Ecological separation by ecomorphology and swimming performance between two congeneric fish species

ABSTRACT The high diversity of freshwater fish species reflects a great morphological plasticity. Understanding the relationship between swimming capacity, morphology and habitat use may be important to predict the chances of finding a species at an anthropized environment. The swimming capacity and morphological aspects of two sympatric species of Characidium, and for which spatial segregation in different hydraulic habitats is known, were compared in this study. Twenty-one individuals of Characidium fasciatum Reinhardt, 1867 and 23 individuals of Characidium cf. zebra Eigenmann, 1909 were captured and used for the evaluation of the swimming capacity and ecomorphological attributes. The swimming capacity of each species was obtained by measuring critical and relative velocities. A total of 12 ecomorphological attributes correlated with habitat use and swimming characteristics were also compared. The Mann-Whitney mean test showed that the swimming capacity of C. fasciatum was greater than that of C. cf. zebra, and the standard length of the individuals explained 12.42% of the variation in their capacity to withstand water flow. Both species were morphologically distinct in the relative length of the caudal peduncle, ventral flattening index and the relative area of the pectoral fin. The relative area of the pectoral fin alone accounted for 16.71% of the differences in the ability to resist the water flow and which were not explained by body length. Our results showed that two species differed in the ecomorphological space and in their swimming capacity, supporting the hypothesis that the greater the hydrodynamism, the better a fish is able to withstand the water flow, and that this capacity is correlated with the morphological characteristics linked to the swimming activity of the fish.

摘要 淡水鱼类物种的高度多样性反映了其极强的形态可塑性。明晰游泳能力、形态特征与栖息地利用之间的关联，对于预测物种在人为干扰环境中的存续概率具有重要意义。本研究针对两种同域分布的裸脂鲤属（Characidium）鱼类——已知其在不同水力生境中存在空间分隔——比较了二者的游泳能力与形态学特征。本研究共捕获带纹裸脂鲤（Characidium fasciatum Reinhardt, 1867）21尾、疑似斑马裸脂鲤（Characidium cf. zebra Eigenmann, 1909）23尾，用于评估其游泳能力与生态形态学指标。通过测量临界流速与相对流速，获取了各物种的游泳能力数据；同时对比了12项与栖息地利用及游泳特性相关的生态形态学指标。曼-惠特尼均值检验结果显示，带纹裸脂鲤的游泳能力优于疑似斑马裸脂鲤；个体的标准体长可解释12.42%的鱼类抗水流能力变异。两种鱼类在尾柄相对长度、腹面扁平指数以及胸鳍相对面积上存在显著形态分化。其中仅胸鳍相对面积即可解释16.71%的、与体长无关的抗水流能力差异。本研究结果表明，两种鱼类在生态形态空间与游泳能力上均存在差异，支持如下假说：水流水动力越强，鱼类的抗水流能力越佳，且该能力与鱼类游泳活动相关的形态特征显著相关。