Effects of photoperiod and temperature on body weight, food intake, food storage, and pelage color in the Djungarian hamster, Phodopus sungorus

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Abstract
Body weight, food intake, pelage color, and testis size in Djungarian hamsters are known to show annual cycles. To analyze the environmental factors that control the annual cycle of these physiological parameters, we performed an experiment with four combinations of photoperiods and temperatures (long photoperiod and high temperature, long photoperiod and low temperature, short photoperiod and high temperature, and short photoperiod and low temperature). Short photoperiod (8L16D) induced a decrease in body weight and testis size and an increase in the ratio of food storage behavior, total hair length, and the length of white distal region of hairs (a quantitative measure of pelage color) under both low (7°C) and high (25°C) temperatures. Long photoperiod (16L8D) induced the opposite effects. Low temperature induced an increase in the amount of food intake under both long and short photoperiods. under high temperature, food intake was greater in long photoperiod than in short photoperiod. Thus, we conclude that the main environmental factor for regulating annual cycles of various parameters in the Djungarian hamster is photoperiod. Photoperiodically regulated food storage behavior seems to have an important role for the strict control of body weight and food intake.