Integrating Genomic and Chromosomal Data: A Cytogenetic Study of Transancistrus santarosensis (Loricariidae: Hypostominae) with Characterization of a ZZ/ZW Sex Chromosome System.

The plecos (Loricariidae) fish represent a great model for cytogenetic investigations due to their variety of karyotypes, including diploid and polyploid genomes, and different types of sex chromosomes. In this study we investigate Transancistrus santarosensis a rare loricariid endemic to Ecuador, integrating cytogenetic methods with specimens' molecular identification by mtDNA, to describe the the species karyotype. We aim to verify whether sex chromosomes are cytologically identifiable and if they are associated with the accumulation of repetitive sequences present in other species of the family. The analysis of the karyotype (2n = 54 chromosomes) excludes recent centric fusion and pericentromeric inversion and suggests the presence of a ZZ/ZW sex chromosome system at an early stage of differentiation: the W chromosome is degenerated but is not characterized by the presence of differential sex-specific repetitive DNAs. Data indicate that although T. santarosensis has retained the ancestral diploid number of Loricariidae, it accumulated heterochromatin and shows non-syntenic ribosomal genes localization, chromosomal traits considered apomorphic in the family.

Taxonomic revision of the Ophidion holbrookii Putnam, 1874 (Ophidiiformes: Ophidiidae) species complex, with description of a new species from Brazil.

This study integrates morphological and molecular data to redefine the taxonomic limits of Ophidion holbrookii, as well as its geographic ranges, with the description of a new species from the eastern and southeastern coast of Brazil, South America. Ophidion zavalai n. sp. is described based on variations related to ontogeny and sexual development of swim bladder and sonic apparatus, which are likely important traits for species recognition. The description of O. zavalai n. sp. and the redefinition of distribution limits of O. holbrookii corroborate the existence of different complex species in the western Atlantic, revealing important gaps of knowledge regarding morphological variation and species habits. Ophidion zavalai n. sp. is the first species of Ophidion described from the southwestern Atlantic Ocean and contributes to evidence of a distinct coastal fauna in Brazil and surrounding areas of Argentina province.