Dominance status predicts response to nonsocial forced movement stress in the green anole lizard (Anolis carolinensis) Jessica Plavicki 1 , Eun-Jin Yang 2 , Walter Wilczynski * Department of Psychology and Institute for Neuroscience, University of Texas, 1 University Station A8000, Austin, TX 78712-0187, USA Received 15 April 2003; received in revised form 29 September 2003; accepted 15 October 2003 Abstract We used changes in body color and eyespot formation, two somatic indices of stress controlled mainly by catecholamine activity, to compare the reactions of dominant and subordinate male green anole lizards (Anolis carolinensis) to a nonsocial stressor, forced movement. Individual males were pretested by subjecting them to 10 min of forced movement induced by chasing them around their home cage with a slender wooden stick. Stress responses were assayed via changes in body color (progressive darkening from green to brown indicating increasing stress) and expression of a black postorbital eyespot (which appears with increasing catecholaminergic stress responses). Lizards were paired and allowed to form stable dominant/subordinate relationships for 2 weeks. After that period of stable social status, dominants and subordinates were separated and subjected to the same forced-movement stress. There was no difference between experimental groups in the pretest. After assuming positions in the dominance hierarchy, however, dominant males showed reduced somatic indicators of stress and were quicker to recover from the stress. The data suggest that animals that assumed the dominant position decreased their stress response relative to the pretest, while animals that assumed the subordinate position increased their stress response relative to the pretest. The results indicate that dominant social status may have advantages beyond the realm of social interactions by enhancing an individual’s ability to tolerate other, nonsocial stressful events. D 2003 Elsevier Inc. All rights reserved. Keywords: Forced movement; Dominant; Subordinate; Anolis carolinensis; Stress 1. Introduction In many social and territorial species, aggressive social interactions lead to the establishment of social hierarchies in which some animals obtain dominant, and some subordi- nate, roles. Dominant animals are identified as such by their ability to win fights, hold desirable territories or gain access to females. In natural social assemblies, dominant status often means greater access to females and hence a greater opportunity to mate, and greater access to other resources such as food. Dominant and subordinate social status may coincide with differences in endocrinological state, although the pattern of tonic levels seems to differ greatly by species and context, including the stability of the relationship. Dominant males are often marked by higher testosterone levels compared to subordinate conspecifics, and, converse- ly, in many species subordinates have higher levels of adrenal stress hormones, specifically corticosterone [1–5]. This pattern is, however, often not observed, as there are several studies that failed to find differences in one or both of these hormones with social status, or even a reverse of this pattern (reviewed in Refs. [3,6,7]; see also Refs. [8– 10]). Much more consistently observed are differences in acute hormonal and physiological stress responses induced by social aggressive interactions coinciding with different social status (reviewed in Refs. [3,6,11]; see also Refs. [12 – 14]). During aggressive encounters in olive baboons, for example, dominant males show a rapid increase in gluco- corticoid and testosterone concentrations, which then quick- ly return to baseline following the social encounter. In contrast, subordinate males show more gradual, sustained increases in glucocorticoid concentrations but quick and 0031-9384/$ – see front matter D 2003 Elsevier Inc. All rights reserved. doi:10.1016/j.physbeh.2003.10.009 * Corresponding author. Tel.: +1-512-475-8499; fax: +1-512-471- 5935. E-mail address: wilczynski@psy.utexas.edu (W. Wilczynski). 1 Current address: Neuroscience Training Program, 1300 University Ave., University of Wisconsin, Madison, WI 53703, USA. 2 Current address: Department of Biological Sciences, 903 Fairchild MC 2430, Columbia University, New York, NY 10027, USA. Physiology & Behavior 80 (2004) 547 – 555