The effects of day length and ambient temperature on the growth and structure of adipose tissue and other organs in the dwarf hamster <i>P. campbelli</i>

The effects of photoperiod and ambient temperature on body mass and composition were studied in Phodopus campbelli. Adult hamsters were studied for 102 d around the mid-winter solstice (1991-1994), under four different combinations of photoperiod and environmental temperature, 24 °C 16 h light/8 h dark, WLD ('simulated summer'), 24 °C (8 h light/16 h dark, WSD, cold 10 °C 16 h light/8 h dark, CLD, 10 °C 8 h light/16 h dark, CSD ('simulated winter'). Specimens were caged individually, with rat chow and water available ad lib. Body mass and food intake were measured weekly. At the end of the experimental period, the mass and composition of 15 adipose depots, mass of the major organs, the colour, extractable lipid and hair length of the pelt were measured. Females ate relatively more food than their male counterparts. Hamsters on CLD ate the most, followed by CSD hamsters, those on WSD and WLD ate significantly less. Males on short photoperiod lost most weight, due mainly to depletion of adipose tissue. In both long day environments, the males maintained their body mass. Maximum decrease in lipid content and increase in protein content occurred in the adipose tissue of hamsters on CSD, especially in brown adipose tissue. The pelt became light grey in 'winter', probably the best camouflage for an arid climate. Changes in extractable lipid may be related to insulation: the sparser the hairs, the more lipid recovered from them. I conclude that photoperiod was the dominant influence on body size and lipid stores, but temperature interacted to affect many of the features studied. The hamsters' appetite adjusted to maintain body mass and composition. Photoperiod is the more reliable cue than weather for wild Phodopus for the physiological adaptations required for surviving in the cold Mongolian desert