Pergamon 0031-9384(95)00126-3 Physiology & Behavior, Vol. 58, No. 4, pp. 775-778, 1995 Copyright © 1995 Elsevier Science Inc. Printed in the USA. All fights reserved 0031-9384/95 $9.50 + .00 Oxygen Consumption and Body Temperature Rhythms in the Golden Spiny Mouse: Responses to Changes in Day Length A. HAIM .1 AND N. ZISAPELt *Department of Biology, University of Haifa at Oranim, P.O. Kiryat Tivon 36006 and #Department of Neurobiochemistry, Tel Aviv University, Ramat Aviv, Tel Aviv 69978 Israel Received 8 August 1994 HA/M, A. AND N. ZISAPEL. Oxygen consumption and body temperature rhythms in the golden spiny mouse: Responses to changes in day length. PHYSIOL BEHAV 58(4) 775-778, 1995.--The golden spiny mouse Acomys russatus is a rock dwelling rodent which lives in extremely arid and hot habitats. In Israel it is nocturnal except in areas in which it coexists with the common spiny mouse A. cahirinus. In such places it is diurnal. The daily rhythms of body temperature (T b) and oxygen consumption (VO 2) were compared in mice acclimated to two different photoperiod regimes in the laboratory: 8L:16D (short day) and 16L:8D (long day) at a constant ambient temperature. The daily rhythms of VO 2 and of T b in A. russatus were found to differ greatly under long and short photoperiod. Both parameters peaked at lights-out under both photoperiod regimes. In short day acclimated mice the effect of transmitter implantation was also studied. VO 2 values at night were lower after implanting. The results of this study show that T b and VO 2 rhythms are altered by the lighting regimes. Seasonal acclimatization of thermoregulatory mechanisms in the golden spiny mouse are partly induced by changes in photoperiodicity. Photoperiod Rodents Daily rhythms Thermoregulation Seasonality Oxygen consumption Diurnal activity Nocturnal activity INTRODUCTION THE THERMOREGUL~.TORY responses of rodents to changes in photoperiod have been studied over two decades beginning with the study of Lynch (16). In many of these studies it was noted that acclimation to a short photoperiod induced an increase in heat production (for review see 13). It was therefore assumed that increase in scotophase could be used as a cue for winter acclimatization of therraoregulatory mechanisms (3,5-8). Re- cently, it was shown that in the Levant vole Microtus guentheri as well as in the common wood-mouse Apodemus sylvaticus acclimation to a long photophase increased resistance to high ambient temperatures (2,11) and therefore it could be assumed that increase in photoperiod in these Palaearctic species is an important cue for summer seasonal acclimatization of thermoreg- ulatory mechanisms. The golden spiny me,use Acomys russatus, an Arabo-Sinaitic species, (21) is distributed in the most extreme dry and hot parts of the Rift-Valley in Israel as well as in other xeric, rocky habitats in the Arabian region (12). In most parts of its distribu- tion area, this species coexists with the common spiny mouse Acomys cahirinus. The coexistance of these two species in the same habitat leads to temporal segregation in which A. cahirinus is nocturnal and A. russatus is diurnal. The removal of the former from the common habitat resulted in a shift of the latter into nocturnal activity (19). It was also noted that in individuals of A. russatus born in captivity and kept separately from A. cahirinus under controlled conditions (Ta = 28°C, 12L:12D), the daily rhythms of T b and VO 2 resemble those of a nocturnal species (4,17). However, A. russatus was found to be well adapted to diurnal activity compared with nocturnal A. cahirinus. These adaptations include very low resting metabolic rates--44% lower than ex- pected for its body mass according to allometric equations (5,15), a high value of the lower critical point (Tic) at an ambient temperature (Ta) of 33°C (7) and a high overall thermal conduc- tance (7,20). In addition it was shown that A. russatus has a very 1 To whom requests for reprints should be addressed. 775