Recent chromosome diversification in the evolutionary radiation of the freshwater fish family Curimatidae (Characiformes)

Abstract

Neotropical Curimatidae fishes include 97 species in eight genera. Basic cytogenetic studies show a karyotype of 2n ¼ 54 chromosomes in most species. Karyotype divergence of the nucleolus organizing regions between species has been reported, and these regions appear to be good cytotaxonomic markers. In the present work, karyotype, heterochromatin and Ag-NOR variability in 13 species were investigated to analyse the chromosome diversification in view of the biogeographic history of this group. Only Cyphocharax platanus showed a karyotype with 2n ¼ 58 chromosomes. Ag-NOR and C-banding patterns were quite divergent among the species studied. All species whose C-bands were analysed had heterochromatic blocks associated with the nucleolus organizing regions. Species with multiple Ag-NORs also showed an increase in NOR-associated heterochromatic blocks. C-banding showed considerable differentiation among species, revealing a pronounced chromosome diversification in this group. Karyotypic variability corroborates the hypothesis that these fishes in Amazon region show various discrete patterns of species endemism. Chromosome diversification in curimatids has a recent origin and appears to be accompanying the post-Andean speciation responsible for the diversity of species in the family.

Molecular Analysis of the B Microchromosome in <b><i>Steindachnerina insculpta</i></b> (Characiformes: Curimatidae) by Microdissection

“…This karyotype structure is considered to be conserved for this group [Galetti Jr. et al, 1994;Brassesco et al, 2004;Venere et al, 2008;Sampaio et al, 2011]. According to Sampaio [2013], the karyotype evolution of curimatids is followed by slight changes in the karyotype microstructure, such as the pattern of the nucleolus organizer regions and the distribution of heterochromatin.…”

“…According to Sampaio [2013], the karyotype evolution of curimatids is followed by slight changes in the karyotype microstructure, such as the pattern of the nucleolus organizer regions and the distribution of heterochromatin. Furthermore, the presence of a B microchromosome may be a feature that distinguishes some species, demonstrating that this group may vary in some respects [Venere et al, 2008]. There are several hypotheses about the origin of B chromosomes [Camacho et al, 2000].…”

“…2007; Carvalho et al, 2008;Venere et al, 2008;Sampaio et al, 2011]. Most of the species showed inter-and intraindividual variation between 0-1 B chromosome per cell.…”

Evolutionary trends in the family Curimatidae (Characiformes): inferences from chromosome banding

“…Another feature considered a chromosomal diversification within Curimatidae is the presence of B chromosomes in some species (Vênere et al 2008). This chromosome, also called supernumerary or accessory, may exhibit either a similar morphology to that of the chromosomes of the A complement, or one that is to a clearly distinct.…”

“…This variation may be ascribable to an anaphasic delay, with the removal of B from some cells or tissues, or to meiotic nondisjunction, when both chromatids migrate to the same pole (Camacho et al 2000). Hitherto, B chromosomes have been described in seven species of Curimatidae of different populations: Cyphocharax gouldingi Vari, 1992, Cyphocharax modestus (Fernández-Yépez, 1948), Cyphocharax saladensis (Meinken, 1933), Cyphocharax spilotus (Vari, 1987), Cyphocharax voga (Hensel, 1870), Steindachnerina biornata (Braga & Azpelicueta, 1987) and Steindachnerina insculpta (Fernández-Yépez, 1948) (Sampaio et al 2011; Vênere et al 2008). …”