Chromosomal Evolution in Aspredinidae (Teleostei, Siluriformes): Insights on Intra- and Interspecific Relationships with Related Groups

Abstract

The family Aspredinidae comprises a clade of complex systematic relationships, both from molecular and morphological approaches. In this study, conventional and molecular cytogenetic studies coupled with nucleotide sequencing were performed in 6 Aspredininae species (<i>Amaralia hypsiura</i>, <i>Bunocephalus</i> cf. <i>aloikae</i>, <i>Bunocephalus amaurus</i>, <i>Bunocephalus</i> aff. <i>coracoideus</i>, <i>Bunocephalus verrucosus</i>, and <i>Platystacus cotylephorus</i>) from different locations of the Amazon hydrographic basin. Our results showed highly divergent diploid numbers (2n) among the species, ranging from 49 to 74, including the occurrence of an XX/X0 sex chromosome system. A neighbor-joining phylogram based on the cytochrome <i>c</i> oxidase I (<i>COI</i>) showed that <i>Bunocephalus coracoideus</i> is not a monophyletic clade, but closely related to <i>B. verrucosus.</i> The karyotypic data associated with <i>COI</i> suggest an ancestral karyotype for Aspredinidae with a reduced 2n, composed of bi-armed chromosomes and a trend toward chromosomal fissions resulting in higher diploid number karyotypes, mainly composed of acrocentric chromosomes. Evolutionary relationships were discussed under a phylogenetic context with related species from different Siluriformes families. The karyotype features and chromosomal diversity of Aspredinidae show an amazing differentiation, making this family a remarkable model for investigating the evolutionary dynamics in siluriforms as well as in fish as a whole.