Journal of Thermal Biology 93 (2020) 102706 Available online 26 August 2020 0306-4565/© 2020 Elsevier Ltd. All rights reserved. Decrease in preferred temperature in response to an immune challenge in lizards from cold environments in Patagonia, Argentina Fernando Duran * , Jorgelina M. Boretto, Nora R. Ibargüengoytía Laboratorio de Eco-fsiología e Historia de Vida de Reptiles, INIBIOMA, CONICET-Universidad Nacional del Comahue, Quintral 1250, 8400, Bariloche, Argentina A R T I C L E INFO Keywords: Liolaemus sarmientoi Lipopolysaccharide Thermoregulation Body condition Infection Hypothermia ABSTRACT In ectotherms, the likelihood of surviving an infection is determined by the effciency of thermoregulation, the availability of a variety of thermal microenvironments, the individual’s health status, and the virulence of the infective agent. Physiological and behavioral demands related to an effcient immune response entail a series of costs that compete with other vital activities, specifcally energy storage, growth, reproduction, and maintenance functions. Here, we characterize the thermal biology and health status by the presence of injuries, ectoparasites, body condition, and individual immune response capacity (using phytohemagglutinin in a skin-swelling assay) of the southernmost lizards of the world, Liolaemus sarmientoi, endemic to a sub-optimal, cold environment in Patagonia, Argentina. In particular, we study the effect of a bacterial endotoxin (lipopolysaccharide; LPS- treatment) on thermoregulation. We found that the feld-active body temperature (T b ) was much lower than the preferred body temperature (T p ) obtained in the laboratory. All the individuals were in good body condition at the beginning of the experiments. The phytohemagglutinin test caused detectable thickening in sole-pads at 2 h and 24 h post-assay in males and non-pregnant females, indicating a signifcant innate immune response. In the experimental immune challenge, the individuals tended to prefer a low body temperature after LPS-treatment (2 h post-injection) and developed hypothermia, while the control individuals injected with phosphate buffered saline (PBS), maintained their body temperature throughout the trial. In both the LPS-treatment and PBS-control individuals, BC declined during the experiment. Hypothermia may allow this southernmost species to optimize the use of their energetic resources and reduce the costs of thermoregulation in a cold-temperate environment where they rarely attain the mean T p (35.16 ◦ C) obtained in laboratory. 1. Introduction In ectotherms, selection of microhabitats to attain optimal body temperatures for physiological demands is relevant since it directly in- fuences growth (Angilletta et al., 2004), reproduction (Fern´ andez et al., 2015, 2017), digestion (Plasman et al., 2019) and the effective activa- tion of the immune system (Kluger, 1986; Evans et al., 2015; Duran et al., 2019), among other functions. Ectothermic vertebrates regulate body temperature primarily by behavioral thermoregulation when exposed to spatial and temporal variation in ambient heat sources (Belliure and Carrascal, 1998). In particular, reptiles tend to keep their body temperature in a range close to their thermal preference (T p ) assumed to represent the body temperature that optimizes physiological performance of many enzymatic reactions (Sinervo, 1990; Hertz, 1993; Seebacher and Franklin, 2005). Nevertheless, the attainment of T p de- pends mainly on the availability of a range of thermal microenvironments for thermoregulation that narrows at higher lati- tudes and altitudes (Graae et al., 2012; Zamora-Camacho et al., 2015). Maintaining body temperature to optimize physiological functions can be energetically costly (Bennett and Ruben, 1979; Alford and Lut- terschmidt, 2012; Brewster et al., 2013) and partially dependent on body condition (Deen and Hutchison, 2001). In particular, the produc- tion of fever by behavioral thermoregulation in response to an infectious pathogen, functioning to minimize the impact of the infection (reviewed in Rakus et al., 2017), sometimes may be detrimental to the individual due to the high energetic requirements that it entails (Romanovsky and Szekely, 1998; Deen and Hutchison, 2001). Indeed, thermoregulation can be modelled as pathogens exerting selection pressures on their hosts (Graham et al., 2011; Zamora-Camacho et al., 2015). The attainment of high body temperatures (T b ) entails greater time spent basking in detriment to other social functions such as territorial defense or courtship (Vicenzi et al., 2019) and results in higher energy * Corresponding author. E-mail address: fernandoduran@comahue-conicet.gob.ar (F. Duran). Contents lists available at ScienceDirect Journal of Thermal Biology journal homepage: http://www.elsevier.com/locate/jtherbio https://doi.org/10.1016/j.jtherbio.2020.102706 Received 11 May 2020; Received in revised form 20 August 2020; Accepted 21 August 2020