Data from: Daily energy expenditure during lactation is strongly selected in a free-living mammal

1. Energy expenditure is a trait of central importance in ecological and evolutionary theory. We examined the correlates of, the strength of selection on, and the heritability of, daily energy expenditure (DEE; kJ/day) during lactation in free-ranging North American red squirrels (Tamiasciurus hudsonicus). 2. Over seven years, lactating squirrels with greater DEE had higher annual reproductive success (ARS; standardized selection gradient: β’ = 0.47; top 12% of published estimates). Surprisingly, positive fecundity selection on lactation DEE for increased ARS did not result because lactation DEE was correlated with typical measures of reproductive performance and/or investment. 3. We found no evidence of costs of elevated lactation DEE acting through female survival, subsequent year lactation DEE, or subsequent year reproduction. 4. Lactation DEE was not significantly repeatable and heritability was not significantly different from zero. 5. Elevated lactation DEE enhances ARS through a link between DEE and an unidentified measure of maternal or environmental quality, but there is limited evolutionary potential for lactation DEE to respond to our documented selection.

1. 能量消耗是生态学与进化学理论中核心重要的性状。我们针对自由生活的北美红松鼠（Tamiasciurus hudsonicus）哺乳期的每日能量消耗（daily energy expenditure, DEE；单位：千焦/日）的相关影响因素、选择作用强度以及遗传力展开了研究。2. 在为期7年的研究中，每日能量消耗更高的哺乳期雌性松鼠拥有更高的年度繁殖成功率（annual reproductive success, ARS；标准化选择梯度：β’ = 0.47，位列已发表相关估计值的前12%）。令人意外的是，针对哺乳期每日能量消耗的正向繁殖力选择并未提升年度繁殖成功率，这是因为哺乳期每日能量消耗与常规的繁殖表现或繁殖投入指标并无关联。3. 我们未发现因哺乳期每日能量消耗升高而产生的代价相关证据，这类代价可通过雌性存活率、次年哺乳期每日能量消耗或次年繁殖情况体现。4. 哺乳期每日能量消耗的重复性并不显著，且其遗传力与零并无显著差异。5. 哺乳期每日能量消耗升高可通过其与未明确的母体质量或环境质量指标之间的关联提升年度繁殖成功率，但哺乳期每日能量消耗针对本研究中观测到的选择作用所产生的进化潜力十分有限。