TELEMETRIC OBSERVATIONS OF CIRCADIAN
RHYTHMS OF BODY TEMPERATURE IN SPINY
MICE (ACOMYS) LIVING IN THE JUDEAN
DESERT OF ISRAEL

R.ELVERT, G.HELDMAIER
Fachbereich Biologie / Zoologie, Philipps-Universität, D - 35032 Marburg

INTRODUCTION Trapping data have shown that the common spiny mouse (Acomys cahirinus, 30-45g) is active during the night, as are the most desert rodents, whereas the golden spiny mouse (Acomys russatus, 45-65g) is active during the day when coexisting in the same habitat (Shkolnik A 1971: Int J Biometeor, vol 15, number 2-4, 115). When A. cahirinus is absent from the habitat A. russatus shows a nocturnal pattern, too. We investigated body temperature rhythms (T_b) in a mixed population of both species in Ein Gedi Nature Reserve, Israel.

METHODS The habitat of the spiny mice in Ein Gedi is characterised by steep rocky mountain escarpments running parallel to the Dead Sea. Huge blocks alternate with small boulders. Shaded caves rises which are ideal living space for these mice. On a rocky hill slope of about 5000m² mice were trapped with 50 collapsible Sherman box traps and marked. Animals were implanted with temperature transmitters, developed by Oekokart E&V in Munich, into the abdominal cavity. With different fixed frequencies the transmitters sent signals in intervalls correlating with the T_b. Two antennas received the signals which were recorded by a tracking receiver (B+R, Freiburg) and transfered with an interface (Datalog, Moenchengladbach) to a computer. A special developed software checked the transmitters every 4min. Ambient temperatures (sun, shade, beneath a rock, in the measure box) were measured with thermocouples and stored in a data logger (AMR, Holzkirchen) parallel to the T_b. Solarpanels supplied the system with energy (Elvert et al 1996: Verh Dtsch Zool Ges, vol 89.1, 144).

RESULTS A.cahirinus showed an obvious rhythm of T_b, corresponding to a rhythm of a nocturnal animal in its natural habitat. Until now such circadian rhythms have only been shown under natural photoperiod in the laboratory (Kronfeld N et al 1994: Israel Journal of Zoology, vol 40, 177). In the activity phase during the night T_b rose to 37.5°C. During the day the temperature dropped to 34°C. The rhythm of T_b was detected in all four seasons. During the hot season T_b of A.russatus varied between 33 and 39.5°C, suggesting a bimodal temperature rhythm with maximal values in the morning and in the evening. In winter A.russatus showed no detectable rhythm in T_b. Body temperature varied between 36.5 and 37°C.

DISCUSSION These results point out that the activity during the day seems not connected with a phase shift of T_b to a rhythm of a typical diurnal animal. This might represent an adaptation to very high ambient temperatures.

With the supportment of the GIF (German Israelian Foundation)