Gender markedly modulates behavioral thermoregulation in a non-human primate species, the mouse lemur (Microcebus murinus) J. Terrien ⁎, M. Perret, F. Aujard Mécanismes Adaptatifs et Évolution, UMR CNRS/MNHN 7179, 1 avenue du Petit Château, 91800 Brunoy, France abstract article info Article history: Received 6 October 2009 Received in revised form 28 May 2010 Accepted 26 July 2010 Keywords: Behavioral adjustment Core temperature Ambient temperature Aging Sex Season Non-human primate Age and gender are known to significantly modulate thermoregulatory capacities in mammals, suggesting strong impacts on behavioral adjustments, which are used to minimize the energy costs of thermoregulation. We tested the effects of sex and age on spontaneous choice of ambient temperature (Ta) in a non-human primate species, the mouse lemur (Microcebus murinus). The animals acclimated to both winter and summer photoperiods, two seasons significantly modifying thermoregulation function, were experimented in a thermal gradient device. During winter, adult males did not show preference for warm Tas whereas old males did. In contrast, female mouse lemurs of both age categories exhibited great preferences for warm Tas. Acclimation to summer revealed that males selected colder Ta for the day than during the night. Such behavior did not exist in females. Old females explored and selected warmer nests than adult ones. This study raised novel issues on the effect of gender on thermoregulatory capacities in the mouse lemur. Females probably use behavioral adjustments to limit energy expenditure and might prefer to preserve energy for maternal investment by anticipation of and during the breeding season. Further experiments focusing on female thermoregulatory capacities are needed to better understand the energy challenge that may occur during winter and summer in female mouse lemurs, and whether this trade-off changes during aging. © 2010 Elsevier Inc. All rights reserved. 1. Introduction There are compelling evidences suggesting that gender influences thermoregulatory capacities [1–3]. For example, in rodents, adult females differ from males in their thermogenic response and exhibit greater capacities for cold-induced involvement of heat production [4,5]. Such gender effect would be preserved during aging [6–9], old females exhibiting greater capacities for cold-induced thermogenesis than old males. In parallel to autonomic capacities, mammals have developed behavioral strategies to reduce their metabolic rate [10–12] and thus limit the energy costs of thermoregulation. Regarding the age effect on physiological thermoregulatory capacities, behavioral adjust- ments may also play a compensatory role for age-related autonomic deficiencies. Regarding this, thermoregulatory behaviors might strongly differ between males and females, and furthermore between adult and aged individuals. For a better understanding of gender impact on age-related deterioration in thermoregulatory behaviors, we investigated spontaneous temperature selection in a thermal gradient in a non-human primate, the grey mouse lemur (Microcebus murinus). In this Malagasy photoperiod-dependent primate, long day lengths (i.e. N 12 h/day) enhance behavioral and physiological functions, thus triggering sexual activation and body mass loss [13]. In contrast, exposure to winter-like day length shorter than 12 h induces total gonadal regression, reduction of physiological and behavioral activi- ties leading to fattening [14]. Such adjustments to seasonal variations imply strong modulations in many of biological functions, especially energy metabolism and thermoregulatory capacities [13–15]. Daily rhythmicity of core temperature (Tc) has been well described in mouse lemurs [16] and there are many evidences for strong interactions between the daily rhythm of Tc and photoperiod [15], ambient temperature [13,17–19], food availability [17,20] and social factors [17]. The mouse lemur exhibits thermoregulatory behaviors that strongly differ between males and females, in order to reduce energy costs of thermoregulation [21]. In fact, mouse lemurs may regroup in nests during their diurnal sleeping periods, thus promoting gregarism behaviors in buffered nests [22]. During winter, gender- mixed groups can be formed whereas males are essentially solitary during summer [23–25]. Thus, gregarism appears as a main behavioral adjustment in female mouse lemurs as compared to males. In this species, which mean life span in captivity is about 8 years [26], aging is associated with a decrease in amplitude of the seasonal variations in body mass, gonadal hormones [27], melatonin [28], and DHEA-S [29]. Studies investigating age effects on daily Tc rhythm did not show Physiology & Behavior 101 (2010) 469–473 ⁎ Corresponding author. Tel.: +33 1 60 47 92 00; fax: +33 1 69 24 99 61. E-mail address: jeremy.terrien@hotmail.fr (J. Terrien). 0031-9384/$ – see front matter © 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.physbeh.2010.07.012 Contents lists available at ScienceDirect Physiology & Behavior journal homepage: www.elsevier.com/locate/phb