Latitudinal variation of immune defense and sickness behavior in the white-crowned sparrow (Zonotrichia leucophrys) Noah T. Owen-Ashley a, * , Dennis Hasselquist b , Lars Ra ˚berg b , John C. Wingfield a,1 a Department of Biology, University of Washington, Seattle, WA 98195-1800, USA b Department of Animal Ecology, Lund University, Ecology Building, 223 62 Lund, Sweden Received 2 October 2007; received in revised form 14 December 2007; accepted 18 December 2007 Available online 5 February 2008 Abstract There is a general trend that parasitism risk declines as latitude increases. Host populations breeding at high latitudes should therefore invest less in costly immune defenses than populations breeding in temperate or tropical zones, although it is unknown if such an effect is mediated by environmental (photoperiodic) or genetic factors or both. Acquired immune function (humoral, cell-mediated) and behavioral sickness responses to lipopolysaccharide (LPS; mimics bacterial infection) were assessed in two sub- species of white-crowned sparrow (Zonotrichia leucophrys) that breed at different latitudes in western North America. Zonotrichia l. gambelii (GWCS) is a high-latitude breeder (47–68°N) while Z. l. pugetensis (PWCS) breeds at temperate latitudes (40–49°N). Cap- tive males of each subspecies were acclimated to (1) a short day (non-breeding) photoperiod (8L:16D), (2) the breeding photoperiod of PWCS (16L:8D), or (3) the breeding photoperiod of GWCS (20L:4D). Photoperiod was manipulated because shorter day lengths may enhance immune function. In support of a genetic effect, humoral responses to diphtheria–tetanus vaccination were significantly higher in PWCS compared to GWCS, regardless of photoperiod. There were no differences in cell-mediated responses to phytohem- agglutinin (PHA) between subspecies or among photoperiods. For sickness responses to LPS, a significant interaction between pho- toperiod and subspecies was found, with long day GWCS producing stronger sickness responses (losing more weight, eating less) than short day GWCS and PWCS on all day lengths. However, these effects were influenced by photoperiodic changes in body condition. In conclusion, we find evidence for genetic control of immune responses across latitude, but no support for environmen- tal (photoperiodic) regulation. Ó 2008 Elsevier Inc. All rights reserved. Keywords: Corticosterone; Cell-mediated immunity; Humoral immunity; Immune response; Latitude; Photoperiod; Sickness behavior; Testosterone; White-crowned sparrow; Zonotrichia leucophrys 1. Introduction There is a general trend for parasite and pathogen abun- dance and diversity to decrease on a global scale as geo- graphic latitude increases, and this relationship has been documented in a variety of vertebrate taxa, including fish (Rohde and Heap, 1998), birds (Grenier et al., 1975; Ben- nett et al., 1992), primates (Nunn et al., 2005) and humans (Guernier et al., 2004). Climatic and demographic factors are largely thought to regulate these gradients by limiting parasite development and transmission at higher latitudes, while creating greater infection opportunities from a more abundant and diverse pool of host species at lower lati- tudes, such as the tropics (Stromberg, 1997; Harvell et al., 2002). From a co-evolutionary standpoint, it is hypothesized that hosts should make corresponding latitu- dinal adjustments in immunological defenses, such that populations inhabiting parasite-rich environments invest 0889-1591/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.bbi.2007.12.005 * Corresponding author. Present address: Department of Wildlife Management, P.O. Box 69, North Slope Borough, Barrow, AK 99723, USA. Fax: +1 907 852 0351. E-mail address: Noah.Owen-Ashley@north-slope.org (N.T. Owen- Ashley). 1 Present address: Section of Neurobiology, Physiology, and Behavior, One Shields Avenue, University of California, Davis, CA 95616, USA. www.elsevier.com/locate/ybrbi Available online at www.sciencedirect.com Brain, Behavior, and Immunity 22 (2008) 614–625 BRAIN, BEHAVIOR, and IMMUNITY