Coping styles in animals: current status in behavior and stress-physiology J.M. Koolhaas a, * , S.M. Korte b , S.F. De Boer a , B.J. Van Der Vegt a , C.G. Van Reenen b , H. Hopster b , I.C. De Jong a,b , M.A.W. Ruis b , H.J. Blokhuis b a Department of Animal Physiology, University of Groningen, P.O. Box 14, 9750 AA Haren, The Netherlands b DLO-Institute for Animal Science and Health (ID-DLO), Department of Behavior, Stress Physiology and Management, P.O. Box 65, 8200 AB Lelystad, The Netherlands Received 1 May 1999 Abstract This paper summarizes the current views on coping styles as a useful concept in understanding individual adaptive capacity and vulnerability to stress-related disease. Studies in feral populations indicate the existence of a proactive and a reactive coping style. These coping styles seem to play a role in the population ecology of the species. Despite domestication, genetic selection and inbreeding, the same coping styles can, to some extent, also be observed in laboratory and farm animals. Coping styles are characterized by consistent behavioral and neuroendocrine characteristics, some of which seem to be causally linked to each other. Evidence is accumulating that the two coping styles might explain a differential vulnerability to stress mediated disease due to the differential adaptive value of the two coping styles and the accompanying neuroendocrine differentiation.  1999 Elsevier Science Ltd. All rights reserved. Keywords: Coping; Aggression; Stress; Disease; Corticosterone 1. Introduction Psychosocial factors have long been recognized as impor- tant in health and disease both in man and in animals. It is not the physical characteristics of a certain aversive stimu- lus but rather the cognitive appraisal of that stimulus, which determines its aversive character and whether a state commonly described as stress is induced. The impact of aversive stimuli or stressors is determined by the ability of the organism to cope with the situation [1,2]. Several defini- tions of coping can be given [3]. In the present paper, we prefer to use the term coping as the behavioral and physio- logical efforts to master the situation [3,4]. Successful coping depends highly on the controllability and predict- ability of the stressor [5,6]. A consistent finding across species is that whenever environmental stressors are too demanding and the individual cannot cope, its health is in danger. For this reason, it is important to understand the mechanisms and factors underlying the individual’s capa- city to cope with environmental challenges. A wide variety of medical, psychological and animal studies demonstrate that individuals may differ in their coping capacities. Factors that have been shown to affect the individual’s coping capacity include genotype, development, early experience, social support, etc. Since many studies in humans indicate that coping mechanisms are important in health and disease [7], researchers have tried for a long time to determine the individual vulnerability to stress-related diseases using estimates of the individual coping capacity. One approach concerns attempts to classify coping responses into distinct coping styles. A coping style can be defined as a coherent set of behavioral and physiological stress responses which is consistent over time and which is characteristic to a certain group of individuals. It seems that coping styles have been shaped by evolution and form general adaptive response patterns in reaction to everyday challenges in the natural habitat. The concept of coping styles has been used in a wide variety of animal species (see Table 1). Despite the widespread use of the concept, it is not without debate [8]. This is due to several flaws in the studies using the concept. First, not all studies fulfill the criterion of coping style as a coherent set of behavioral and physiological characteristics because only one para- meter has been studied. Second, the extent to which clearly distinct coping styles can be distinguished has been ques- tioned [8,9]. Special attention will be given here to the frequency distribution of coping styles in a population, the consistency over time and the one-dimensional character of the concept of coping styles. Finally, one may wonder to Neuroscience and Biobehavioral Reviews 23 (1999) 925–935 PERGAMON NEUROSCIENCE AND BIOBEHAVIORAL REVIEWS NBR 376 0149-7634/99/$ - see front matter  1999 Elsevier Science Ltd. All rights reserved. PII: S0149-7634(99)00026-3 www.elsevier.com/locate/neubiorev * Corresponding author. Tel.: +31-50-3632338; fax: +31-50-3632331. E-mail address: koolhaas@biol.rug.nl (J.M. Koolhaas)