Resolving the Taxonomic Status of<i>Chamelea gallina</i>and<i>C. striatula</i>(Veneridae, Bivalvia): A Combined Molecular Cytogenetic and Phylogenetic Approach

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Wedge shells belonging to the Donacidae family are the dominant bivalves in exposed beaches in almost all areas of the world. Typically, two or more sympatric species of wedge shells differentially occupy intertidal, sublittoral, and offshore coastal waters in any given locality. A molecular cytogenetic analysis of two sympatric and closely related wedge shell species, Donax trunculus and Donax vittatus, was performed. Results showed that the karyotypes of these two species were both strikingly different and closely alike; whilst metacentric and submetacentric chromosome pairs were the main components of the karyotype of D. trunculus, 10–11 of the 19 chromosome pairs were telocentric in D. vittatus, most likely as a result of different pericentric inversions. GC-rich heterochromatic bands were present in both species. Furthermore, they showed coincidental 45S ribosomal RNA (rRNA), 5S rRNA and H3 histone gene clusters at conserved chromosomal locations, although D. trunculus had an additional 45S rDNA cluster. Intraspecific pericentric inversions were also detected in both D. trunculus and D. vittatus. The close genetic similarity of these two species together with the high degree of conservation of the 45S rRNA, 5S rRNA and H3 histone gene clusters, and GC-rich heterochromatic bands indicate that pericentric inversions contribute to the karyotype divergence in wedge shells.

Section: Discussionmentioning

confidence: 57%

Are Pericentric Inversions Reorganizing Wedge Shell Genomes?

García-Souto¹,

Pérez-García²,

Pasantes³

2017

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“…The occurrence of major rDNA signals in a DAPI negative, GC-rich region in one chromosome pair in A. islandica is coincident with the situation in most Heterodonta, in which 24 of the 32 species analysed showed a single location for these clusters [ 16 , 17 , 19 , 20 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ]. As in ocean quahogs, nine of these 32 species displayed subcentromeric major rDNA clusters.…”

Section: Discussionmentioning

confidence: 63%

“…To date, chromosome numbers and karyotypes have been described for around 70 species of Heterodonta [ 23 , 24 , 32 , 33 , 34 , 36 , 46 , 47 , 48 , 49 , 50 ]. Although with exceptions as those in Cyrenidae, in which different levels of ploidy have been characterized [ 51 ] and Sphaeridae, whose chromosome numbers vary from 28 to 247 [ 52 ], most of these species presented diploid chromosome numbers of 2n = 38 and karyotypes showing chromosome pairs with small length differences.…”

Section: Discussionmentioning

confidence: 99%

“…Molecular cytogenetic analyses have been published for a total of 32 species of eight families of heterodont bivalves, Cardiidae [ 16 ], Donacidae [ 17 , 18 , 19 , 20 ], Mactridae [ 21 , 22 , 23 , 24 ], Pharidae [ 25 , 26 ], Psammobidae [ 27 ], Veneridae [ 21 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ], Solenidae [ 35 ] and Tellinidae [ 27 , 36 ]. Whilst in all of them diploid chromosome numbers were 2n = 38 and vertebrate type hexamere repeats (TTAGGG)n appeared just at telomeric locations, 45S rDNA, 5S rDNAs and H3 histone gene clusters showed differences in their distribution.…”

Section: Introductionmentioning

confidence: 99%

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Cytogenetics in Arctica islandica (Bivalvia, Arctidae): the Longest Lived Non-Colonial Metazoan

García-Souto

Pasantes

2018

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Due to its extraordinary longevity and wide distribution, the ocean quahog Arctica islandica has become an important species model in both aging and environmental change research. Notwithstanding that, most genetic studies on ocean quahogs have been focused on fishery related, phylogeographic and phylogenetic aspects but nothing is known about their chromosomes. In this work, the chromosomes of the ocean quahog Arctica islandica were analysed by means of 4′,6-diamidino-2-phenylindole (DAPI)/propidium iodide (PI) staining and fluorescent in situ hybridization (FISH) with rDNA, histone gene and telomeric probes. Whilst both 5S rDNA and 45S rDNA were clustered at single subcentromeric locations on the long arms of chromosome pairs 2 and 12, respectively, histone gene clusters located on the short arms of chromosome pairs 7, 10 and 17. As happens with most bivalves, the location of the vertebrate type telomeric sequence clusters was restricted to chromosome ends. The knowledge of the karyotype can facilitate the anchoring of genomic sequences to specific chromosome pairs in this species.

“…The distribution of repetitive DNAs may provide important clues about the pace of genome dynamics and it may also answer several taxonomic issues [9,10,80,81]. Chromosomal mapping of rDNA clusters has repeatedly helped to unveil diverse evolutionary issues (e.g., [82,83]).…”

Section: Discussionmentioning

confidence: 99%

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

Sember

Oliveira

Ráb

et al. 2020

Lebiasinidae is a Neotropical freshwater family widely distributed throughout South and Central America. Due to their often very small body size, Lebiasinidae species are cytogenetically challenging and hence largely underexplored. However, the available but limited karyotype data already suggested a high interspecific variability in the diploid chromosome number (2n), which is pronounced in the speciose genus Nannostomus, a popular taxon in ornamental fish trade due to its remarkable body coloration. Aiming to more deeply examine the karyotype diversification in Nannostomus, we combined conventional cytogenetics (Giemsa-staining and C-banding) with the chromosomal mapping of tandemly repeated 5S and 18S rDNA clusters and with interspecific comparative genomic hybridization (CGH) to investigate genomes of four representative Nannostomus species: N. beckfordi, N. eques, N. marginatus, and N. unifasciatus. Our data showed a remarkable variability in 2n, ranging from 2n = 22 in N. unifasciatus (karyotype composed exclusively of metacentrics/submetacentrics) to 2n = 44 in N. beckfordi (karyotype composed entirely of acrocentrics). On the other hand, patterns of 18S and 5S rDNA distribution in the analyzed karyotypes remained rather conservative, with only two 18S and two to four 5S rDNA sites. In view of the mostly unchanged number of chromosome arms (FN = 44) in all but one species (N. eques; FN = 36), and with respect to the current phylogenetic hypothesis, we propose Robertsonian translocations to be a significant contributor to the karyotype differentiation in (at least herein studied) Nannostomus species. Interspecific comparative genome hybridization (CGH) using whole genomic DNAs mapped against the chromosome background of N. beckfordi found a moderate divergence in the repetitive DNA content among the species’ genomes. Collectively, our data suggest that the karyotype differentiation in Nannostomus has been largely driven by major structural rearrangements, accompanied by only low to moderate dynamics of repetitive DNA at the sub-chromosomal level. Possible mechanisms and factors behind the elevated tolerance to such a rate of karyotype change in Nannostomus are discussed.