Data from: Winter corticosterone and body condition predict subsequent breeding investment in nonmigratory bird
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Reproduction is an energetically-demanding life history stage that requires costly physiological and behavioral changes, yet some individuals will invest more into reproduction and breed more successfully than others. To understand variation in reproductive investment, previous studies have evaluated factors during breeding, but conditions outside of this life history stage may also play a role. Using a free-ranging population of black-capped chickadees (Poecile atricapillus), we assessed the repeatability of plastic traits relating to energetic condition (circulating initial corticosterone concentrations and body condition) during the non-breeding season and evaluated whether these traits predicted reproductive investment in the subsequent breeding season. We found that initial corticosterone concentrations and an index of body condition, but not fat score, were moderately repeatable over a one-week period in winter. This trait repeatability supports the interpretation that among-individual variation in these phenotypic traits could reflect an intrinsic strategy to cope with challenging conditions across life history stages. We found that females with larger fat reserves during winter laid eggs sooner and tended to spend more time incubating their eggs and feeding their offspring. In contrast, we found that females with higher residual body mass delayed breeding, after controlling for the relationship between fat score and timing of breeding. Additionally, females with higher initial corticosterone in winter laid lighter eggs. Our findings suggest that conditions experienced outside of the breeding season may be important factors explaining variation in reproductive investment.
繁殖是一项高能量需求的生活史阶段，伴随高昂的生理与行为代价，但不同个体间的繁殖投入水平与繁殖成功率存在显著差异。为解析繁殖投入的变异机制，既往研究多聚焦繁殖期内的影响因子，而该生活史阶段之外的环境条件或许同样发挥重要作用。本研究以黑头山雀（Poecile atricapillus）的野生种群为研究对象，于非繁殖期测定了与能量状态相关的可塑性性状的重复力，包括循环初始皮质酮（corticosterone）浓度与身体状况，并评估了这些性状能否预测后续繁殖期的繁殖投入。研究发现，冬季一周内，初始皮质酮浓度与身体状况指数具有中等程度的重复力，但脂肪评分无此特征。该性状的重复力特征表明，这些表型性状的个体间差异，可能反映了一种用于应对不同生活史阶段挑战的内在策略。研究显示，冬季脂肪储备量更高的雌性个体产卵时间更早，且往往会花费更多时间进行卵孵化与幼鸟育雏。与之相反，在控制脂肪评分与繁殖时间的相关性后，本研究发现体质量残差更高的雌性个体繁殖时间更晚。此外，冬季初始皮质酮水平更高的雌性个体所产的卵重量更轻。本研究结果表明，繁殖期外经历的环境条件，或许是解释繁殖投入变异的重要影响因子。
