Hidden Diversity in Eigenmannia (Gymnotiformes: Sternopygidae) Populations from Upper Paraná and Paraguay Rivers.

Eigenmannia is a highly diverse genus within the Sternopygidae family, comprising 30 species. Due to its complex taxonomy, molecular analyses have been crucial for species delimitation within this group. Therefore, the present study presents a genetic analysis using sequences of the mitochondrial gene cytochrome c oxidase subunit 1 (COI) in specimens previously identified through alpha taxonomy as E. correntes (with unpublished data), E. virescens, and E. trilineata, originating from various locations within the Upper Paraná and Paraguay River basins in Brazil. The molecular data confirm the taxonomic complexity of the genus, as individuals morphologically identified as E. virescens and E. trilineata shared the same haplotype (H52). Furthermore, the results of the species delimitation tests suggest that specimens morphologically identified as E. virescens belong to the species E. trilineata. In addition, samples morphologically identified as E. correntes may correspond to more than one Operational Taxonomic Units (OTUs). Furthermore, the intraspecific Kimura-2-parameter (K2P) distances within the different studied populations are significant. This study has contributed valuable information about genetic diversity in Eigenmannia, emphasizing the importance of using integrative analyses to resolve taxonomic conflicts within the group. It also supports biogeographical studies and assists in biodiversity conservation efforts.

Cytogenetic and Molecular Characterization of Eigenmannia aff. desantanai (Gymnotiformes: Sternopygidae): A First Report of System of Sex Chromosomes ZW1W2/ZZ in Gymnotiformes.

Gymnotiformes a monophyletic group of fish endemic to the Neotropics, represent an important component of the freshwater ichthyofauna that presents relevant taxonomic problems. Thus, in view of the morphological complexity involving Eigenmannia (Gymnotiformes) fish species, this study aimed to characterize Eigenmannia aff. desantanai of the upper Paraguay River basin through cytogenetic and molecular analyses, to help in the correct identification and delimitation of species. This study reports a multiple sex system of the type ZW1W2/ZZ, with 2n = 31 for females and 2n = 30 for males. A single pair of chromosomes carrying the nucleolar organizing regions (NORs) was detected. The heterochromatin was colocated in NOR sites and mainly located in the centromeric regions of chromosomes. Besides that, individual sequences COI from the specimens of E. aff. desantanai were obtained, totalizing three haplotypes. The distance p between the haplotypes in E. aff. desantanai, ranged from 0.2% to 7.1%. Species delimitation tests indicated the existence of two possible operational taxonomic units of E. aff. desantanai. Thus, this study reports a new multiple sex system in Gymnotiformes and these specimens previously identified as E. aff. desantanai may belong to two distinct species.