Evolutionary tracks of chromosomal diversification in Trichopsis (Anabantiformes, Osphronemidae) fishes: New insights from a molecular cytogenetic perspective

Abstract

This study investigated the chromosomes of three Trichopsis species (namely Trichopsis pumila, Trichopsis vittata, and Trichopsis schalleri) using conventional (Giemsa stain, Ag-NOR) and molecular cytogenetic techniques. Fluorescence in situ hybridization (FISH) with repetitive DNAs, including 5S and 18S rDNAs, and microsatellites as probes were also performed. Our results indicated a conserved diploid number of 46 (2n) for all analyzed species of both sexes, although varying in their karyotype structure. Furthermore, T. schalleri and T. vittata karyotypes were presented with only acrocentric chromosomes (46a), while T. pumila had a submetacentric pair in addition to acrocentric ones (2sm+44a). Positive Ag-NOR sites were differentially found in each species adjacent to the acrocentric chromosome's centromeric and/or interstitial sub-centromeric regions. Both 5S and 18S rDNAs vary between the analyzed species, but all were localized in multiple sites. However, the distribution pattern of microsatellites differed in each species, mostly scattering at peri-centromeric and telomeric regions. These findings show that Trichopsis species, while having a conserved diploid number, differ significantly in the distribution of repetitive sequences in their karyotypes, particularly for rDNAs. These species-specific patterns can be useful for characterizing and identifying further different species and examining the evolutionary mechanisms that drove the evolution of these fishes' karyotypes.