Anna Maria Deiana

Major and 5S ribosomal sequences of the largemouth bass Micropterus salmoides (Perciformes, Centrarchidae) are localized in GC-rich regions of the genome

Major and 5S ribosomal genes have been localized in the chromosomes of Micropterus salmoides. By C-banding, Ag-staining, CMA3-staining and 45S and 5S fluorescence in-situ hybridization (FISH), we demonstrate that the 45S and 5S ribosomal genes are clustered in two different chromosome pairs and both are located in heterochromatic GC-rich regions. PCR amplification and sequencing of the 5S intergenic non-transcribed sequences have allowed us to identify variability essentially due to a trinucleotide tandem repeat (GCT).

The characterization of somatic chromosomes of Gymnothorax unicolor (Delaroche, 1809) by C-banding and NOR staining (Osteichthyes, Anguilliformes)

The diploid chromosome number of Gymnothorax unicolor (Delaroche, 1809) is 2n=42, the karyotype comprising six pairs of meta-submetacentric and fifteen pairs of acrocentric chromosomes. C-positive chromatin is present in the centromeres of all chromosomes as well as in the paracentromeric regions of some chromosomes. A nucleolar organizer region was identified on the long arm of chromosome 9, near the centromere. This region is also positive to C-banding.Cytotaxonomical relationships are evidenced between the described karyotype and that of the related species Muraena helena.

Mitochondrial DNA variability in Anguilla anguilla and phylogenetical relationships with congeneric species

Abstract To obtain genetic molecular markers, valuable for the explanation of intraspecific variability, we have sequenced and compared a region of the mitochondrial cytochrome b (Cyt‐b) of seven European eels, Anguilla anguilla (L.), from four different Italian sites. The alignment of the seven sequences shows the existence of 14 variable sites, due to nucleotidic substitutions which are evolutively neutral. Alignment of the A. anguilla Cyt‐b sequences with the corresponding sequences from A. rostrata and A. japonica (both available in the EMBL DNA database) identifies some interspecific differences. A phylogenetic analysis by the neighbour‐joining method clearly confirms the genetic separation and the monophyletic origin of the three species. Six and twenty base substitutions, which are common to all the samples of A. anguilla, can be diagnostic candidates for the interspecific differences of this species with A. rostrata and A. japonica, respectively.

Benthic mucilagenous aggregates: Biochemical characterization and ligand binding properties

Abstract The biochemical composition of benthic mucilaginous aggregates collected from the south-western coastal waters of Sardinia in the Mediterranean Sea was analysed. Acidic glycoproteins surrounding the included microorganisms, mainly diatoms, were found to be the predominant fraction. The aggregates, diluted and finely dispersed by ultrasonic treatment, bound with ammoniated ruthenium oxychloride (ruthenium red), a specific ligand for the acidic glycoproteins. When concentrated crude aggregates were used, ruthenium red was bound both chemically and by physical entrapment. The data were consistent with the Langmuir ligand binding isotherm. The extent of physical adsorption displayed a clear pH dependence. Physical adsorption was predominant at acidic pH, suggesting that the stabilization of the supramolecular structure of the aggregates also depends on the degree of protonation of the acidic glycoresidues. A structural model of the aggregates is proposed, where the mucus matrix containing acidic binding sites acts as an intercellular glue, providing a molecular sieve-like filtering capacity to the aggregates dispersed in seawater.

Diet and feeding habits of two skate species, Raja brachyura and Raja miraletus (Chondrichthyes, Rajidae) in Sardinian waters (central‐western Mediterranean)

The diet and inter‐ and intraspecific interactions of two shallow‐water skates, Raja brachyura and R. miraletus, caught at depths between 30 and 162 m during trawl surveys carried out in 2005 and 2006 in the seas surrounding Sardinia (central‐western Mediterranean), were analysed. The low values of Levin and Shannon indexes (Bi = 0.37 and 0.42, respectively, for the former, and H′ = 1.31 and 1.62, respectively, for the latter) showed that these two species are specialized predators. An ontogenetic analysis of the diets of three size groups showed that they adopted similar trophic habits. Young R. brachyura specimens (Bi = 0.27; H′ = 1.05) feed mainly on Crustacea (% IRI = 74) (mainly Mysidiacea and Amphipoda Gammaridea), which were replaced in the diet of medium‐large specimens principally by Osteichthyes (mainly Gymnammodytes cicerelus). Multidimensional scaling analysis indicated a high level of intraspecific competition between medium and large individuals. In R. miraletus, Crustacea represented the main prey in all size groups (% IRI = 99.5, 99.6, and 88, respectively). Amphipoda Gammaridea were the predominant prey for small individuals, and were replaced in medium and large specimens by decapods. Low levels of interspecific competition were generally found.

Abnormal rostrum in Polycheles typhlops Heller, 1862 (Decapoda: Polychelidae) from the Central Western Mediterranean

Abstract Anomalies of the number of rostral spines have been recorded in blind lobsters, Polycheles typhlops, caught in Sardinian waters (Central Western Mediterranean). The abnormal specimens, 66 out a total of 789 individuals analysed, showed all the morphometric characteristics of P. typhlops except for the unusual presence of two rostral spines instead of the canonical one. The analysis of partial nucleotide sequences of the mitochondrial cytochrome oxidase subunit I gene (COI) showed that the individuals with two spines were not genetically different from the normal specimens of P. typhlops, while both were quite dissimilar from the other Mediterranean species, P. sculptus. Our results suggest the need of an update of the morphological classification guides for this family combined with a wider genetic study.

Colocalization of the ribosomal gene families in Conger conger (Anguilliformes, Congridae)

The location of the major and minor ribosomal gene families in the conger eel (Conger conger) was investigated by in situ hybridization and CMA3 staining. The two gene families were localized in only one chromosome pair, on the short arm of pair 19, in an entirely CMA3‐positive region. Among the Anguilliformes, C. conger is the only species that shows the presence of the two gene families in the same chromosomal region.

B chromosomes in Crustacea Decapoda

Among crustacean Decapoda numerical chromosome variability is frequent, and it has been hypothesized that the presence of supernumerary chromosomes accounts for this variability. Thanks to the improvement of cytogenetic analysis by chromosomal banding techniques, supernumerary B chromosomes (Bs) have been demonstrated in Nephrops norvegicus, Homarus americanus,Palinurus elephas and P. mauritanicus, belonging to different crustacean families. In all four species Bs were variable in number, mainly heterochromatic and undigested by various endonucleases, and in meiosis they showed non-Mendelian segregation. Compared to the other chromosomes of the complement, the Bs are very small in almost all species, but some of them were very large in N. norvegicus.

Developmental changes in the content of dopamine in the olfactory bulb of the European eel (Anguilla anguilla)

The concentrations of dopamine (DA) and of its major metabolite, dihydroxyphenylacetic acid (DOPAC), were measured in discrete areas of the eel brain. To investigate the developmental changes in the content of DA and DOPAC, the assays were performed in yellow eels (i.e. at the feeding stage) and silver eels (i.e. at the migratory stage). DA and DOPAC were unevenly distributed in the eel brain. In yellow eels, the concentration of DA was highest (16-19 pmol/mg protein) in the olfactory bulb (OB), mesencephalic tectum-diencephalon (MT-D) and medulla oblongata (MO) and lowest in the cerebellum (CB, 1 pmol/mg protein), whereas intermediate values were measured in the telencephalon (TE; 10 pmol/mg protein). The metabolic rate of DA, as reflected by the DOPAC/DA ratio, was highest in the OB and CB, with progressively smaller values being observed in the TE, MT-D, and MO. A significant increase in the concentrations of DA (+80%) and DOPAC (+122%) was observed in the OB of silver eels compared with yellow eels, whereas no significant differences were detected in the concentrations of DA and DOPAC in the other brain areas as a function of the developmental stage. The results are discussed in terms of the possible involvement of environmental, behavioral and developmental factors.

Karyotype, C- and G-banding, and nucleolar organizer regions of Conger conger (Osteichthyes, Anguilliformes)

Abstract The diploid chromosome number of Conger conger L. was found to be 2n = 38, with the karyotype consisting of four pairs of metacentric, two of submetacentric and thirteen of acrocentric chromosomes. C‐ and G‐banding allowed the identification of homologous chromosomes. NOR was identified on the short arm of the smallest acrocentric pair.