The theory of delayed life history effects assumes that phenotype of adult individual results from environmental conditions experienced at birth and as juvenile. In seasonal environments, being born late in the reproductive season affects timing of puberty, body condition, longevity, and fitness. We hypothesized that late-born individuals are more prone to respond to short photoperiod (SP) than early born ones. We used Siberian hamsters Phodopus sungorus, a model species characterized by high polymorphism of winter phenotype. We experimentally distinguished the effect of litter order (first or third) from the effect of exposure to long photoperiod (LP) before winter (3 months or 5 months) by manipulating the duration of LP acclimation in both litters. We predicted that, irrespective of the litter order, individuals exposed to long photoperiod for a short time have less time to gather energy resources and consequently are more prone to developing energy-conserving phenotypes. To assess effect of litter order, duration of acclimation to long days, and phenotype on basal cost of living we measured basal metabolic rate (BMR) of hamsters. Individuals born in third litters had faster growth rates and were bigger than individuals from first litters, but these differences vanished before transfer to SP. Litter order or duration of LP acclimation had no effects on torpor use or seasonal body mass changes, but prolonged acclimation to LP inhibited winter molting both in first and third litters. Moreover, individuals that did not molt had significantly higher BMR in SP than those which molted to white fur. Although one phenotype usually predominated within a litter, littermates were often heterogeneous. We also found that over 10% of individuals presented late response to short photoperiod. Our data indicate that duration of postnatal exposure to LP may define propensity to photoresponsiveness, regardless of the litter in which animal was born. Existence of littermates presenting different phenotypes suggests a prudent reproductive strategy of investing into offspring of varied phenotypes, that might be favored depending on environmental conditions. This strategy could have evolved in response to living in stochastic environment.

中文翻译：

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西伯利亚仓鼠冬季表型的多态性：连续产仔的光响应性没有差异，但长期适应长光周期会抑制冬季蜕皮

延迟生活史效应理论假设成年个体的表型是由出生时和青少年时期经历的环境条件造成的。在季节性环境中，生育季节晚出生会影响青春期时间、身体状况、寿命和健康。我们假设晚出生的个体比早出生的个体更容易对短光周期（SP）做出反应。我们使用西伯利亚仓鼠Phodopus sungorus，这是一种具有冬季表型高度多态性特征的模型物种。我们通过控制两窝幼仔的 LP 适应持续时间，通过实验区分了幼仔顺序（第一或第三）的影响与冬季前（3 个月或 5 个月）暴露于长光周期 (LP) 的影响。我们预测，无论窝序如何，短时间暴露于长光周期的个体收集能量的时间较少，因此更容易形成节能表型。为了评估窝序、适应长日照的持续时间和表型对基础生活成本的影响，我们测量了仓鼠的基础代谢率 (BMR)。第三窝出生的个体比第一窝出生的个体生长速度更快，体型更大，但这些差异在转移到 SP 之前就消失了。LP 适应的窝顺序或持续时间对麻木使用或季节性体重变化没有影响，但长时间的 LP 适应抑制了第一窝和第三窝的冬季蜕皮。此外，没有蜕皮的个体的 SP 中 BMR 显着高于那些蜕皮为白色皮毛的个体。尽管同窝动物中通常有一种表型占主导地位，但同窝动物往往是异质的。我们还发现超过 10% 的人对短光周期反应迟缓。我们的数据表明，无论动物出生在哪一窝，出生后暴露于 LP 的持续时间可能决定光响应倾向。表现出不同表型的同窝仔猪的存在表明，投资于不同表型的后代的谨慎繁殖策略可能会根据环境条件而受到青睐。这种策略可能是为了适应随机环境中的生活而进化的。