Montgomerie Claire, Lian Marianne, Breed Greg, Keogh Mandy, Kielland Knut
Department of Biology and Wildlife, University of Alaska Fairbanks, 2090 Koyukuk Drive, Fairbanks, AK, 99775, USA.
Department of Forestry and Wildlife Management, Inland Norway University of Applied Sciences, 2480, Koppang, Norway.
J Comp Physiol B. 2025 May 7. doi: 10.1007/s00360-025-01617-0.
Cyclic changes in snowshoe hare (Lepus americanus) fecundity have been attributed to changes in winter forage availability and predation pressure. Disentangling how nutrition and predation pressure affect snowshoe hare physiology is complex. As an herbivore of the northern boreal forests, snowshoe hares cope with extreme seasonal changes in diet, ambient temperature, and energy demands. We examined seasonal variation in the body condition index, blood biomarkers indicative of nutritional status, and fecal cortisol metabolite concentrations, in snowshoe hares across five ecologically distinct times of year in relation to adult survival rates. Snowshoe hares sampled from a high-density population in northern Alaska during 2018 showed decreases in survival and in plasma concentrations of total protein (TP), blood urea nitrogen (BUN), hematocrit (Hct), Chloride (Cl) and glucose during March and October. Increased survival and concentrations of Cl, TP, BUN, Hct, sodium (Na) and glucose were observed during August. Decreases in mass and survival from August to October suggest limited forage. Increases in TP, BUN, Hct and glucose in December suggest higher metabolic turnover. Fecal cortisol concentrations were not significantly associated with seasonal nutritional condition. A two-fold increase in mean cortisol was observed during August, potentially associated with energetically costly processes such as increased movement and reproduction. This work provides seasonal observations of snowshoe hare plasma biochemical values (N = 164) indicative of nutritional status, and supports the idea of using a collective biomarker approach to advance our understanding of how seasonality may play a role in snowshoe hare physiology.
雪兔（美洲兔）繁殖力的周期性变化归因于冬季食物可获得性和捕食压力的变化。厘清营养和捕食压力如何影响雪兔生理机能是复杂的。作为北方针叶林的食草动物，雪兔要应对饮食、环境温度和能量需求方面的极端季节性变化。我们研究了在一年中五个生态不同时期的雪兔的身体状况指数、指示营养状况的血液生物标志物以及粪便皮质醇代谢物浓度的季节性变化，并将其与成年雪兔的存活率相关联。2018年从阿拉斯加北部高密度种群中采样的雪兔在3月和10月期间存活率下降，血浆中总蛋白（TP）、血尿素氮（BUN）、血细胞比容（Hct）、氯离子（Cl）和葡萄糖浓度也下降。8月观察到存活率以及Cl、TP、BUN、Hct、钠（Na）和葡萄糖浓度增加。8月至10月体重和存活率下降表明食物有限。12月TP、BUN、Hct和葡萄糖增加表明代谢周转率更高。粪便皮质醇浓度与季节性营养状况没有显著关联。8月观察到平均皮质醇增加了两倍，这可能与诸如活动增加和繁殖等能量消耗大的过程有关。这项工作提供了雪兔血浆生化值（N = 164）的季节性观察结果，这些值指示了营养状况，并支持使用综合生物标志物方法来推进我们对季节性如何在雪兔生理机能中发挥作用的理解。
