Przybylska-Piech Anna S, Wojciechowski Michał S, Jefimow Małgorzata
Department of Vertebrate Zoology and Ecology, Nicolaus Copernicus University, Toruń, Poland.
Department of Animal Physiology and Neurobiology, Nicolaus Copernicus University, Toruń, Poland.
Front Zool. 2021 Mar 18;18(1):11. doi: 10.1186/s12983-021-00391-3.
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.
延迟生活史效应理论认为，成年个体的表型源于出生时和幼年时期所经历的环境条件。在季节性环境中，繁殖季节后期出生会影响青春期时间、身体状况、寿命和适应性。我们假设晚出生个体比早出生个体对短光照周期（SP）更易产生反应。我们使用了以冬季表型高度多态性为特征的模式物种——西伯利亚仓鼠（Phodopus sungorus）。通过控制两窝仓鼠的长光照周期（LP）适应时长，我们实验性地区分了出生顺序（第一胎或第三胎）的影响与冬季前暴露于长光照周期（3个月或5个月）的影响。我们预测，无论出生顺序如何，短时间暴露于长光照周期的个体积累能量资源的时间较少，因此更易形成节能表型。为了评估出生顺序、长日照适应时长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）。
第三窝出生的个体生长速度更快，体型比第一窝出生的个体更大，但这些差异在转移到短光照周期之前就消失了。出生顺序或长光照周期适应时长对蛰伏行为或季节性体重变化没有影响，但长时间适应长光照周期会抑制第一窝和第三窝仓鼠在冬季的换毛。此外，未换毛的个体在短光照周期下的基础代谢率显著高于换毛为白色皮毛的个体。虽然通常一窝内一种表型占主导，但同窝幼崽往往具有异质性。我们还发现，超过10%的个体对短光照周期呈现延迟反应。
我们的数据表明，出生后暴露于长光照周期的时长可能决定光反应倾向，而与动物出生的窝次无关。存在呈现不同表型的同窝幼崽表明了一种谨慎的繁殖策略，即投资于具有不同表型的后代，这可能根据环境条件而受到青睐。这种策略可能是为了应对随机环境而进化出来的。
