Comparative cytogenetics of Astyanax (Teleostei: Characidae) from the upper Paraguay basin

Abstract

Astyanax is one of the most abundant and diverse taxa of fishes in the Neotropical region. In order to increase the amount of cytogenetic information for Astyanax as well as to exhibit data to subsidize future taxonomic studies, this work analyzed three species of Astyanax: two species are cryptic, and are here reported to live in syntopy (A. abramis and A. lacustris); the first karyotype description for A. pirapuan is also presented. Cytogenetic analyzes reveal a diploid number of 2n=50 chromosomes for three species, yet with differences in their karyotype morphology. The physical mapping of 18S rDNA showed up to thirteen sites in A. pirapuan and two in A. abramis and A. lacustris. The physical mapping of 5S rDNA has proven to be an effective marker for the characterization of species of Astyanax studied in this work.

Characterization of a new cytotype and ocurrence of a B microchromosome in two spot astyanax, Astyanax bimaculatus Linnaeus, 1758 (Characiformes: Characidae)

“…Astyanax is the most diversified genus in the Characidae family, comprising currently 125 valid species (Fricker et al ., 2022). In addition, this group is characterized by high morphological conservatism, as well as being considered polyphyletic, with numerous cryptic organisms belonging to species complexes (Teixeira et al ., 2018; Terán et al ., 2020).…”

“…Hence, although most of the species have a diploid number of 50, their chromosome formulae are very variable. In addition, there are Astyanax species with multiple cytotypes, natural polyploidy, and occurrence of B chromosomes in many distinct species (Pazza et al ., 2018; Silva et al ., 2015; Teixeira et al ., 2018).…”

“…It is known that species of the genus Astyanax have great chromosomal variability, which in turn has several implications for conservation and diversity (Gavazzoni et al ., 2018; Teixeira et al ., 2018). However, no cytogenetic evaluation has been performed for Amazon populations of A. bimaculatus .…”

“…The 18S rDNA and the 5S rDNA probes hybridized in only one region of the A. bimaculatus karyotype, in pairs 18 and 7, respectively (Figure 1c). The occurrence of only one cluster of these genes is a standard feature in Teleostei fish, but unlike some groups in which these clusters follow a certain pattern of distribution, this does not seem to occur in Astyanax , where such genes are found in morphologically different chromosome pairs, in addition to the presence of multiple clusters of these genes in some species (Gavazzoni et al ., 2018; Teixeira et al ., 2018). Indeed, such features represent an important marker to diagnose the relationship among populations of A. bimaculatus , as well as in other Astyanax species (Gavazzoni et al ., 2018; Tenório et al ., 2013).…”

“…group is characterized by high morphological conservatism, as well as being considered polyphyletic, with numerous cryptic organisms belonging to species complexes (Teixeira et al, 2018;Terán et al, 2020).…”