Immunocompetence of breeding females is sensitive to cortisol levels but not to communal rearing in the degu (Octodon degus) Luis A. Ebensperger a, ⁎, Cecilia León a , Juan Ramírez-Estrada a , Sebastian Abades a,f , Loren D. Hayes b , Esteban Nova c , Fabián Salazar c , Joydeep Bhattacharjee d , María Inés Becker c,e a Departamento de Ecología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Casilla 114-D, Santiago, Chile b Department of Biological and Environmental Sciences, University of Tennessee at Chattanooga, Chattanooga, TN 37403, USA c Fundación Ciencia y Tecnología para el Desarrollo (FUCITED), Santiago, Chile d Department of Biology, University of Louisiana, Monroe, LA 71209, USA e Biosonda Corporation, Santiago, Chile f Instituto de Ecología y Biodiversidad (IEB), Las Palmeras 3425, Ñuñoa, Santiago, Chile HIGHLIGHTS • No evidence that communal rearing enhances female reproductive success and survival • No evidence that communal rearing enhances offspring immunocompetence or survival • Females with high fecal glucocorticoids (FGC) increased lymphocytes and monocytes • Females with low FGC experienced increases in N:L ratios, neutrophils, and total IgG • Immunocompetence of females is sensitive to FGC but not to communal rearing abstract article info Article history: Received 13 August 2014 Received in revised form 10 December 2014 Accepted 11 December 2014 Available online 12 December 2014 Keywords: Immunocompetence Octodon degus Concholepas hemocyanin Direct fitness Cortisol Sociality Social immunity Communal rearing One hypothesis largely examined in social insects is that cooperation in the context of breeding benefits individ- uals through decreasing the burden of immunocompetence and provide passive immunity through social con- tact. Similarly, communal rearing in social mammals may benefit adult female members of social groups by reducing the cost of immunocompetence, and through the transfer of immunological compounds during allonursing. Yet, these benefits may come at a cost to breeders in terms of a need to increase investment in indi- vidual immunocompetence. We examined how these potential immunocompetence costs and benefits relate to reproductive success and survival in a natural population of the communally rearing rodent, Octodon degus. We related immunocompetence (based on ratios of white blood cell counts, total and specific immunoglobulins of G isotype titers) and fecal glucocorticoid metabolite (FGC) levels of adults immunized with hemocyanin from the mollusk Concholepas concholepas to measures of sociality (group size) and communal rearing (number of breed- ing females). Offspring immunocompetence was quantified based on circulating levels of the same immune pa- rameters. Neither female nor offspring immunocompetence was influenced by communal rearing or sociality. These findings did not support that communal rearing and sociality enhance the ability of females to respond to immunological challenges during lactation, or contribute to enhance offspring condition (based on immuno- competence) or early survival (i.e., to 3 months of age). Instead, levels of humoral and cellular components of im- munocompetence were associated with variation in glucorcorticoid levels of females. We hypothesize that this covariation is driven by physiological (life-history) adjustments needed to sustain breeding. © 2014 Elsevier Inc. All rights reserved. 1. Introduction Group-living or sociality involves spatial and temporal proximity among individuals that results from the mutual attraction rather than from attraction to the same resource or physical condition [55,72]. Relevant attributes of sociality include group size, group stability, and the extent to which group members display cooperative or competitive interactions [16,72,100]. Thus, sociality is thought to increase with group size, but also with the extent to which group members cooperate to attain food, avoid predators, or rear their offspring, among other as- pects [27]. Functionally, sociality is thought to evolve when fitness ben- efits, namely decreased predation risk, enhanced access to resources, or decreased thermoregulatory costs [19,28,55], outweigh inherent costs Physiology & Behavior 140 (2015) 61–70 ⁎ Corresponding author. E-mail address: lebensperger@bio.puc.cl (L.A. Ebensperger). http://dx.doi.org/10.1016/j.physbeh.2014.12.028 0031-9384/© 2014 Elsevier Inc. All rights reserved. Contents lists available at ScienceDirect Physiology & Behavior journal homepage: www.elsevier.com/locate/phb