Data from: Individual differences in torpor expression in adult mice are related to relative birth weight

Daily torpor is a physiological adaptation in small mammals and birds, characterised by drastic reductions in metabolism and body temperature. Energy-constraining conditions, such as cold and starvation, are known to cause the expression of daily torpor. However, the reason for high degrees of inter- and intra- individual variation in torpor expression (TE) in similar situations is not clear. As littermates of altricial animals are exposed to an uneven allocation of maternal resources from conception to weaning, we tested whether early nutritional experiences have long-term effects on TE in adults. We used full-sibling littermates of laboratory mice that as adults were starved overnight to induce torpor. We measured body weight from birth until adulthood as an indicator of nutritional status, and calculated the relative body weight (RBW) as an indicator of the difference in nutritional status within a litter. After maturation, we subjected mice to five repeated torpor induction trials involving 24 hours of fasting and 5 days of recovery. Half of the female mice displayed great individual variation in TE, whereas male mice rarely exhibited daily torpor. In females, RBW at birth influenced TE, irrespective of body weight in adulthood; thus, female mice born with low RBWs displayed high TE in adulthood. In conclusion, we provide evidence that TE in mice differs among littermates, and that this variation is linked closely to heterogeneous nutritional experiences during the foetal period.

日常蛰伏（daily torpor）是小型哺乳类与鸟类的一种生理适应策略，其核心特征为代谢速率与体温的急剧下降。已知寒冷、饥饿等能量受限条件可诱发日常蛰伏的表达，但在相似环境下，个体间及个体内的蛰伏表达（TE）仍存在高度变异，其背后机制尚不明确。由于晚熟动物的同窝幼崽自受孕至断奶阶段，母源资源的分配存在不均现象，本研究旨在探讨早期营养经历是否会对成年个体的TE产生长期影响。实验选用实验室小鼠的全同胞同窝幼崽，待其成年后通过过夜禁食诱导蛰伏。研究人员以出生至成年阶段的体重变化作为营养状况的评估指标，并计算相对体重（RBW）以表征同窝个体间的营养状态差异。个体成熟后，对小鼠开展五次重复的蛰伏诱导实验，每次实验包含24小时禁食与5天的恢复期。实验结果显示：半数雌性小鼠的TE存在显著个体差异，而雄性小鼠极少表现出日常蛰伏；在雌性个体中，出生时的RBW会对TE产生影响，且该效应与成年体重无关——即出生时RBW较低的雌性小鼠，成年后会表现出更高的TE水平。综上，本研究证实小鼠的TE存在同窝间差异，且这种变异与胎儿期不均等的营养经历密切相关。