Data from: The active metabolic rate predicts a male spider’s proximity to females and expected fitness

Conspicuous traits, such as weaponry and body size, are often correlated with fitness. By contrast, we understand less about how inconspicuous physiological traits affect fitness. Not only is linking physiology directly to fitness a challenge, but in addition, behavioural studies most often focus on resting or basal metabolic rates, resulting in a poor understanding of how active metabolic rates affect fitness. Here we use the golden orb-web spider (Nephila plumipes), a species for which proximity to a female on the web predicts a male's paternity share, to examine the role of resting and active metabolic rates in fitness. Using a semi-natural experimental set-up, we show that males closer to a female have higher active metabolic rates than males further from females. This higher metabolic activity is paralleled by increased citrate synthase activity, suggesting greater mitochondrial densities. Our results link both higher active metabolic rates and increased citrate synthase activity with fitness. Coupled with the behaviour and life history of N. plumipes, these results provide insight into the evolution of physiological systems.诸如武器结构与体型尺寸这类显眼性状（conspicuous traits）通常与适合度（fitness）相关联。与之形成对比的是，学界对于不显眼的生理性状如何影响适合度的认知仍较为匮乏。不仅将生理机能直接与适合度建立关联是一项挑战，此外行为学研究大多聚焦于静息代谢率（resting metabolic rates）或基础代谢率（basal metabolic rates），导致学界对活动代谢率（active metabolic rates）如何影响适合度的认知同样不足。 本研究以金园蛛（golden orb-web spider，学名Nephila plumipes）为研究对象——该物种中，雄蛛在网上与雌蛛的亲近程度可预测其父权份额（paternity share）——以此探究静息代谢率与活动代谢率在适合度中的作用。通过半自然实验设置（semi-natural experimental set-up），我们发现：与雌蛛距离更近的雄蛛，其活动代谢率高于远离雌蛛的雄蛛。这种更高的代谢活性同时伴随柠檬酸合酶（citrate synthase）活性升高，提示线粒体密度（mitochondrial densities）更高。本研究结果将更高的活动代谢率与柠檬酸合酶活性升高均与适合度建立了关联。结合金园蛛的行为与生活史特征，本研究结果为生理系统的演化提供了新的认知视角。