Abstract
Available data on cytotaxonomy of the genus Characidium Reinhardt, 1867, which contains the greatest number of species in the Characidiinae (Crenuchidae), with 64 species widely distributed throughout the Neotropical region, were summarized and reviewed. Most Characidium species have uniform diploid chromosome number (2n) = 50 and karyotype with 32 metacentric (m) and 18 submetacentric (sm) chromosomes. The maintenance of the 2n and karyotypic formula in Characidium implies that their genomes did not experience large chromosomal rearrangements during species diversification. In contrast, the internal chromosomal organization shows a dynamic differentiation among their genomes. Available data indicated the role of repeated DNA sequences in the chromosomal constitution of the Characidium species, particularly, in sex chromosome differentiation. Karyotypes of the most Characidium species exhibit a heteromorphic ZZ/ZW sex chromosome system. The W chromosome is characterized by high rates of repetitive DNA accumulation, including satellite, microsatellite, and transposable elements (TEs), with a varied degree of diversification among species. In the current review, the main Characidium cytogenetic data are presented, highlighting the major features of its karyotype and sex chromosome evolution. Despite the conserved karyotypic macrostructure with prevalent 2n = 50 chromosomes in Characidium, herein we grouped the main cytogenetic information which led to chromosomal diversification in this Neotropical fish group.
Highlights
Crenuchidae (Teleostei: Characiformes) include 18 genera and 95 species (Eschmeyer et al 2018), grouped in Crenuchinae and Characidiinae (Buckup 1999)
The molecular characterization and chromosome mapping of the histone genes H1, H3 and H4 were described for C. zebra and C. gomesi (Pucci et al 2018). These three histone sequences appear to be associated with transposable elements (TEs) and, in situ localization, revealed that they are dispersed throughout the autosomes, but they are not involved in the differentiation of the specific region of the W sex chromosome in C. gomesi (Pucci et al 2018)
Chromosomal diversification in Characidium here revised show a diversified karyotype microstructure despite its conserved karyotypic macrostructure with prevalent 2n of 50 chromosomes arranged in 32 m + 18 sm
Summary
Crenuchidae (Teleostei: Characiformes) include 18 genera and 95 species (Eschmeyer et al 2018), grouped in Crenuchinae and Characidiinae (Buckup 1999). This data indicated that the ITS signals found in genomes of some Characidium species (Fig. 2a) do not have relation with chromosome fusions but, on contrary, are associated with repetitive DNAs dispersion (Scacchetti et al 2015c).
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