Unpredictable deprivation of water increases the probability of torpor in the Syrian hamster.

The effect of unpredictable water deprivation on hibernation was investigated in the Syrian hamster under natural photoperiod and temperature. Based on our previous findings, we hypothesized that 1) deprivation of water caused testicular regression, 2) the magnitude of regression depended on unpredictability of water deprivation, 3) unpredictable deprivation of water on 50% of the days of the experimental period causes more testicular regression for animals than regular deprivation every other day, even if the total lengths were the same for the two treatments, and thus, 4) unpredictable deprivation of water induces hibernation more readily than regular deprivation or no deprivation. The results showed that the animals with the random and unpredictable deprivation a) started hibernation earlier, b) had a higher chance of being in torpor at the end of hibernation season, c) spent more time in torpor during hibernation than those animals which were deprived of water on a regular basis or the control, non-deprived animals. These findings supported our working hypothesis.