Daily rhythms of body temperature in Acomys russatus: the response to chemical signals released by Acomys cahirinus.

Two species of spiny mice of the genus Acomys--the golden spiny A. russatus and the common spiny A. cahirinus--are sympatric in the arid and hot parts of the Rift Valley in Israel. The coexistence of these two species is due to exclusion of A. russatus mice by A. cahirinus mice from nocturnal activity. The aim of this research was to study if odor signals released by A. cahirinus mice can play a role in the exclusion of A. russatus mice. A. russatus mice with an implanted transmitter recording body temperature (Tb) were kept alone in a metabolic chamber under constant conditions of ambient temperature (27 degrees C) and photoperiod (12 h light:12 h dark). After 5 days of recording, chemical signals from an A. cahirinus mouse were added through the air tube going into the metabolic chamber of the A. russatus mice. This treatment caused a shift of approximately 2 h in Tb daily rhythm of the naive tested A. russatus mice, whereas no shift was observed in A. russatus mice that had been kept in the same room with the A. cahirinus mouse before measurements. These results strongly support the idea that chemical signals released by A. cahirinus mice can entrain the Tb rhythms of A. russatus mice. Therefore, it may be assumed that the exclusion of A. russatus mice from nocturnal activity by A. cahirinus mice could be achieved through the odor released by the latter.