Brain Behav Evol 2007;70:215–217 DOI: 10.1159/000105484
Published online: September 18, 2007
Preface: Plasticity and Diversity in Behavior and Brain Function – Important Raw Material for Natural Selection? Øyvind Øverli Department of Animal and Aquacultural Sciences, Norwegian University of Life Sciences, Ås, Norway
The concept that humans show consistent individual differences in personality is familiar to us all, and most people would agree with the definition suggested by Pervin and John [1997], who stated that personality is: ‘Those characteristics of individuals that describe and account for consistent patterns of feeling, thinking, and behaving’. In other words: If what a man does in a certain situation predicts his behavior the next time he is in a similar situation, or even his behavior in other contexts, he has a personality. Behavioral correlation across situations, i.e. the analogue of personality, have recently been documented by ethologists and behavioral ecologists in a broad range of species, including several mammals, birds, lizards, amphibians, fish, mollusks, and arthropods [see e.g. Gosling, 2001; Bell and Stamps, 2004; Sinn and Moltschaniwskyj, 2005]. Referring to the fact that suites of correlated traits are often described as syndromes, Sih et al. [2004] coined the term behavioral syndromes, and pointed out that this phenomenon can have important ecological and evolutionary implications. For instance, the notion of behavioral syndromes implies limited behavioral plasticity. Limited plasticity, in turn, may pose problem in rapidly changing environments, such as humandisturbed habitats [Sol and Lefebvre, 2000; Sol et al., 2002]. Another question is how variation is maintained in a population. In other words, why does a population not simply drift towards a homogeneous group of the most successful phenotypes? © 2007 S. Karger AG, Basel 0006–8977/07/0704–0215$23.50/0 Fax +41 61 306 12 34 E-Mail
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There is no doubt that interest in both ultimate and proximate causes of individual variation is increasing. In a recent paper, Wolf et al. [2007] demonstrate how lifehistory theory can be used to explain the continued presence of divergent phenotypes, or personalities. Regarding the question of limited plasticity, an impetus of the 2006 Karger Workshop was to point out that behavioral states have physiological correlates, and physiology may control behavior as much as behavior controls physiology. In some cases, neurobiological mechanisms that cause variation in behavior are quite plastic and modified by experience, in other cases certain traits appear to be life-long characteristics. This symposium’s keynote lecturer, Jaap Koolhaas, and co-authors [Koolhaas et al., 1999] were among the first to point out how genetic and epigenetic factors combine to generate a relatively stable trait characteristic that confers differential adaptation to environmental conditions such as population density, social stability and food availability. The aim of the symposium was to synthesize current knowledge of proximate and ultimate mechanisms involved in maintaining individual variation in behavior, focusing on the relationship between brain structural plasticity, cognitive processes, and behavioral outcome in comparative and mammalian models. During the symposium, we were shown several examples of both heritable and apparently consistent trait associations [e.g. Veenema and Neumann, 2007; Schjolden and Winberg, 2007], and rapidly modifiable responses [Burmeister, Øyvind Øverli Department of Animal and Aquacultural Sciences Norwegian University of Life Sciences PO Box, NO–1432 Ås (Norway) Tel. +47 4150 6222, Fax +47 6496 5101, E-Mail
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2007]. Social interaction is one of the most well studied factors that can modify both behavior and physiology, and several contributors focused on the effects of social interaction. The complexity of this topic was well illustrated in the symposium: Sensitivity to social challenge varies during an animal’s life-history [Wommack and Delville, 2007]; and events early in hierarchy formation may be as, or more, important for neurobiological impact as what happens during daily social interaction [Sørensen et al., 2007]. Furthermore, pre-existing differences in physiology may determine social rank [Korzan and Summers, 2007], hence it is not necessarily straightforward to disentangle causes and consequences of particular events in an animal’s life. In a recent review Øverli et al. [2007] argued that behavioral syndromes observed in behavioral ecology [Sih et al., 2004], stress coping style [Koolhaas et al., 1999], and psychological and behavioral components of personality [Gosling, 2001] may all be reflections of the same phenomenon: individuality in the stress response. I would like to repeat this argument here: Stress has acute and long lasting effects on the neuroendocrine signaling systems controlling physiological, emotional, and behavioral responses. Taking into account that behaviors can not be performed or emotions experienced without simultaneous physiological activation, one must conclude that individual variation in stress coping ability is probably central in shaping most or all aspects of both animal and human personality. In any case, understanding individual differences in stress coping ability has become a paramount task in bio-
logical psychiatry and stress research [Susman et al., 1999; Cavigelli and McClintock, 2003; Bartolomucci et al., 2005; Korte et al., 2005; Koolhaas et al., 2007], and it has become obvious that both genetic and environmental factors [e.g. social interactions and previous exposure to stress] contribute to extensive inter-individual variation in how stressful experience affects behavior and physiology. I feel that Cliff Summers summed the field up in a very precise and elegant manner when, at the end of our plenum discussion in Atlanta, he stated: ‘This is obviously a multi-layered chicken-and-egg question, and can someone explain how it all hangs together?’ With that, we ended the session, and with that I end my introduction. Professor Summers’ question is hereby passed on to the symposium contributors, the audience, and the rest of the scientific community.
Acknowledgements I would like to use this opportunity to thank the J.B. Johnston Club Program committee who organized the meeting program, and took on all the numerous practical tasks during the meeting: Cathy McCormick, Ed Rosa-Molinar, and Cliff Summers. Blinda McClelland, as always, was central in the actual workshop organizing as well as the final editing of the papers. Karger Publishers represented by Dr. Thomas Karger is heartfully thanked for the support, without which this workshop would simply not have come about. Finally I would like to thank Brain Behavior and Evolution’s editor-in-chief, Walter Wilczynski, and Matthew Grober for their advice both concerning the actual symposium and the production of this journal issue.
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Korzan WJ, Summers CH (2007) Behavioral diversity and neurochemical plasticity: Selection of stress coping strategies that define social status. Brain Behav Evol 70:257–266. Øverli Ø, Sørensen C, Pulman KGT, Pottinger TG, Korzan W, Summers CH, Nilsson G (2007) Evolutionary background for stresscoping styles: Relationships between physiological, behavioral, and cognitive traits in non-mammalian vertebrates. Neurosci Biobehav Rev 31:396–412. Pervin LA, John, OP (1997) Personality: Theory and Research. New York, Wiley. Sih A, Bell A, Johnson JC (2004) Behavioral syndromes: an ecological and evolutionary overview. Trends Ecol Evol 19: 372–378.
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