Karyotype and Mapping of Repetitive DNAs in the African Butterfly Fish <b><i>Pantodon buchholzi, </i></b>the Sole Species of the Family Pantodontidae

Abstract

The monophyletic order Osteoglossiformes represents one of the most ancestral groups of teleosts and has at least 1 representative in all continents of the southern hemisphere, with the exception of Antarctica. However, despite its phylogenetic and biogeographical importance, cytogenetic data in Osteoglossiformes are scarce. Here, karyotype and chromosomal characteristics of the lower Niger River population of the African butterfly fish Pantodon buchholzi, the sole species of the family Pantodontidae (Osteoglossiformes), were examined using conventional and molecular cytogenetic approaches. All specimens examined had 2n = 46 chromosomes, with a karyotype composed of 5 pairs of metacentric, 5 pairs of submetacentric, and 13 pairs of acrocentric chromosomes in both sexes. No morphologically differentiated sex chromosomes were identified. C-bands were located in the centromeric/pericentromeric region of all chromosomes and were associated with the single AgNOR site. FISH with ribosomal DNA probes revealed that both 5S and 18S rDNA were present in only 1 pair of chromosomes each, but did not colocalize. CMA₃⁺ bands were observed near the telomeres in several chromosome pairs and also at the 18S rDNA sites. The mapping of di- and trinucleotide repeat motifs, Rex6 transposable element, and U2 snRNA showed a scattered distribution over most of the chromosomes, but for some microsatellites and the U2 snRNA also a preferential accumulation at telomeric regions. This study presents the first detailed cytogenetic analysis in the African butterfly fish by both conventional and molecular cytogenetic protocols. This is the first of a series of further cytogenetic and cytogenomic studies on osteoglossiforms, aiming to comprehensively examine the chromosomal evolution in this phylogenetically important fish order.

From Chromosomes to Genome: Insights into the Evolutionary Relationships and Biogeography of Old World Knifefishes (Notopteridae; Osteoglossiformes)

“…Therefore, we cannot exclude the incidence of chromosomal variation among P. afer populations, or even that another Papyrocranus species, P. congoensis , has been analyzed instead. In fact, a similar inconsistency was also found for another osteoglossiform species, butterfly fish, Pantodon buchholzi , in which 2n = 46 occurs in individuals from the lower Niger River basin [ 19 ], compared to uncertain chromosome numbers (2n = 46 or 48) previously reported by [ 22 ] for individuals of unknown origin. Interestingly, the karyotype of P. afer possess 2n = 50, i.e., chromosome number hypothesized as basal and/close to 2n for teleosts [ 55 ], and as compared to karyotypes of all other notopterids, also contains bi-armed elements in karyotype.…”

“…In this line, karyotype investigations were coupled with analysis of genetic distance based on high-resolution sequencing data, and biogeographic analyses may provide further powerful insight into such problems. Although it constitutes a particular model for biogeographic and evolutionary studies [ 4 , 6 , 18 ], the cytotaxonomy of representatives within the order Osteoglossiformes is still insufficiently known, with most of the available data predating the development of modern molecular cytogenetic approaches [ 19 , 20 ]. These traditional data are restricted to the determination of diploid chromosome numbers (2n) and the basic karyotype descriptions of several representatives of all main Osteoglossiformes’ lineages.…”

“…These traditional data are restricted to the determination of diploid chromosome numbers (2n) and the basic karyotype descriptions of several representatives of all main Osteoglossiformes’ lineages. Despite their intrinsic limitation, such data have already demonstrated significant karyotype diversity among lineages, with an absence of heteromorphic sex chromosomes in most species [ 19 ]. To date six notopterid species were studied using only conventional cytogenetic analyzes ( Table 1 ).…”

Dynamics of tandemly repeated DNA sequences during evolution of diploid and tetraploid botiid loaches (Teleostei: Cobitoidea: Botiidae)

“…: [ 89 , 123 – 125 ]), with our study adding the first records for Cypriniformes. About half of the surveyed teleost fish species exhibits a single pair of U2-bearing chromosomes and internal or proximal chromosomal localization [ 89 , 105 , 124 ].…”

Comparative chromosomal mapping of microsatellite repeats reveals divergent patterns of accumulation in 12 Siluridae (Teleostei: Siluriformes) species

“…These sequences were selected from a pool of microsatellite repeats since they are commonly accumulated in several fish genomes (e.g. Nanda et al, 1990;Vanzela et al, 2002;Martins, 2007;Cioffi et al, 2011;Cioffi and Bertollo, 2012;Poltronieri et al, 2014;Cioffi et al, 2015;Pucci et al, 2016;Ráb et al, 2016;Sassi et al, 2019;Supiwong et al, 2019) We performed at least three repetitions for each experiment and analyzed at least 30 metaphases per experiment to check the consistency of the results. Images were captured using an Olympus BX50 microscope (Olympus Corporation, Ishikawa, Japan) with CoolSNAP and processed using Image-Pro Plus 4.1 software (Media Cybernetics, Silver Spring, MD, USA).…”