Shortening photoperiod triggers seasonal adjustments like cessation of reproduction, molting and heterothermy. However there is a considerable among-individual variation in photoresponsiveness within one population. Although seasonal adjustments are considered beneficial to winter survival, and natural selection should favor the individuals responding to changes in photoperiod (responders), the phenotype non-responding to changes in day length is maintained in population. Assuming the same resource availability for both phenotypes which differ in strategy of winter survival, we hypothesized that they should differ in life history traits. To test this we compared reproductive traits of two extreme phenotypes of Siberian hamster Phodopus sungorus – responding and non-responding to seasonal changes in photoperiod. We bred individuals of the same phenotype and measured time to first parturition, time interval between litters, offspring body mass 3, 10 and 18 days after birth and their growth rate. We also analyzed nest-building behavior. Additionally, we estimated the correlation between reproduction, and basal metabolic rate (BMR) and oxidative status in both phenotypes to infer about the effect of reproductive output on future investments in somatic maintenance. Prior to reproduction responding individuals were smaller than non-responding ones, but this difference disappeared after reproduction. Responding pairs commenced breeding later than non-responding ones but there was no difference in time interval between consecutive litters. Responders delivered smaller offspring than non-responders and more out of responding individuals built the nest during winter than non-responding ones. Reproduction did not affect future investments in somatic maintenance. Phenotypes did not differ in BMR and oxidative status after reproduction. However, concentration of reactive oxygen metabolites (ROM) was highest in responding males, and biological antioxidant potential (BAP) was higher in males of both phenotypes than in females. Delayed breeding in responding Siberian hamsters and high ROM concentration in male responders support our hypothesis that differences in adjustment to winter result in different life history characteristics which may explain coexistence of both phenotypes in a population. We propose that polymorphism in photoresponsiveness may be beneficial in stochastic environment, where environmental conditions differ between winters. We suggest that non-responding phenotype may be particularly beneficial during mild winter, whereas responders would be favored under harsh conditions. Therefore, none of the phenotypes is impaired when compared to the other.

中文翻译：

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光反应性影响生活史特征，但不影响季节性啮齿动物的氧化状态

缩短光周期会引发季节性调整，例如停止繁殖、蜕皮和异温。然而，在一个群体内的光响应性存在相当大的个体差异。尽管季节性调整被认为有利于冬季生存，并且自然选择应该有利于对光周期变化做出反应的个体（响应者），但对日长变化无反应的表型在种群中仍然存在。假设冬季生存策略不同的两种表型的资源可用性相同，我们假设它们的生活史特征应该不同。为了测试这一点，我们比较了西伯利亚仓鼠 Phodopus sungorus 的两种极端表型的生殖特征——对光周期的季节性变化有反应和无反应。我们培育了具有相同表型的个体，并测量了第一次分娩的时间、窝之间的时间间隔、出生后 3、10 和 18 天的后代体重及其生长速度。我们还分析了筑巢行为。此外，我们估计了两种表型中繁殖、基础代谢率 (BMR) 和氧化状态之间的相关性，以推断繁殖输出对未来体细胞维持投资的影响。繁殖前有反应的个体比无反应的个体小，但这种差异在繁殖后消失了。有反应的对开始繁殖的时间比没有反应的晚，但连续窝之间的时间间隔没有差异。响应者比不响应者交付的后代更小，并且更多来自响应者在冬季建造的巢穴比不响应者更多。繁殖不影响未来对体细胞维持的投资。生殖后 BMR 和氧化状态的表型没有差异。然而，有反应的男性中活性氧代谢物 (ROM) 的浓度最高，两种表型的男性的生物抗氧化潜能 (BAP) 均高于女性。响应西伯利亚仓鼠的繁殖延迟和雄性响应者的高 ROM 浓度支持我们的假设，即对冬季的调整差异导致不同的生活史特征，这可能解释了种群中两种表型的共存。我们建议光响应性的多态性可能在随机环境中是有益的，其中冬季环境条件不同。我们建议在温和的冬季，无反应表型可能特别有益，而在恶劣条件下，反应者会受到青睐。因此，与其他表型相比，没有一种表型受损。