1 3 J Comp Physiol B DOI 10.1007/s00360-014-0835-y ORIGINAL PAPER Thermoregulatory plasticity in free-ranging vervet monkeys, Chlorocebus pygerythrus Alwyn Lubbe · Robyn S. Hetem · Richard McFarland · Louise Barrett · Peter S. Henzi · Duncan Mitchell · Leith C. R. Meyer · Shane K. Maloney · Andrea Fuller Received: 26 February 2014 / Revised: 12 May 2014 / Accepted: 28 May 2014 © Springer-Verlag Berlin Heidelberg 2014 inactive. These low minimum body temperatures were associated with low black globe temperature (GLMM, β = 0.046, P < 0.001), short photoperiod (β = 0.010, P < 0.001) and low rainfall over the previous 2 months, which we used as a proxy for food availability (β = 0.001, P < 0.001). Despite the lower average winter minimum body temperatures, there was no change in the lower modal body temperature between winter and summer. Therefore, unlike the regulated physiological adjustments proposed for torpor or hibernation, these minimum winter body tem- peratures did not appear to reflect a regulated reduction in body temperature. The thermoregulatory plasticity never- theless may have fitness benefits for vervet monkeys. Keywords Bio-logging · Climate change · Heterothermy · Primate · Body temperature Introduction In seasonally-variable habitats, mammals are faced with the challenge of maintaining body temperature while being exposed to dynamic thermal environments and contend- ing with fluctuations in food and water availability. At low environmental temperatures, typically in conjunction with food scarcity, some mammals—termed heterotherms— employ physiological mechanisms such as torpor or hiber- nation (i.e., prolonged torpor) that result in a decrease in energy expenditure (Geiser 2004). Torpor is defined as a state of inactivity and reduced responsiveness (IUPS Thermal Commission 2001), typically associated with a temporary, but substantial, reduction in body temperature below body temperature thresholds of about 35 °C (Willis 2007) to 30 °C (Barclay et al. 2001). However, recent stud- ies have revealed significant seasonal and daily variation Abstract We used implanted miniature data loggers to obtain the first measurements of body temperature from a free-ranging anthropoid primate. Vervet monkeys (Chlo- rocebus pygerythrus) living in a highly seasonal, semi- arid environment maintained a lower mean 24-h body temperature in winter (34.6 ± 0.5 °C) than in summer (36.2 ± 0.1 °C), and demonstrated increased heterothermy (as indexed by the 24-h amplitude of their body tempera- ture rhythm) in response to proximal environmental stress- ors. The mean 24-h amplitude of the body temperature rhythm in summer (2.5 ± 0.1 °C) was lower than that in winter (3.2 ± 0.4 °C), with the highest amplitude for an individual monkey (5.6 °C) recorded in winter. The higher amplitude of the body temperature rhythm in winter was a consequence primarily of lower 24-h minimum body tem- peratures during the nocturnal phase, when monkeys were Communicated by I. D. Hume. A. Lubbe (*) · R. S. Hetem · R. McFarland · L. Barrett · D. Mitchell · L. C. R. Meyer · S. K. Maloney · A. Fuller Brain Function Research Group, Faculty of Health Sciences, School of Physiology, University of the Witwatersrand, 7 York Road, Medical School, Parktown, Johannesburg 2193, South Africa e-mail: alwynlubbe@gmail.com L. Barrett · P. S. Henzi Department of Psychology, University of Lethbridge, Lethbridge, Canada P. S. Henzi Applied Behavioural Ecology and Ecosystem Research Unit, University of South Africa, Johannesburg, South Africa S. K. Maloney School of Anatomy, Physiology and Human Biology, University of Western Australia, Crawley, Australia