Evolutionary Relationships among <b><i>Boulengerella</i></b> Species (Ctenoluciidae, Characiformes): Genomic Organization of Repetitive DNAs and Highly Conserved Karyotypes

Abstract

Ctenoluciidae is a Neotropical freshwater fish family whose representatives are known as bicudas. The genus Boulengerella contains 5 species, and 4 of them (B. cuvieri, B. lateristriga, B. lucius, and B. maculata) were cytogenetically analyzed in the present study by conventional and molecular procedures. All 4 species have a very similar karyotype, with 2n = 36 chromosomes (14 metacentrics + 16 submetacentrics + 6 subtelocentrics; FN = 72). However, the heterochromatin distribution pattern is species-specific. In all 4 species, the nucleolus organizer region is located in pair 18, as also confirmed by cytogenetic mapping of 18S rDNA. In turn, 5S rRNA genes are present in 2 chromosome pairs: in pair 1 of all 4 species, and in pair 10 of B. lateristriga, B. maculata, and B. cuvieri, but in pair 4 of B. lucius. The telomeric probe highlighted terminal regions in all chromosomes, as well as an interstitial centromeric sequence in pair 3 of the 3 first-mentioned species. Notably, a conspicuous heteromorphic secondary constriction in chromosomes 18 was found only in the males of the 3 species, rendering one of the homologs much larger than the other one. This feature, associated with a large 18S rDNA block and accumulation of telomeric sequences, suggests the presence of an XX/XY sex chromosome system in the analyzed Boulengerella species.

First Chromosomal Analysis in Hepsetidae (Actinopterygii, Characiformes): Insights into Relationship between African and Neotropical Fish Groups

“… Representative idiograms of Hepsetus odoe and Pyrrhulina (Lebiasinidae) (data from Moraes et al, 2017 ) and Boulengerella (Ctenoluciidae) (data from de Souza E Sousa et al, 2017 ) species. The distribution of the 18S and the 5S rDNAs for each species are highlighted in red and green, respectively.…”

“…As regards to Ctenoluciidae, four species of the Boulengerella genus from the Amazon River basin (Brazil), showed 2n = 36 and a very similar karyotype organization. A conspicuous chromosomal heteromorphism in male specimens point to a possible XX/XY sex chromosome system in such species ( de Souza E Sousa et al, 2017 ). Besides, Ctenolucius hujeta (2n = 36) is the only additional species of Ctenoluciidae that has its chromosomal number already analyzed ( Arefjev, 1990 ), coinciding with those found for the Boulengerella species.…”

Centric Fusions behind the Karyotype Evolution of Neotropical Nannostomus Pencilfishes (Characiforme, Lebiasinidae): First Insights from a Molecular Cytogenetic Perspective

“…With a few exceptions, the terminal position of the 18S rDNA loci on chromosomes appears to be a common feature for all Lebiasinidae genera analyzed up to now (i.e., Nannostomus, Pyrrhulina, Lebiasina, and Copeina) ( [19][20][21][22], this study). Altogether with Ctenoluciidae [37], this pattern can be considered as symplesiomorphy for both families. Although 5S rDNA displays a more dynamic evolution, with both terminal and interstitial signals among lebiasinids ( [19][20][21][22], this study), it is noteworthy that N. unifasciatus underwent structural chromosome rearrangements involving both 18S and 5S rDNA loci, which have led to a derived pattern of rDNA distribution in this species.…”

“…For this, the modal 2n of characiform fishes and the phylogenetic relationship of Nannostomus with the nearest lebiasinid lineages may provide a first useful indication (the principle reviewed in Dobigny et al [35]). Thus, taking into account that (1) the modal 2n for characiforms very likely may be 2n = 54 [36], (2) Lebiasina, the most basal genus of Lebiasinidae [14] is characterized by 2n = 36 [21], and (3) the same 2n is also present among Ctenoluciidae species [37], a probable sister family of Lebiasinidae [38], we can infer that the reduction of 2n among the Nannostomus species was most likely achieved by a series of chromosome fusions. Specifically, according to Benzaquem et al [15], N. unifasciatus, with 2n = 22 and with a karyotype formed exclusively by bi-armed chromosomes, is phylogenetically closely related to N. beckfordi, which possesses 2n = 44 and a karyotype formed by acrocentric chromosomes only.…”

Interspecific cytogenetic relationships in three Acestrohynchus species (Acestrohynchinae, Characiformes) reveal the existence of possible cryptic species

“…In this case, there was a larger ITS in one of the homologs, indicating the translocation of a telomeric sequence to this chromosome (Ruiz-Herrera et al 2008;Bolzán 2017) and its duplication. An ITS may indicate the presence of chromosomal rearrangements during the evolutionary process, leading to the differentiation of the karyotypes of different species, as observed in several fish families (Meyne et al 1989;Mota-Velasco et al 2010;Cioffi and Bertollo 2012;Ocalewicz 2013;Sousa e Souza et al 2017).…”