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体现出极强的形态可塑性。明晰游泳能力、形态特征与栖息地利用之间的关联，对于预测某一物种在人为改造环境中的存续概率具有重要意义。本研究针对两种已知在不同水力生境中存在空间分隔的同域溪脂鲤属（Characidium）物种，对比了其游泳能力与形态学特征。本研究共捕获带纹溪脂鲤（Characidium fasciatum Reinhardt, 1867）个体21尾、疑似斑马溪脂鲤（Characidium cf. zebra Eigenmann, 1909）个体23尾，用于评估其游泳能力与生态形态学特征。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。本研究还对比了共计12项与栖息地利用及游泳特性相关的生态形态学特征。曼-惠特尼均值检验结果显示，带纹溪脂鲤的游泳能力强于疑似斑马溪脂鲤，且个体的标准体长可解释其抗水流能力12.42%的变异量。两种物种在尾柄相对长度、腹扁指数及胸鳍相对面积三项特征上存在显著形态差异。仅胸鳍相对面积一项，即可解释抗水流能力差异中16.71%的、无法由体长解释的部分。本研究结果表明，两种物种在生态形态空间与游泳能力上均存在差异，这支持如下假说：水体水动力越强，鱼类的抗水流能力便越强，且该能力与鱼类游泳活动相关的形态特征存在关联。