Thermoregulatory responses to manipulations of photoperiod in wood mice Apodemus sylvaticus from high latitudes (57°N)

1. 1. The thermoregulatory responses to manipulations of photoperiod in wood mice (Apodemus sylvaticus), which were drawn from a population living at a high latitude (57°N) were studied. 2. 2. Mice captured in spring were acclimated to two different photoperiod regimes 16L:8D and 8L:16D at a constant ambient temperature of 24°C, for 3 weeks. 3. 3. Daily rhythms of body temperature, oxygen consumption and body temperature at various ambient temperatures, nonshivering thermogenesis (the response to a noradrenaline injection) and body mass were measured. Minimal overall thermal conductance was calculated for both groups. 4. 4. Acclimation to long photophase increased the thermoregulatory abilities at relatively high ambient temperatures while that of long-scotophase increased thermoregulatory abilities at low ambient temperatures. 5. 5. Changes in photoperiod may therefore be used as cues for seasonal acclimatization of thermoregulatory mechanisms in this population of wood mice.