METABOLISM AND THERMOREGULATION IN THE LEVANT VOLE MICROTUS-GUENTHERI- THE ROLE OF PHOTOPERIODICITY

1. The populations of the Levant vole, Microtus guentheri, inhabiting the Mediterranean ecosystem of Israel, are marginal populations which seem to be well adapted to its long dry and warm season. The thermoreg ulatory and metabolic responses of the Levant voles of Israel to manip ulation of photoperiod were studied to assess the role of photoperiodi city in seasonal acclimatization. 2. Resting metabolic rate (RMR) and body temperature at various ambient temperatures, overall thermal cond uctance, nonshivering thermogenesis, gross energy and digestible energ y intake were measured in voles acclimated to long scotophase (8L:16D) and long photophase (16L:8D) at a constant ambient temperature of 25 +/- 1 degrees C. 3. This study revealed that acclimation to a long pho tophase resulted in a decreased RMR and minimal thermal conductance, b ut in a higher upper critical point of the thermoneutral zone, as well as higher gross energy and digestible energy intakes and in a higher body mass. 4. Therefore, we suggest that an increased photophase is an important environmental cue for summer acclimatization of the metabol ic and thermoregulatory systems in the Levant vole.