Body-temperature daily rhythms in Acomys cahirinus: Response to slope type and salinity

The common spiny mouse, Acomys cahirinus, in the Mediterranean system of Nahal Oren, Mount Carmel, inhabits the north- and south-facing slopes (NFS and SFS, respectively). In a comparative study of mice from the two slopes, body temperature (T_b) and daily rhythms were measured in mice exposed to increased salinity in their water source. For this purpose, mice were kept in outdoor cages during July-September. Mice were kept separately on a diet of soy beans while water was offered in the form of agar (2%) squares in which salinity was 0.9, 2.5, and 3.5% NaCl. Acclimation to each NaCl concentration lasted for at least two weeks. T_b was measured by inserting a thermocouple to a depth of 3 cm into the rectum of a mouse kept in a cotton bag for a period of 30 sec. T_b was recorded every 6 h over a period of 36 h. T_b values were lower in the SFS population compared with NSF, possibly due to lower metabolic rates. Increasing salinity, mainly from 2.5 to 3.5%, resulted in a higher T_b amplitude in mice from both slopes, possibly as a means to conserve water by increasing the T_b-ambient-temperature gradient.