Chromosomal analysis of Centromochlus heckelii (Siluriformes: Auchenipteridae), with a contribution to Centromochlus definition

ABSTRACT Historically, there are divergences in the species allocation between Centromochlus and Tatia. This study aimed to generate the first cytogenetic data about Centromochlus and, by analyzing a population of Centromochlus heckelii from the Amazon River basin, to contribute as evidence to a historical taxonomic dilemma. Diploid number of 46 chromosomes and a heteromorphic pair was found in the female karyotypes, thus characterizing a ZZ/ZW sex chromosome system. Pale blocks of heterochromatin were located in centromeric regions of some chromosomes; however, the exclusive female chromosome (W) is almost entirely heterochromatic. AgNORs were detected in terminal position on the short arms of one acrocentric pair in males and two chromosome pairs in females, the acrocentric plus the sex chromosome pair. Notable differences between Centromochlus heckelii and previous data about species of Tatia are: lower diploid number, presence of a sex chromosome system and multiple AgNORs in Centromochlus, while species of Tatia have simple AgNORs and the absence of acrocentric chromosomes. Results in this study show that chromosomal markers could contribute as evidence to taxonomic delimitation studies.

摘要 历史上，平鳍鮠属（Centromochlus）与塔氏鮠属（Tatia）在物种分类上始终存在分歧。本研究首次获取了平鳍鮠属的细胞遗传学数据，通过分析采自亚马逊河流域的赫氏平鳍鮠（Centromochlus heckelii）种群，为这一长期存在的分类学困境提供佐证依据。研究发现，雌性核型的二倍体染色体数为46条，且存在一对异形染色体，由此确定其性别染色体系统为ZZ/ZW型。部分染色体的着丝粒区域分布有浅染异染色质块，而特有雌性W染色体几乎完全由异染色质构成。银染核仁组织者区（AgNORs）定位于雄性一对近端着丝粒染色体短臂的末端位置；雌性则存在两处银染核仁组织者区，分别对应一对近端着丝粒染色体与性染色体对。赫氏平鳍鮠与既往塔氏鮠属物种的研究数据存在显著差异：平鳍鮠属物种的二倍体染色体数更低、存在性别染色体系统且具有多个核仁组织者区，而塔氏鮠属物种仅具备单个核仁组织者区，且不存在近端着丝粒染色体。本研究结果表明，染色体标记可为物种分类界定研究提供有效佐证。