Seasonal thermogenic acclimation of diurnally and nocturnally active desert spiny mice

Diurnally active golden spiny mice (Acomys russatus) and nocturnal common s piny mice (Acomys cahirinus) coexist in hot rocky deserts of Israel. Diurna l and nocturnal activities expose these species to different climatic condi tions. Nonshivering thermogenesis (NST) capacity of individuals of both spe cies immediately upon removal from the field exhibited seasonal changes, wi th no significant interspecific difference. Colony-reared mice of either sp ecies transferred in the laboratory from long to short photoperiod increase d NST capacity, though to a lesser extent than observed in the seasonal acc limatization. The underlying biochemical mechanisms of short photoperiod ac climation differed between the species. In both Cytochrome-c oxidase (Cox) activity was higher in short as compared to long photoperiod. In short-phot operiod-acclimated A. cahirinus uncoupling protein (UCP) content in brown a dipose tissue (BAT) was significantly higher than in long photoperiod, whil e in A. russatus there was no significant change. In A. russatus there was a significant increase in lipoprotein lipase (LPL) activity in BAT in short -photoperiod-acclimated individuals, while in A. cahirinus LPL activity was high under both acclimations. The low LPL activity in brown adipose tissue of desert-adapted A. russatus may facilitate lipid uptake in white adipose tissue, an advantage in desert conditions where food is scarce and irregul arly distributed in space and time.