Cytogenetic markers as tools in delimiting species of the highly diverse Neotropical fish Bryconamericus (Characiformes: Characidae)

Abstract

Bryconamericus is a highly diverse group of characid fishes, being cytogenetic a valuable tool for the delimitation of species. Bryconamericus aff. iheringii (Upper Uruguay/Lower Paraná), B. coeruleus (Upper Paraná), B. cf. ecai e B. cf. eigenmanni (Upper Uruguay) were studied cytogenetically, and presented 2n=52 chromosomes, with interpopulational/interspecific variation of karyotype and fundamental number. Heterochromatin was evidenced in pericentromeric, telomeric and interstitial regions, and it was shown to be an important cytogenetic marker. Single nucleolar organizing regions (NORs) were found in B. cf. eigenmanni, B. cf. ecai and B. aff. iheringii (Lower Paraná), and multiple in B. aff. iheringii (Upper Uruguay) and B. coeruleus, with occurrence of two patterns for the first species, and three for the second. The 5S/18S rDNA-FISH confirmed the location of the NORs and showed single 5S rDNA cistrons only in B. aff. iheringii (Lower Paraná), evidencing the dispersion of both genes, often co-located, in the karyotype of the others species. The data of this work contribute for the delimitation of the species of the genus. Co-localization of ribosomal genes may represent a plesiomorphic condition for the group, and their dispersion suggest the occurrence of duplication, pseudogeneization and transposition events mediated by mobile genetic elements.

Revision of Bryconamericus (Characiformes, Characidae) from Pacific coastal and Amazon River drainages with descriptions of three new species

“…With respect to their proposed revalidation of the genus Eretmobrycon, it is worth noting that in light of their findings, the limits of the genera Bryconamericus, Knodus, Eretmobrycon, Hemibrycon, etc. and the number of species assigned to each is called in to question, and must now be reinterpreted, based on additional molecular characters in combination with morphology, cytogenetic markers biogeographical and even ecological characters, some species were transferred to different genera without explanation (Bortoncello Prestes et al 2019;Mirande 2018;Román-Valencia et al 2017;2018;Román-Valencia, 2021); Teran et al (2020) gave a diagnosis for Eretmobrycon, and established the phylogenetic relationships of ten species using 25 molecular and seven morphological synapomorphies. Many of species and specimens examined in our studies (e.g.…”