Energy budget during four successive bouts of lactation in striped hamsters exposed to decreases in ambient temperature

A prediction of the seasonal investment hypothesis is that overall energy investment needs to be greater for young being produced at colder temperatures. Then, that energy cost is lower as temperature becomes warmer. To evaluate this assumption, I performed a series of measures of food intake and reproductive output throughout four successive bouts of lactation in striped hamsters (Cricetulus barabensis) exposed to a constant warm temperature (Warm, 21 °C) or exposed to consecutive decreases in ambient temperatures from warm to cold (Warm-Cold, 30-0 °C). Warm hamsters showed similar asymptotic food intake, litter size and mass over the course of four successive bouts of lactation. Warm-Cold females consumed more food, but raised lighter litters during the third bout than first bout of lactation. Ambient temperatures had significant effects on energy budget and reproductive output, by which resting metabolic rate, nonshivering thermogenesis and activity of cytochrome c oxidase (EC 1.9.3.1) of brown adipose tissue were increased, but reproductive output was decreased with declines of temperatures. These findings suggest that a trade-off occurs between different components of energy expenditure during the successive course of four bouts of lactation. Seasonal hamsters decrease their reproductive output, but increase the energy spent on thermogenesis as the ambient temperature becomes colder. It may also indicate that temperature has a direct effect on metabolism, leading to an increase in overall energy expenditure at lower temperatures.