Abstract. Standard metabolic rate is a major functional trait with large inter-individual variability in many groups of aquatic species. Here we present results of an experimental study to address variation in standard metabolic rates, over different scales of organisation and environments, within a specific group of aquatic macro-invertebrates (i.e. gammarid amphipods) that represent the primary consumers in detritus food webs. The study was carried out using flow-through microrespirometric techniques on male specimens of three gammarid species from freshwater, transitional water and marine ecosystems. We examined individual metabolic rate variations at three scales: (1) at the individual level, during an 8 h period of daylight; (2) at the within-population level, along body-size and body-condition gradients; (3) at the interspecific level, across species occurring in the field in the three different categories of aquatic ecosystems, from freshwater to marine. We show that standard metabolic rates vary significantly at all three scales examined, with the highest variation observed at the within-population level. Variation in individual standard metabolic rates during the daylight hours was generally low (coefficient of variation, CV ) and unrelated to time. The average within-population CV ranged between 30.0 % and 35.0 %, with body size representing a significant source of overall inter-individual variation in the three species and individual body condition exerting only a marginal influence. In all species, the allometric equations were not as steep as would be expected from the 3∕4 power law, with significant variation in mass-specific metabolic rates among populations. The population from the transitional water ecosystem had the highest mass-specific metabolic rates and the lowest within-population variation. In the gammarid species studied here, body-size-independent variations in standard individual metabolic rates were higher than those explained by allometric body size scaling, and the costs of adaptation to short-term periodic variations in water salinity in the studied ecosystems also seemed to represent a major source of variation.

中文翻译：

---

三种伽马科动物标准代谢率变异的组成部分

摘要。标准代谢率是一个主要的功能性状，在许多水生物种群体中具有很大的个体间变异性。在这里，我们展示了一项实验研究的结果，以解决代表碎屑食物网中主要消费者的特定水生大型无脊椎动物（即 gammarid 片脚类动物）在不同规模的组织和环境中标准代谢率的变化。该研究是使用流通式微呼吸测量技术对淡水、过渡水域和海洋生态系统中三种伽马科动物的雄性标本进行的。我们在三个尺度上检查了个体代谢率的变化：（1）在个体水平上，在 8 小时的日光期间；(2) 在种群内水平，沿着体型和体况梯度；(3) 在种间水平上，跨越从淡水到海洋的三个不同类别的水生生态系统中野外发生的物种。我们表明标准代谢率在所有三个检查的尺度上都有显着差异，在人群内观察到的变化最大。白天个体标准代谢率的变化通常很低（变异系数，CV）并且与时间无关。种群内的平均 CV 范围在 30.0% 和 35.0% 之间，体型代表了三个物种整体个体间变异的重要来源，而个体身体状况仅产生边际影响。在所有物种中，异速生长方程并不像 3∕4 幂定律所预期的那样陡峭，种群之间的质量特异性代谢率存在显着差异。来自过渡水生态系统的种群具有最高的质量特异性代谢率和最低的种群内变异。在这里研究的 gammarid 物种中，标准个体代谢率中与体型无关的变化高于异速生长的体型缩放所解释的变化，并且适应所研究生态系统中水盐度的短期周期性变化的成本似乎也代表变异的主要来源。