Museum samples could help to reconstruct the original distribution of Salmo trutta complex in Italy.

Partial D-loop sequences of museum specimens of brown trout and marble trout (Salmo trutta species complex) collected from Mediterranean rivers in the late 19th century were analysed to help to describe the native distribution of these species. All the individuals studied carried native haplotypes, the geographic distribution of which is consistent with published data. These results indicate that museum specimens from the 19th century could represent an opportunity to get a picture of the original genetic diversity distribution of this species complex.

Karyological characterization of the endemic Iberian rock lizard, Iberolacerta monticola (Squamata, Lacertidae): insights into sex chromosome evolution.

Rock lizards of the genus Iberolacerta constitute a promising model to examine the process of sex chromosome evolution, as these closely related taxa exhibit remarkable diversity in the degree of sex chromosome differentiation with no clear phylogenetic segregation, ranging from cryptic to highly heteromorphic ZW chromosomes and even multiple chromosome systems (Z1Z1Z2Z2/Z1Z2W). To gain a deeper insight into the patterns of karyotype and sex chromosome evolution, we performed a cytogenetic analysis based on conventional staining, banding techniques and fluorescence in situ hybridization in the species I. monticola, for which previous cytogenetic investigations did not detect differentiated sex chromosomes. The karyotype is composed of 2n = 36 acrocentric chromosomes. NORs and the major ribosomal genes were located in the subtelomeric region of chromosome pair 6. Hybridization signals of the telomeric sequences (TTAGGG)n were visualized at the telomeres of all chromosomes and interstitially in 5 chromosome pairs. C-banding showed constitutive heterochromatin at the centromeres of all chromosomes, as well as clear pericentromeric and light telomeric C-bands in several chromosome pairs. These results highlight some chromosomal markers which can be useful to identify species-specific diagnostic characters, although they may not accurately reflect the phylogenetic relationships among the taxa. In addition, C-banding revealed the presence of a heteromorphic ZW sex chromosome pair, where W is smaller than Z and almost completely heterochromatic. This finding sheds light on sex chromosome evolution in the genus Iberolacerta and suggests that further comparative cytogenetic analyses are needed to understand the processes underlying the origin, differentiation and plasticity of sex chromosome systems in lacertid lizards.

Genome duplication in early vertebrates: insights from agnathan cytogenetics.

Agnathans represent a remnant of a primitive offshoot of the vertebrates, and the long evolutionary separation between their 2 living groups, namely hagfishes and lampreys, could explain profound biological differences, also in karyotypes and genome sizes. Here, cytogenetic studies available on these vertebrates were summarized and data discussed with reference to the recently demonstrated monophyly of this group and to the 2 events of whole genome duplication (1R and 2R) characterizing the evolution of vertebrates. The comparison of cytogenetic data and phylogenetic relationships among agnathans and gnathostomes seems to support the hypothesis that 1R and 2R occurred before the evolutionary divergence between jawless and jawed vertebrates.

Isolation of novel microsatellite loci in the black goby Gobius niger and cross-amplification in other gobiid species (Perciformes, Gobiidae).

Twelve microsatellite loci were isolated from and characterized for the black goby Gobius niger. These loci were tested on a total of 48 individuals from two geographically distant locations (Orbetello and Cattolica) and the number of alleles ranged from two to 18, with expected (H(e)) and observed (H(o)) heterozygosities ranging from 0.042 to 0.941 and from 0.042 to 0.917, respectively. The loci described were used to cross-amplify other gobiid species belonging to Gobius, Zosterisessor, Lesueurigobius and Aphia.

Characterisation of a GC-rich telomeric satellite DNA in Eumeces schneideri Daudin (Reptilia, Scincidae).

A hitherto undescribed satellite DNA family (AvaII satDNA) has been isolated and characterised in Eumeces schneideri, a squamate reptile belonging to the family Scincidae. AvaII satDNA is characterised by a monomer length of 208 bp, a GC content of 59% and exhibits a certain degree of CpG methylation. FISH experiments with AvaII satDNA probe produced bright signals (i) at the end of the short arms of all subtelocentric chromosomes except for pair 14, in which the signal was at the end of the long arms, (ii) at the ends of both arms of the small metacentric chromosomes 12, and (iii) in a terminal position on the acrocentric chromosomes 11 and 13. AvaII satDNA repeats were not found in the metacentric pair 3, whereas only a weak interstitial signal occurred in the metacentric pairs 1 and 2. C-banding showed that this satellite represents most of the constitutive heterochromatin in the genome of this skink, and chromomycin A(3) staining produced a clear signal overlapping with the satellite, except for NOR-associated heterochromatin. In addition, quantitative dot blot analysis showed that these repetitive sequences constitute about 3% of the genomic DNA of this lizard. AvaII satDNA sequence analysis revealed the occurrence of short guanine residue stretches for which a function in structural stability of these sequences and a role in recombination with telomeric sequences can be hypothesised. Fibre FISH experiments showed that on some chromatin fibres telomeric sequences and AvaII satellite DNA repeats are intermingled or overlapping.

Chromosomal study of native and hatchery trouts from Italy (Salmo trutta complex, Salmonidae): conventional and FISH analysis.

A cytogenetic analysis was carried out using conventional staining, banding techniques and fluorescence in situ hybridization (FISH) in Italian populations of brown trout (Salmo truttacomplex). All individuals analysed, belonging to the Atlantic (At), Marmoratus (Ma), Adriatic (Ad) and Mediterranean (Me) lineages, showed remarkable karyotype uniformity, with diploid complement of 2n = 80 chromosomes, arm number (NF) of 102 and invariable karyotype composition. Such uniformity was also observed with respect to the location of 5S rDNA and the active, i.e. silver-positive NOR sites. On the contrary, FISH with 28S ribosomal probe and fluorescent staining with CMA3 revealed that inactive NOR sites are more numerous in Ad and Me than in At and Ma lineages. A centromeric sequence was successfully isolated from Salmo trutta individuals by polymerase chain reaction (PCR)-based cloning, using primers designed from published Atlantic salmon (Salmo salar) satellite DNA sequences. This sequence had high AT content (65.3%) and short consensus motif (A/T)(G/C)AAA(T/C) similar to other centromeric satellite repeats. The isolated satellite DNA clones were localized with FISH in the centromeric regions of the brown trout chromosomes, showing lineage-specific patterns. Because it is well known that AT-rich sequences can induce a pronounced DNA curvature, which in turn would promote faster and higher chromatin spiralization, it may be hypothesised that the wide distribution of this satellite in the S. trutta genome may have played a role in its karyotype stability. The presence of this sequence in other salmonid species was also tested by Southern blot hybridization and used to analyze its evolution within salmonids.

Mitochondrial DNA variation of an isolated population of the Adriatic brook lamprey Lampetra zanandreai (Agnatha: Petromyzontidae): phylogeographic and phylogenetic inferences.

Two mitochondrial genes were examined to compare an isolated population of the Adriatic brook lamprey Lampetra zanandreai in central Italy with other populations in the species range (Po plain) and with parasitic and freshwater lampreys. A single haplotype, identical to one in a Venetian sample, was found in 10 individuals from the isolated population. The reduced variability is consistent with a history of dispersal after the Pleistocene expansion of the Po basin. The results support the hypothesis of an origin of L. zanandreai and L. fluviatilis-L. planeri from a common anadromous ancestor.

The chromosomal complement of the artedidraconid fish Histiodraco velifer (Perciformes: Notothenioidei) from Terra Nova Bay, Ross Sea.

The karyotype of Histiodraco velifer from the Antartic Ocean was analyzed using various banding methods and in situ hybridization with a telomeric probe. A male and a female had a diploid set of 46 chromosomes (6 submetacentric + 40 acrocentric, FN = 52); the nucleolar organizer was CMA3-positive and was located on the short arm of a medium-sized submetacentric pair. All chromosomes stained uniformly with DAPI, whereas C-banding revealed heterochromatic blocks that were mostly located centromerically and telomerically and were resistant to ALUI digestion. The substantial identity of the karyotype of H. velifer with that of the other artedidraconids investigated so far suggests that chromosome changes must have played a less than significant role in the speciation among the lineages of this fish family endemic to Antarctica.

Chromosome banding and molecular cytogenetic study of two Mediterranean trachinoid fish species (Teleostei: Trachinidae, Uranoscopidae).

The chromosomes of Echiichthys vipera (Trachinidae) and Uranoscopus scaber (Uranoscopidae) were analyzed by means of various banding methods and fluorescence in situ hybridization (FISH) with telomeric and major rDNA probes, respectively. The karyotype of E. vipera was composed of 48 acrocentric chromosomes and NOR sites, as revealed by all detection methods, were situated pericentromerically on a single pair of middle-sized chromosomes. Blocks of constitutive heterochromatin were present in the pericentromeric regions of all pairs of chromosomes. The karyotype of U. scaber showed three karyomorphs: 2n = 30 (18 m + 12 a/st [m = metacentric, a = acrocentric and st = subtelocentric]), 2n = 28 (20 m + 8 a/st), 2n = 27 (21 m + 6 a/st). NORs, as revealed by FISH, were situated pericentromerically on a single pair of middle-sized chromosomes in spite of Ag-positive signals in the centromeres of all pairs of chromosomes. Robertsonian fusions were hypothesized for observed variation due to invariable number of chromosome arms FN = 48.

Chromosomal studies on ten species of notothenioid fishes (Notothenioidei: Bathydraconidae, Channichthyidae, Nototheniidae).

The results of a cytogenetic study conducted with banding and in situ hybridization techniques using ribosomal and telomeric probes on various species belonging to three families (Bathydraconidae, Channichthyidae and Nototheniidae) of the perciform suborder, Notothenioidei, are reported. The heterochromatin distribution and composition, nucleolar organiser and localisation of telomeric sequences seem to indicate that both in karyologically conservative families such as channichthyids and in families exhibiting greater karyological variability, certain DNA fractions like ribosomal genes and centromeric and telomeric DNAs are prone to some variability. This could play an important role in favouring or hampering chromosome rearrangements.

Cytogenetics of nine species of mediterranean blennies and additional evidence for an unusual multiple sex-chromosome system in Parablennius tentacularis (Perciformes, Blenniidae).

The chromosomal complements of nine species of Blenniidae (Aidablennius sphylnx, Blennius ocellaris, Lypophris adriaticus, L. pavo, L. trigloides, Parcablennius gattorugine, P. ponticus, P. sanguinolentus, P. tentacularis) from the Adriatic Sea were analysed with several banding methods and in-situ hybridization. In all species, the diploid set consists of 48 mostly acrocentric chromosomes and has a similar location (terminal centromeric) of NORs, except for L. pavo (interstitial pericentric) and P. ponticus (terminal on the long arm). There are major differences in karyotype with regard to the amount and distribution of heterochromatin. Parablennius tentacularis shows a distinctive sex-chromosome system involving 2n = 48 males with a large totally heterochromatic Y chromosome, and males with 2n = 47. This difference is likely to be the consequence of a translocation of an autosome on the original Y. This finding constitutes an additional instance of the great variability in origins of multiple sex chromosome systems in vertebrates.