurements. The reason that intra-specific variation in resting MR are so weakly correlated with daily energy expenditure (DEE) and fitness, may be that the latter two measures fully incorporate personality while the former partially excludes its influence. Because activity, exploration, boldness and aggressiveness are energetically costly, personality and metabolism should be correlated and physiological constraints may underlie behavioural syndromes. We show how physiological ecologists can better examine behavioural linkages between personality and metabolism, as required to better understand the physiological correlates of personality and the evolutionary consequences of metabolic variability.     

动物个性研究进展

"个性"是指不同时空条件下动物种群个体间行为的稳定差异。大量的理论和实验性研究表明,个性差异在动物界普遍存在,其是种群多度和分布、物种共存及群落构建的重要驱动因子。介绍了动物个性的概念、分类及衡量指标,将前人测量个性类型的方法加以总结;随后介绍了动物个性的生态学意义,尤其是个性对动物生活史策略、种群分布与多度、群落结构和动态、生态系统功能和过程以及疾病与信息传播等的影响。在此基础上,进一步分析了在人类活动增加等全球变化背景下,动物个性如何调控动物个体行为、种群和群落动态对这些环境变化的响应。阐述了动物个性的形成与维持机制,并对未来的研究方向进行了展望。     

Parasitism and the evolutionary ecology of animal personality

The ecological factors responsible for the evolution of individual differences in animal personality (consistent individual differences in the same behaviour across time and contexts) are currently the subject of intense debate. A limited number of ecological factors have been investigated to date, with most attention focusing on the roles of resource competition and predation. We suggest here that parasitism may play a potentially important, but largely overlooked, role in the evolution of animal personalities. We identify two major routes by which parasites might influence the evolution of animal personality. First, because the risk of acquiring parasites can be influenced by an individual's behavioural type, local parasite regimes may impose selection on personality traits and behavioural syndromes (correlations between personality traits). Second, because parasite infections have consequences for aspects of host 'state', parasites might induce the evolution of individual differences in certain types of host behaviour in populations with endemic infections. Also, because infection often leads to specific changes in axes of personality, parasite infections have the potential to decouple behavioural syndromes. Host-parasite systems therefore provide researchers with valuable tools to study personality variation and behavioural syndromes from a proximate and ultimate perspective.     

Rating vs. coding in animal personality research

Animal personality research has become increasingly popular over the past few decades. The two main methods used to examine individual differences in animals are rating and coding. The rating method involves human scoring of an animal's behavioral tendencies along various behavioral dimensions, such ratings are typically based on the human rater's experience with the animal. The coding method also requires humans to score an animal's behavior, but differs in that the scoring is based on the animal's immediate behavior in a specific context. This brief report describes the use of both the rating and coding methods to examine personality within a group of 10 Garnett's bushbabies (Otolemur garnettii). The results indicated that individual personalities do exist in bushbabies, but also suggested that the rating method is heavily influenced by the rater's experience with an animal. Consequently, it is important that the nature of the rater's interactions with the target animals be considered when using the rating method to assess animal personality. Zoo Biol 29:509–516, 2010. © 2009 Wiley‐Liss, Inc.     

The development of animal personality: relevance,concepts and perspectives

Recent studies of animal personality have focused on its proximate causation and its ecological and evolutionary significance, but have mostly ignored questions about its development, although an understanding of the latter is highly relevant to these other questions. One possible reason for this neglect is confusion about many of the concepts and terms that are necessary to study the development of animal personality. Here, we provide a framework for studying personality development that focuses on the properties of animal personality, and considers how and why these properties may change over time. We specifically focus on three dimensions of personality: (1) contextual generality at a given age or time, (2) temporal consistency in behavioural traits and in relationships between traits, and (3) the effects of genes and experience on the development of personality at a given age or life stage. We advocate using a new approach, contextual reaction norms, to study the contextual generality of personality traits at the level of groups, individuals and genotypes, show how concepts and terms borrowed from the literature on personality development in humans can be used to study temporal changes in personality at the level of groups and individuals, and demonstrate how classical developmental reaction norms can provide insights into the ways that genes and experiential factors interact across ontogeny to affect the expression of personality traits. In addition, we discuss how correlations between the effects of genes and experience on personality development can arise as a function of individuals' control over their own environment, via niche‐picking or niche‐construction. Using this framework, we discuss several widely held assumptions about animal personality development that still await validation, identify neglected methodological issues, and describe a number of promising new avenues for future research.     

Metamorphosis and animal personality: a neglected opportunity

Developmental perspectives represent an underutilized area of animal personality research, in spite of their obvious importance in biology. Animals that undergo metamorphosis are particularly neglected and represent a unique in situ experimental opportunity to study how personality differences are associated with physiological, morphological, or ecological traits over development.     

Personality,empathy and attitudes to animal welfare

Abstract

A total of 833 students completed a four-part questionnaire which measured demographic factors (sex, education, vegetarianism, religiousness), attitudes to animal experimentation, personality (Big Five) and empathy. Attitudes to animal experimentation factored into five interpretable factors, and multiple regression analyses were used to examine the extent to which demographic factors, personality and empathy predicted these. Sex, vegetarianism, Agreeableness, Openness, Extraversion and empathy were significant predictors of all these factors. Results showed an interpretable set of correlates that were similar to previous studies in the area. As with previous research findings, the measures used predicted only a small amount of variance with respect to attitudes to animals.     

Parasitism, predation and the evolution of animal personalities

Trade-offs between behavioural traits promoting high life-history productivity and mortality may fuel the evolution of animal personalities. We propose that parasites, including pathogens, impose fitness costs comparable to those from predators, and influence the adaptiveness of personality traits associated with productivity (PAPs). Whether personality traits are adaptive or not may also depend on individual immunological capacity. We illustrate this using a conceptual example in which the optimal level of PAPs depends on predation, parasitism and host compensation (resistance and tolerance) of parasitism's negative effects. We assert that inherent differences in host immune function can produce positive feedback loops between resource intake and compensation of parasitism's costs, thereby providing variation underlying the evolution of stable personalities. Our approach acknowledges the condition dependence of immune function and co-evolutionary dynamics between hosts and parasites.     

Novel environmental enrichment may provide a tool for rapid assessment of animal personality: a case study with giant pandas (Ailuropoda melanoleuca)

Historically, the assessment of nonhuman animal personality has included a variety of methods--from direct behavioral observations in a variety of test situations to assessments provided by animal caretakers or trainers. Careful observation of how animals in zoos interact with novel enrichment may provide reliable insight into their personality. This study sought to describe a process for evaluating whether different methods of assessing personality result in similar conclusions. The study exposed 4 giant pandas at the Smithsonian National Zoological Park and Zoo Atlanta to 10 novel enrichment items and recorded their behavior. Keepers also rated each panda on 23 behavioral characteristics on a survey. The study obtained individual behavior profiles for each panda. Significant differences across individuals in both the novel enrichment trials and keeper surveys formed the basis for the profiles. These methods also provided some insight into differences between the sexes that--based on the natural history of giant pandas--are qualitatively similar to what would be expected. The study found some consistency between assessment methods. However, there is a need for further study to validate these measures in a larger sample of giant pandas.     

Luigi Galvani's path to animal electricity

In spite of the historical importance of the research that, in the second half of the 18th century, led Luigi Galvani (1737-1798) to lay down the foundation of modern electrophysiology, his scientific personality is largely misrepresented in science history and in popular imagery. He is still considered as a pioneer that by chance incurred some surprising experimental observations and was incapable of pursuing his research in a coherent way. In contrast with these views, Galvani was a high-standard scientist who succeeded, with the strength of experimental science, in demonstrating, in animals, electricity in a condition of disequilibrium between the interior and the exterior of excitable fibres. This electricity, called 'animal electricity', was deemed responsible for nerve conduction. By studying the scientific endeavours of Galvani, through his published and unpublished material, and by situating them in the historical context of the physiology of the Enlightenment, this paper attempts to trace the elusive and complex path that led Galvani to his extraordinary discovery.     

Companion animal adoption study

To better understand the outcomes of companion animal adoptions, Bardsley & Neidhart Inc. conducted a series of 3 surveys over a 1-year period with dog and cat owners who had adopted their pet through either a (a) Luv-A-Pet location, (b) Adopt-a-thon, or (c) traditional shelter. This article suggests opportunities to improve owners' perceptions of their pets and the adoption process through (a) providing more information before adoption about pet health and behaviors, (b) providing counseling to potential adopters to place pets appropriately, and (c) educating adopters to promote companion animal health and retention. Results demonstrate that the pet's relationship to the family unit, such as where the pet sleeps and how much time is spent with the pet, is related to the amount of veterinary care the companion animal receives, and to long-term retention. Satisfaction and retention are attributed to the pet's personality, compatibility, and behavior, rather than demographic differences among adopters or between adoption settings. The age of the companion animal at adoption, the intended recipient, and presence of children in the home also play a role. Health problems were an issue initially for half of all adopted pets, but most were resolved within 12 months. Roughly one fourth of adopters who no longer have their companion animal said their pet died. Characteristics of pets that died support the contention that spaying and neutering profoundly affects a companion animal's life span. Although retention is similar for dogs and cats, mortality is higher among cats in the first year after adoption.     

Exploring the connection between emergent animal personality and fitness using a novel individual-based model and decision tree approach

The connection between reproductive fitness and animal personality is not fully understood. Using computer simulations and machine learning, we found high accuracy rules that predict which personalities are associated with fitness for two correlated measures of components of fitness applied a posteriori for classificatory purposes: fitness component (1) in terms of survival and short-term reproductive success, and fitness component (2) in terms of long term reproductive success which is indirectly related to survival of the parents. Animals are represented in the abstract as individuals with a genome that through time develops into certain characteristic behaviors and personalities. To the best of our knowledge, this is the first simulation study of its kind that extracts rules to investigate the link between personality and fitness. Clearly separated behaviors between fit and non-fit individuals emerged through the evolution of the population over time without top-down processing. Moreover, we did not employ a pre-defined fitness function, in order to minimize any possible biases toward a specific type of behavior. With respect to fitness component (1), we found that individuals with one of two extreme values of a personality trait (either bold or fearful) tend to be most fit, which agrees with empirical studies. With respect to fitness component (2), we found that when resources are low, fit individuals search for food whereas if food is abundant, they focus on reproduction, thereby suggesting the context dependence of fitness related behaviors. Once again, these results agree with empirical studies.     

Effect of diet on the structure of animal personality

There is increasing interest in the proximate factors that underpin individual variation in suites of correlated behaviours. In this paper, we propose that dietary macronutrient composition, an underexplored environmental factor, might play a key role. Variation in macronutrient composition can lead to among-individual differentiation in single behaviours (‘personality’ ) as well as among-individual covariation between behaviours (‘behavioural syndromes’ ). Here, we argue that the nutritional balance during any life stage might affect the development of syndrome structure and the expression of genes with pleiotropic effects that influence development of multiple behaviours, hence genetic syndrome structure. We further suggest that males and females should typically differ in diet-dependent genetic syndrome structure despite a shared genetic basis. We detail how such diet-dependent multivariate gene-environment interactions can have major repercussions for the evolution of behavioural syndromes.     

The etiology of personality function: the University of British Columbia Twin Project.

The UBC Twin Project is an on-going study of personality and personality disorder that has collected personality data on approximately 1000 adult volunteer twin pairs. The primary purpose of the study is to develop and validate measures of the major forms of personality disorder as a quantitative alternative to the classificatory system first proposed by the DSM-III using the standard methods of personality and behavioural genetics research. To date, the study has explored the univariate and multivariate relationships between the major personality and personality disorder inventories, and their relationships to other psychopathologies including the mood and anxiety disorders and key psychological variables, such as cognitive ability, attachment and attitudes. The results have several implications for personality and personality disorders, most notably a rationalized diagnostic/nosological system to enhanced measurement instruments that index and reflect the influence of specific genetic and environmental influences.     

Rapid divergence of animal personality and syndrome structure across an arid-aquatic habitat matrix

Intraspecific trait variation, including animal personalities and behavioural syndromes, affects how individual animals and populations interact with their environment. Within-species behavioural variation is widespread across animal taxa, which has substantial and unexplored implications for the ecological and evolutionary processes of animals. Accordingly, we sought to investigate individual behavioural characteristics in several populations of a desert-dwelling fish, the Australian desert goby (Chlamydogobius eremius). We reared first generation offspring in a common garden to compare non-ontogenic divergence in behavioural phenotypes between genetically interconnected populations from contrasting habitats (isolated groundwater springs versus hydrologically variable river waterholes). Despite the genetic connectedness of populations, fish had divergent bold-exploratory traits associated with their source habitat. This demonstrates divergence in risk-taking traits as a rapid phenotypic response to ecological pressures in arid aquatic habitats: neophilia may be suppressed by increased predation pressure and elevated by high intraspecific competition. Correlations between personality traits also differed between spring and river fish. River populations showed correlations between dispersal and novel environment behaviours, revealing an adaptive behavioural syndrome (related to dispersal and exploration) that was not found in spring populations. This illustrates the adaptive significance of heritable behavioural variation within and between populations, and their importance to animals persisting across contrasting habitats.     

Personality: bridging the literatures from human psychology and behavioural ecology

The concept of personality has recently begun to attract a great deal of interest in behavioural ecology. However, there is also a large and mature literature on personality within human psychology. These two bodies of work have developed independently and at present make rather little reference to one another. The current paper has two main objectives. First, we seek to acquaint behavioural ecologists with the principal ideas and issues found in the human personality psychology literature. Second, we explore how ideas from the behavioural ecology literature might help advance research in human personality psychology. We suggest strong potential for convergence between the two literatures in the near future. Common themes of this future unified science of personality include the conception of personality traits as reaction norms, a commitment to the importance of direct measurement of behaviour, investigation of both proximate and ultimate explanations for personality variation, and a concern with the impact of personality variation on survival and reproductive success.     

High in situ repeatability of behaviour indicates animal personality in the beadlet anemone Actinia equina (Cnidaria)

'Animal personality' means that individuals differ from one another in either single behaviours or suites of related behaviours in a way that is consistent over time. It is usually assumed that such consistent individual differences in behaviour are driven by variation in how individuals respond to information about their environment, rather than by differences in external factors such as variation in microhabitat. Since behavioural variation is ubiquitous in nature we might expect 'animal personality' to be present in diverse taxa, including animals with relatively simple nervous systems. We investigated in situ startle responses in a sea anemone, Actinia equina, to determine whether personalities might be present in this example of an animal with a simple nervous system. We found very high levels of repeatability among individuals that were re-identified in the same locations over a three week sampling period. In a subset of the data, where we used tide-pool temperature measurements to control for a key element of variation in microhabitat, these high levels of repeatability remained. Although a range of other consistent differences in micro-habitat features could have contributed to consistent differences between the behaviour of individuals, these data suggest the presence of animal personality in A. equina. Rather than being restricted to certain groups, personality may be a general feature of animals and may be particularly pronounced in species with simple nervous systems.