Costanzo Jon P, Dinkelacker Stephen A, Iverson John B, Lee Richard E
Department of Zoology, Miami University, Oxford, OH 45056, USA.
Physiol Biochem Zool. 2004 Jan-Feb;77(1):74-99. doi: 10.1086/378141.
We integrated field and laboratory studies in an investigation of water balance, energy use, and mechanisms of cold-hardiness in hatchling painted turtles (Chrysemys picta) indigenous to west-central Nebraska (Chrysemys picta bellii) and northern Indiana (Chrysemys picta marginata) during the winters of 1999-2000 and 2000-2001. We examined 184 nests, 80 of which provided the hatchlings (n=580) and/or samples of soil used in laboratory analyses. Whereas winter 1999-2000 was relatively dry and mild, the following winter was wet and cold; serendipitously, the contrast illuminated a marked plasticity in physiological response to environmental stress. Physiological and cold-hardiness responses of turtles also varied between study locales, largely owing to differences in precipitation and edaphics and the lower prevailing and minimum nest temperatures (to -13.2 degrees C) encountered by Nebraska turtles. In Nebraska, winter mortality occurred within 12.5% (1999-2000) and 42.3% (2000-2001) of the sampled nests; no turtles died in the Indiana nests. Laboratory studies of the mechanisms of cold-hardiness used by hatchling C. picta showed that resistance to inoculative freezing and capacity for freeze tolerance increased as winter approached. However, the level of inoculation resistance strongly depended on the physical characteristics of nest soil, as well as its moisture content, which varied seasonally. Risk of inoculative freezing (and mortality) was greatest in midwinter when nest temperatures were lowest and soil moisture and activity of constituent organic ice nuclei were highest. Water balance in overwintering hatchlings was closely linked to dynamics of precipitation and soil moisture, whereas energy use and the size of the energy reserve available to hatchlings in spring depended on the winter thermal regime. Acute chilling resulted in hyperglycemia and hyperlactemia, which persisted throughout winter; this response may be cryoprotective. Some physiological characteristics and cold-hardiness attributes varied between years, between study sites, among nests at the same site, and among siblings sharing nests. Such variation may reflect adaptive phenotypic plasticity, maternal or paternal influence on an individual's response to environmental challenge, or a combination of these factors. Some evidence suggests that life-history traits, such as clutch size and body size, have been shaped by constraints imposed by the harsh winter environment.
在1999 - 2000年和2000 - 2001年冬季，我们结合了野外和实验室研究，对内布拉斯加州中西部（贝尔氏彩龟）和印第安纳州北部（缘彩龟）原产的孵化期彩龟的水平衡、能量利用及抗寒机制进行了调查。我们检查了184个巢穴，其中80个巢穴为实验室分析提供了幼龟（n = 580）和/或土壤样本。1999 - 2000年冬季相对干燥温和，而次年冬季则潮湿寒冷；巧合的是，这种对比凸显了生理反应对环境压力的显著可塑性。龟的生理和抗寒反应在不同研究地点之间也存在差异，这主要归因于降水量、土壤性质的差异，以及内布拉斯加州的龟所经历的较低的普遍温度和最低巢穴温度（低至 - 13.2摄氏度）。在内布拉斯加州，冬季死亡率在抽样巢穴中分别为12.5%（1999 - 2000年）和42.3%（2000 - 2001年）；印第安纳州的巢穴中没有龟死亡。对孵化期彩龟抗寒机制的实验室研究表明，随着冬季临近，对接种性冷冻的抵抗力和耐冻能力增强。然而，接种抗性水平很大程度上取决于巢穴土壤的物理特性及其含水量，而含水量会随季节变化。接种性冷冻（及死亡）风险在冬季中期最大，此时巢穴温度最低，土壤湿度和组成有机冰核的活性最高。越冬幼龟的水平衡与降水和土壤湿度动态密切相关，而能量利用以及春季幼龟可用能量储备的大小则取决于冬季热状况。急性低温导致高血糖和高乳酸血症，这种情况在整个冬季持续存在；这种反应可能具有抗冻保护作用。一些生理特征和抗寒属性在年份之间、研究地点之间、同一地点的巢穴之间以及共享巢穴的兄弟姐妹之间存在差异。这种差异可能反映了适应性表型可塑性、亲本对个体应对环境挑战反应的影响，或这些因素的综合作用。一些证据表明，诸如窝卵数和体型等生活史特征受到了严酷冬季环境施加的限制的影响。
