Research paper Behavioral phenotype relates to physiological differences in immunological and stress responsiveness in reactive and proactive birds Elizabeth A. Pusch, Kristen J. Navara ⇑ Department of Poultry Science, The University of Georgia, Athens, GA 30602, USA article info Article history: Received 20 October 2017 Revised 25 January 2018 Accepted 26 January 2018 Available online xxxx Keywords: Chicken Immunity LPS Personality PHA abstract It has now been demonstrated in many species that individuals display substantial variation in coping styles, generally separating into two major behavioral phenotypes that appear to be linked to the degree of physiological stress responsiveness. Laying hens are perfect examples of these dichotomous pheno- types; white laying hens are reactive, flighty, and exhibit large hormonal and behavioral responses to both acute and chronic stress, while brown laying hens are proactive, exploratory, and exhibit low hor- monal and behavioral responses to stress. Given the linkages between stress physiology and many other body systems, we hypothesized that behavioral phenotype would correspond to additional physiological responses beyond the stress response, in this case, immunological responses. Because corticosterone is widely known to be immunosuppressive, we predicted that the reactive white hens would show more dampened immune responses than the proactive brown hens due to their exposure to higher levels of corticosterone throughout life. To assess immune function in white and brown hens, we compared febrile responses, corticosterone elevations, feed consumption, and egg production that occurred in response an injection of lipopolysaccharide (LPS) or saline, inflammatory responses to phytohemagglutinin (PHA) injection in the toe web, innate phagocytic activity in whole blood, and antibody responses to an injection of Sheep Red Blood Cells (SRBCs). Contrary to our predictions, white hens had significantly greater swel- ling of the toe web in response to PHA and showed a greater inhibition of feeding and reproductive out- put in response to LPS. These results indicated that reactive individuals are more reactive in both stress and immunological responsiveness. Ó 2018 Elsevier Inc. All rights reserved. 1. Introduction Animals of the same species can often be divided into behav- ioral phenotypes that appear to suit them for life in different envi- ronments. These distinct phenotypes are characterized by consistent variation in aggressive, fear, and exploratory behaviors, and also by differences in physiological responses to stress (Baugh et al., 2013, 2012; Carere et al., 2003, 2010; Cockrem, 2012; Fraisse and Cockrem, 2006; Groothuis and Carere, 2005). Scientists now define these behavioral phenotypes using the terms ‘‘reactive” and ‘‘proactive” (Koolhaas et al., 1999; Groothuis and Carere, 2005). Proactive animals tend to have a bold and fast response to novel environments or stimuli (i.e., they are quick explorers, less fearful, and more aggressive) and produce smaller physiological responses (e.g. corticosterone elevations) to acute (Carere et al., 2010; Cockrem, 2007) and chronic stressors (Pusch et al., 2017). Reactive animals tend to have a slow and shy response (i.e., they are cautious explorers, more fearful, and more passive) and pro- duce stronger physiological responses to acute (Carere et al., 2010; Fraisse and Cockrem, 2006) and chronic stressors (Pusch et al., 2017). While studies characterizing behavioral phenotypes have focused on the responses of animals to stressful stimuli, the differ- ences in the activity of the hypothalamic-pituitary-adrenal axis between these behavioral groups may impact many downstream physiological and behavioral processes including foraging, metabo- lism, and immunity (Baugh et al., 2012; Carere et al., 2010, 2003; Cockrem, 2007; Groothuis and Carere, 2005, Koolhaas, 2008; Koolhas et al., 2010). These reactions are integral to an organism’s ability to respond to a stressor, and to return to, and maintain, homeostasis. Indeed, other physiological responses have been shown to co-vary with behavioral phenotype (Huff et al., 2013; Koolhaas, 2008; Koolhaas et al., 1999; Korte et al., 1996; van Oers et al., 2011). For example, mice with short attack latencies (SAL) had low plasma corticosterone levels and greater levels of serotonin receptor mRNA and serotonin receptor binding sites in https://doi.org/10.1016/j.ygcen.2018.01.027 0016-6480/Ó 2018 Elsevier Inc. All rights reserved. ⇑ Corresponding author at: 110 Cedar Street, Poultry Science Building, Athens, GA 30602, USA. E-mail address: knavara@uga.edu (K.J. Navara). General and Comparative Endocrinology xxx (2018) xxx–xxx Contents lists available at ScienceDirect General and Comparative Endocrinology journal homepage: www.elsevier.com/locate/ygcen Please cite this article in press as: Pusch, E.A., Navara, K.J. Behavioral phenotype relates to physiological differences in immunological and stress respon- siveness in reactive and proactive birds. Gen. Comp. Endocrinol. (2018), https://doi.org/10.1016/j.ygcen.2018.01.027