Daily rhythms of metabolic rates: role of chemical signals in coexistence of spiny mice of the genus Acomys

The common spiny mouse Acomys cahirinus and the golden spiny mouse A. russatus coexist in the extreme arid and hot parts of the Arava Rift Valley in Israel. The coexistence of these two species is through exclusion of A. russatus from nocturnal activity by A. cahirinus, which is nocturnal. An attempt was made to study the daily activity rhythm response of A. russatus to chemical signals released by A. cahirinus, in order to understand the mechanism of segregation. For this purpose oxygen consumption, V̇O₂, was studied in individuals of A. rassatus kept alone in a metabolic chamber in a constant ambient temperature of 32°C under two photoperiod regimes: 12L : 12D, and constant darkness (D:D). After three days of V̇O₂ recording under these conditions, chemical signals released from A. cahirinus were passed through the metabolic chamber. This treatment caused a shift in the activity rhythm only of A. russatus kept at 12L:12D, white a decrease in V̇O₂ rates of A. russatus was noted in both groups. These results suggest that chemical signals released by A. cahirinus may play a role in shifting A. russatus toward its diurnal activity.