Data from: Ecology of ontogenetic body-mass scaling of gill surface area in a freshwater crustacean

Several studies have documented ecological effects on intra- and interspecific body-size scaling of metabolic rate. However, little is known about how various ecological factors may affect the scaling of respiratory structures supporting oxygen uptake for metabolism. Our study is apparently the first to provide evidence for ecological effects on the scaling of a respiratory structure among conspecific populations of any animal. We compared the body-mass scaling of gill surface area (SA) among eight spring-dwelling populations of the amphipod crustacean Gammarus minus. Although gill SA scaling was not related to water temperature, conductivity or G. minus population density, it was significantly related to predation regime (and secondarily to pH). Body-mass scaling slopes for gill SA were significantly lower in four populations inhabiting springs with fish predators than for those in four springs without fish (based on comparing means of the population slopes, or slopes calculated from pooled raw data for each comparison group). As a result, gill SA was proportionately smaller in adult amphipods from fish vs. fishless springs. This scaling difference paralleled similar differences in the scaling exponents for the rates of growth and resting metabolic rate. We hypothesized that gill SA scaling is shallower in fish vs. fishless spring populations of G. minus because of effects of size-selective predation on size-specific growth and activity that in turn affect the scaling of oxygen demand and concomitantly the gill capacity (SA) for oxygen uptake. Although influential theory claims that metabolic scaling is constrained by internal body design, our study builds on previous work to show that the scaling of both metabolism and the respiratory structures supporting it may be ecologically sensitive and evolutionarily malleable.

多项研究已证实，生态因子会对代谢率的种内与种间体型缩放关系产生调控作用。然而，当前学界对于各类生态因子如何调控支撑代谢摄氧的呼吸结构的缩放关系，仍缺乏充分认知。本研究堪称首个在任意动物的同种种群间，为呼吸结构缩放的生态调控效应提供实证依据的学术工作。我们以端足类甲壳动物Gammarus minus的8个泉生种群为研究对象，比较了其鳃表面积（gill surface area, SA）与体重的缩放关系。研究结果显示，鳃表面积的缩放比例与水温、电导率或G. minus的种群密度并无显著关联，但却与捕食压力显著相关（次要关联因子为pH值）。相较于4处无鱼类捕食者的泉眼种群，栖息于4处有鱼类捕食者的泉眼的种群，其鳃表面积的体重缩放斜率显著更低——该结论可通过两种方式验证：一是比较各群的斜率均值，二是基于各组合并后的原始数据计算斜率。由此可见，相较于无鱼泉种群的成年端足类，有鱼泉种群的成年个体的鳃表面积相对更小。该缩放差异与生长速率及静息代谢率的缩放指数差异呈现出高度一致性。我们提出如下假说：Gammarus minus有鱼泉种群的鳃表面积缩放斜率较无鱼泉种群更为平缓，其原因在于体型选择性捕食对个体体型特异性生长与活动产生影响，进而改变了氧需求的缩放关系，同时也调控了用于摄氧的鳃表面积容量。尽管已有权威理论提出，代谢缩放受体内躯体设计的约束，但本研究依托前人工作进一步证实：代谢过程及其支撑呼吸结构的缩放关系均可受生态因子调控，且在进化层面具有可塑性。