Polymorphism of the rDNA Chromosomal Regions in the Weatherfish Misgurnus fossilis (Teleostei: Cobitidae)

Hopfinger

et al. 2021

The European weatherfish Misgurnus fossilis (Linnaeus, 1758) is a threatened freshwater species in large parts of Europe and might come under pressure from currently establishing exotic weatherfish species. Additional threats might arise if those species hybridize which has been questioned in previous research. Regarding the hybridization of M. fossilis × M. anguillicaudatus (Cantor, 1842), we demonstrate that despite the considerable genetic distance between parental species, the estimated long divergence time and different ploidy levels do not represent a postzygotic barrier for hybridization of the European and Oriental weatherfish. The paternal species can be easily differentiated based on external pigment patterns with hybrids showing intermediate patterns. No difference in standard metabolic rate, indicating a lack of hybrid vigour, renders predictions of potential threats to the European weatherfish from hybridization with the Oriental weatherfish difficult. Therefore, the genetic and physiological basis of invasiveness via hybridization remains elusive in Misgurnus species and requires further research. The existence of prezygotic reproductive isolation mechanisms and the fertility of F1 hybrids remains to be tested to predict the potential threats of globally invasive Oriental weatherfish species.

“…8). The definitive lack of lower metabolic rates in the European weatherfish might be interpreted as a hint towards the secondary rediploidization in M. fossilis (Spóz et al 2017).…”

Section: Discussionmentioning

confidence: 96%

First successful hybridization experiment between native European weatherfish (Misgurnus fossilis) and non-native Oriental weatherfish (M. anguillicaudatus) reveals no evidence for postzygotic barriers

Hopfinger

et al. 2021

“…Major rDNA is usually visualized by 18S or 28S rDNA probes. Despite the ever-growing number of studies showing lability of their site number and patterns of distribution in fish genomes (with many cases documenting intra-and inter-populational variability) (see, e.g., in [66][67][68]) and even their vulnerability to change rapidly under different environmental conditions [69] or hybridization [70], certain arrangements of rDNA classes can help to clarify a presence of species complexes or cryptic species (see, e.g., in [71][72][73]), to uncover the genome composition in hybrid specimens [74,75], to confirm the ploidy level, and to deduce the mechanism of polyploidy [76][77][78][79]. It has been repeatedly documented that even closely related species may possess dramatically different number of rDNA loci [45,71,80].…”

Section: Discussionmentioning

confidence: 99%

Taxonomic Diversity Not Associated with Gross Karyotype Differentiation: The Case of Bighead Carps, Genus Hypophthalmichthys (Teleostei, Cypriniformes, Xenocyprididae)

Sember

Pelikánová

Cioffi

et al. 2020

Genes

The bighead carps of the genus Hypophthalmichthys (H. molitrix and H. nobilis) are important aquaculture species. They were subjected to extensive multidisciplinary research, but with cytogenetics confined to conventional protocols only. Here, we employed Giemsa-/C-/CMA3- stainings and chromosomal mapping of multigene families and telomeric repeats. Both species shared (i) a diploid chromosome number 2n = 48 and the karyotype structure, (ii) low amount of constitutive heterochromatin, (iii) the absence of interstitial telomeric sites (ITSs), (iv) a single pair of 5S rDNA loci adjacent to one major rDNA cluster, and (v) a single pair of co-localized U1/U2 snDNA tandem repeats. Both species, on the other hand, differed in (i) the presence/absence of remarkable interstitial block of constitutive heterochromatin on the largest acrocentric pair 11 and (ii) the number of major (CMA3-positive) rDNA sites. Additionally, we applied here, for the first time, the conventional cytogenetics in H. harmandi, a species considered extinct in the wild and/or extensively cross-hybridized with H. molitrix. Its 2n and karyotype description match those found in the previous two species, while silver staining showed differences in distribution of major rDNA. The bighead carps thus represent another case of taxonomic diversity not associated with gross karyotype differentiation, where 2n and karyotype structure cannot help in distinguishing between genomes of closely related species. On the other hand, we demonstrated that two cytogenetic characters (distribution of constitutive heterochromatin and major rDNA) may be useful for diagnosis of pure species. The universality of these markers must be further verified by analyzing other pure populations of bighead carps.

“…In most fishes [ 104 – 106 ], including other loach families [ 51 – 53 , 55 ] the ancestral diploid pattern appears to be one pair of NOR/45S rDNA sites and the emerging information suggest similar scenario for U2 snDNA. In 5S rDNA, however, the situation has been found to be too variable and complex to reconstruct the ancestral situation ([ 106 , 107 ]; for examples in loaches and cypriniform polyploids, see: [ 30 , 33 , 50 , 53 , 55 , 108 ]). Contrary to expectations, our present results show that the number of 45S rDNA signals range from two to six in diploid botiids, thereby exceeding frequently the expected number.…”

Section: Discussionmentioning

confidence: 99%

“…To date, cytogenetic reports in Botiidae are limited to conventional Giemsa-stained karyotypes or basic chromosome counts [ 42 , 44 , 47 – 49 ], while molecular cytogenetic data like those scarcely published in sister loach groups (namely Cobitidae and Nemacheilidae; [ 50 – 55 ]) are yet non-existent for this lineage.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2018

Polyploidization has played an important role in the evolution of vertebrates, particularly at the base of Teleostei–an enormously successful ray-finned fish group with additional genome doublings on lower taxonomic levels. The investigation of post-polyploid genome dynamics might provide important clues about the evolution and ecology of respective species and can help to decipher the role of polyploidy per se on speciation. Few studies have attempted to investigate the dynamics of repetitive DNA sequences in the post-polyploid genome using molecular cytogenetic tools in fishes, though recent efforts demonstrated their usefulness. The demonstrably monophyletic freshwater loach family Botiidae, branching to evolutionary diploid and tetraploid lineages separated >25 Mya, offers a suited model group for comparing the long-term repetitive DNA evolution. For this, we integrated phylogenetic analyses with cytogenetical survey involving Giemsa- and Chromomycin A3 (CMA3)/DAPI stainings and fluorescence in situ hybridization with 5S/45S rDNA, U2 snDNA and telomeric probes in representative sample of 12 botiid species.The karyotypes of all diploids were composed of 2n = 50 chromosomes, while majority of tetraploids had 2n = 4x = 100, with only subtle interspecific karyotype differences. The exceptional karyotype of Botia dario (2n = 4x = 96) suggested centric fusions behind the 2n reduction. Variable patterns of FISH signals revealed cases of intraspecific polymorphisms, rDNA amplification, variable degree of correspondence with CMA3+ sites and almost no phylogenetic signal. In tetraploids, either additivity or loci gain/loss was recorded. Despite absence of classical interstitial telomeric sites, large blocks of interspersed rDNA/telomeric regions were found in diploids only.We uncovered different molecular drives of studied repetitive DNA classes within botiid genomes as well as the advanced stage of the re-diploidization process in tetraploids. Our results may contribute to link genomic approach with molecular cytogenetic analyses in addressing the origin and mechanism of this polyploidization event.