Evolutionary Dynamics of rDNA Clusters in Chromosomes of Five Clam Species Belonging to the Family Veneridae (Mollusca, Bivalvia)

Abstract

The chromosomal changes accompanying bivalve evolution are an area about which few reports have been published. To improve our understanding on chromosome evolution in Veneridae, ribosomal RNA gene clusters were mapped by fluorescent in situ hybridization (FISH) to chromosomes of five species of venerid clams (Venerupis corrugata, Ruditapes philippinarum, Ruditapes decussatus, Dosinia exoleta, and Venus verrucosa). The results were anchored to the most comprehensive molecular phylogenetic tree currently available for Veneridae. While a single major rDNA cluster was found in each of the five species, the number of 5S rDNA clusters showed high interspecies variation. Major rDNA was either subterminal to the short arms or intercalary to the long arms of metacentric or submetacentric chromosomes, whereas minor rDNA signals showed higher variability. Major and minor rDNAs map to different chromosome pairs in all species, but in R. decussatus one of the minor rDNA gene clusters and the major rDNA cluster were located in the same position on a single chromosome pair. This interspersion of both sequences was confirmed by fiber FISH. Telomeric signals appeared at both ends of every chromosome in all species. FISH mapping data are discussed in relation to the molecular phylogenetic trees currently available for Veneridae.

Resolving the Taxonomic Status ofChamelea gallinaandC. striatula(Veneridae, Bivalvia): A Combined Molecular Cytogenetic and Phylogenetic Approach

“…The diploid chromosome number of 2 n = 38 obtained in this work is in accordance with those previously described for C. gallina [7, 16] and all other Veneridae studied to date [6–8, 12–14]. The karyotype compositions obtained were also fundamentally coincidental with that proposed for C. gallina [16].…”

“…These differences are also present in closely related, congeneric species and are usually accompanied with an almost complete absence of intraspecific variability [7, 12–14]. …”

Molecular Cytogenetics in Trough Shells (Mactridae, Bivalvia): Divergent GC-Rich Heterochromatin Content

“…Total genomic DNA was extracted from ethanol-preserved adductor muscles following a classical method [24] with slight modifications [25]. Small pieces of tissue were homogenized in hexadecyltrimethylammonium bromide (CTAB) buffer and digested with pronase (1.5 mg/mL, 60 °C, overnight) (Sigma Aldrich, St. Louis, MO, USA) and RNase A from bovine pancreas (1 mg/mL, 37 °C, 1 h) (Sigma Aldrich, St. Louis, MO, USA).…”

Development of a comet-FISH assay for the detection of DNA damage in hemocytes of Crassostrea gigas

“…The proximity of single strand DNA loops in comet heads can promote re-annealing during the neutralization process, explaining why the number of observed signals was generally 2 in the comet head and never 8. Given the tandem repeat organization of major ribosomal genes (Long and Dawid, 1980), FISH signals could be expected to be arranged in linear arrays on comets, as observed on fibre-FISH (Pérez-García et al, 2014). However, they appeared as individual and clouds of dots, supporting the idea that the single strand DNA constituting the alkaline comet tails had coalesced into a granular form (Shaponiskov et al, 2008).…”