Fasting triggers hypothermia, and ambient temperature modulates its depth in Japanese quail Coturnix japonica Miriam Ben-Hamo a, ⁎, Berry Pinshow a , Marshall D. McCue a , Scott R. McWilliams b , Ulf Bauchinger a,b a Mitrani Department of Desert Ecology, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, 84990 Midreshet Ben-Gurion, Israel b Department Natural Resources Science, 105 Coastal Institute in Kingston, University of Rhode Island, Kingston, RI 02881, USA abstract article info Article history: Received 25 November 2009 Received in revised form 30 December 2009 Accepted 31 December 2009 Available online xxxx Keywords: Aves Body mass Body temperature Energetics Homeothermy Metabolic rate Temperature regulation We tested three hypotheses regarding the cues that elicit facultative hypothermia in Japanese quail (Coturnix japonica): H 1 ) Ambient temperature (T a ), alone, influences the onset and depth of hypothermia; H 2 ) Fasting, alone, influences the onset and depth of hypothermia; H 3 ) T a acts synergistically with fasting to shape the use of hypothermia. Eight quail were maintained within their thermoneutral zone (TNZ) at 32.6 ± 0.2 °C, and eight below their lower critical temperature (T lc ) at 12.7 ± 3.0 °C. All quail entered hypothermia upon food deprivation, even quail kept within their TNZ. Body temperature (T b ) decreased more (38.36 ± 0.53 °C vs. 39.57 ± 0.57 °C), body mass (m b ) loss was greater (21.0 ± 7.20 g vs.12.8 ± 2.62 g), and the energy saved by using hypothermia was greater (25.18–45.01% vs. 7.98–28.06%) in low the T a treatment than in TNZ treatment. Interestingly, the depth of hypothermia was positively correlated with m b loss in the low T a treatment, but not in TNZ treatment. Our data support H 3 , that both thermoregulatory costs and body energy reserves are proximate cues for entry into hypothermia in quail. This outcome is not surprising below the T lc . However, the quail kept at their TNZ also responded to food deprivation by entering hypothermia with no apparent dependence on m b loss. Therefore inputs, other than thermoregulatory costs and body condition, must serve as cues to enter hypothermia. Consequently, we address the role that tissue sparing may play in the physiological ‘decision’ to employ hypothermia. © 2010 Elsevier Inc. All rights reserved. 1. Introduction Facultative hypothermia, the down regulation of metabolic rates and body temperature (T b ) below normorthermic levels, is a wide- spread physiological mechanism used by birds to save energy (McKechnie and Lovegrove, 2002; Schleucher, 2004). Some birds use hypothermia on a regular basis, even daily, to reduce energy ex- penditure required for thermoregulation despite their nutritional status, while other species enter hypothermia only in response to food deprivation (Graf et al., 1989; Hohtola et al., 1991; Schleucher, 2001; McKechnie and Lovegrove, 2002). Although hypothermia has been shown to occur in many avian species (McKechnie and Lovegrove, 2002), the cues eliciting this phenomenon are not yet well understood. Numerous researchers found that the decrease in T b during hypothermia is dependent on ambient temperature (T a ) and therefore concluded that hypothermia is a mechanism for reducing energy expenditure necessary for thermoregulating in the cold (Haftorn, 1972; Chaplin, 1976; Reinertsen and Haftorn, 1983; Reinertsen and Haftorn, 1986; Merola-Zwartjes, 1998; Brigham et al., 2000; Merola- Zwartjes and Ligon, 2000; Dolby et al., 2004; Fletcher et al., 2004; Cooper and Gessaman, 2005). Their assumption was that at low T a ,a decrease in T b will lower the T b –T a difference and decrease the rate of heat loss, thereby reducing the demand for metabolic heat production (Kleiber, 1975; McNab, 2002; Welton et al., 2002). However, in eight passerine species, no relationship between T a and the depth of hypo- thermia (i.e., the decrease in T b during the rest-phase compared to nighttime normothermia) was found within a range of temperatures below their lower critical temperatures (T lc )(Steen, 1958; Cooper and Gessaman, 2005). Furthermore, in 17 species of hummingbirds, in Japanese quail (Coturnix japonica) and in red-headed finches (Amadina erythrocephala), T a was not found to trigger hypothermia (Kruger et al., 1982; Hohtola et al., 1991; McKechnie and Lovegrove, 2003). Thus, T a alone may not fully explain the use of hypothermia. Some cases of decreased T b in birds have been linked to reduced food availability or depletion of body energy reserves. With respect to the latter, food-restricted rock pigeons (Columba livia) and Japanese quail used shallow nocturnal hypothermia (Graf et al., 1989; Hohtola et al., 1991), and it has been found that the depth of hypothermia is proportional to changes in body energy reserves (Reinertsen and Haftorn, 1983; Reinertsen and Haftorn, 1986; Cooper and Gessaman, 2005). For example, in Japanese quail, continuous fasting induced progressively deeper nocturnal hypothermia (Laurila and Hohtola, 2005). A decline in energy reserves is thus followed by enhanced Comparative Biochemistry and Physiology, Part A xxx (2010) xxx–xxx ⁎ Corresponding author. Tel.: +972 86596773; fax: +972 86596772. E-mail addresses: miriammi@bgu.ac.il (M. Ben-Hamo), pinshow@bgu.ac.il (B. Pinshow), mmccue@bgu.ac.il (M.D. McCue), srmcwilliams@uri.edu (S.R. McWilliams), ulf@etal.uri.edu (U. Bauchinger). CBA-08883; No of Pages 8 1095-6433/$ – see front matter © 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.cbpa.2009.12.020 Contents lists available at ScienceDirect Comparative Biochemistry and Physiology, Part A journal homepage: www.elsevier.com/locate/cbpa ARTICLE IN PRESS Please cite this article as: Ben-Hamo, M., et al., Fasting triggers hypothermia, and ambient temperature modulates its depth in Japanese quail Coturnix japonica, Comp. Biochem. Physiol. A (2010), doi:10.1016/j.cbpa.2009.12.020