Comparison of the body temperature rhythms of diurnal and nocturnal rodents.

The daily rhythm of body temperature of six rodent species, three of them nocturnal (Rattus norvegicus, Mesocricetus auratus, and Meriones unguiculatus) and three diurnal (Octodon degus, Spermophilus tridecemlineatus, and S. richardsoni), was studied by telemetry under a 14L:10D light-dark cycle. Significant interspecies differences were found in the mean level (range: 36.0-37.4 degrees C), amplitude (range: 2.1 degrees-4.3 degrees C), robustness (range: 115-185 Qp), and acrophase (range: 8.5-16.0 hr) of the temperature rhythm. In addition, a positive correlation (r = 0.79) was found between body mass and robustness of the rhythm across species. However, the only consistent difference between the diurnal and nocturnal species was the acrophase, which occurred during the day in the diurnal species (range: 8.5-11.5 hr) and during the night in the nocturnal species (range: 13.5-16.0 hr).