Karyology of the toadfish Porichthys plectrodon (Jordan and Gilbert, 1882) (Batrachoididae) from Margarita Island,Venezuela

This paper reports the results of cytogenetic analyses carried out on Porichthys plectrodon using conventional Giemsa staining, C-banding and silver staining techniques. A diploid chromosome count of 2n=44 was observed, consisting of 8 metacentric, 10 submetacentric, 6 subtelocentric and 20 acrocentric chromosomes. Differences in length made it possible to identify homologous chromosomes within the metacentric group. Constitutive heterochromatin was distributed as large pericentromeric blocks in pairs 1 and 2, while the rest of the chromosomes were marked in centromeric regions, some more conspicuously than others. One pair of small-sized acrocentric NOR-bearing chromosomes (21) was identified by the nucleolar regions located terminally on their short arms.Communicated by P.W. Sammarco, Chauvin     

Cytogenetic analysis of Epinephelus marginatus (Pisces: Serranidae), with the chromosome localization of the 18S and 5S rRNA genes and of the (TTAGGG)n telomeric sequence

 A cytogenetic analysis was carried out on specimens of Epinephelus marginatus (Lowe, 1834) from three localities in the Mediterranean Sea, to deepen knowledge of the chromosome complement of the species and identify any possible population-specific cytogenetic markers. All specimens had a 2n = 48 acrocentric karyotype with two Ag-, chromomycin A₃- and C-positive NORs (nucleolar organizer regions) in the subcentromeric region of the smallest chromosome pair. The constitutive heterochromatin was distributed centromerically. Except for NORs, neither eu- nor heterochromatin show fluorescence after fluorochrome staining, i.e. there is no localized increase of AT- or GC-rich DNA. In all populations, the (TTAGGG) _n telomeric sequences are restricted to the telomeres, and the 18S and the 5S rDNA clusters are located on different chromosome pairs. In specimens from Sardinia, additional signals after C-banding, Ag-staining and FISH (fluorescence in situ hybridization) with 18S rDNA can be observed in the telomeric region of one or two large-sized chromosomes, classified as No. 2. This suggests that additional and variable NORs could be detected in the species in addition to those on the genus-specific, NOR-bearing Chromosome Pair 24. Received: 20 October 1999 / Accepted: 14 April 2000     

Cytogenetic studies in green mussel, Perna viridis (Mytiloida: Pteriomorphia), from West Coast of India

Chromosomes of Perna viridis were characterized by karyotype analysis, C-banding and nucleolus organizer regions (NORs). The diploid chromosome number was confirmed as 30 and the karyotype is composed of ten metacentric and five submetacentric chromosome pairs. Constitutive heterochromatin blocks were found on all chromosomal pairs except chromosomal pair 15, which showed uniform staining throughout the entire chromosomes. Silver staining revealed nucleolus organizer regions on telomeric region of four chromosomal pairs, viz. 1, 3, 7 and 11. This is the first comprehensive study undertaken on chromosomes of Perna viridis.     

Karyotypic characterization of the great sturgeon, Huso huso, by multiple staining techniques and fluorescent in situ hybridization

A karyotype analysis by several staining techniques was carried out on the great sturgeon, Huso huso (Linnaeus, 1758). The karyotype (2n = 118 ± 2) was composed of 42 pairs of meta-/submetacentric chromosomes and 17 pairs of acrocentrics/microchromosomes. Constitutive heterochromatin was mainly located at the centromeric regions of the acrocentric chromosomes. The biarmed chromosomes showed weak C-bands. Fluorescent staining with GC-specific chromomycin A₃ showed clearly recognizable fluorescent regions, whereas a more uniform base composition was revealed by the AT-specific 4,6-diamidino-2 phenylindole. After Ag-staining, nucleolar organizer regions could be observed on the short arms of two medium-sized submetacentrics and on two acrocentrics. Digoxigenated 28S and 5S rDNA probes, prepared from Acipenser naccarii DNA and hybridized to metaphase chromosomes, showed signals on six and two chromosomes, respectively. The telomeric sequence (TTAGGG) _n detected by FISH was located at both ends of each chromosome. Results are discussed in relation to karyotype organization and evolution in sturgeons. Received: 1 April 1998 / Accepted: 21 July 1998     

Cytogenetic analysis of Oedalechilus labeo (Pisces: Mugilidae), with a report of NOR variability

 A cytogenetic analysis by several staining techniques was carried out on Oedalechilus labeo specimens from the west coast of Italy, in order to extend the karyological knowledge on Mediterranean mullets. The karyotype of the species is composed of 46 acrocentric and 2 subtelocentric chromosomes. Constitutive heterochromatin was found to be restricted to the centromeres. Fluorochrome staining revealed a uniform base composition along the chromosome arms. Nucleolus organizer regions (NORs) are located on the short arms of chromosome pair 9 and can be either homomorphic or quite heteromorphic in size. In some specimens chromomycin A₃-staining and fluorescence in situ hybridization with 18S rDNA revealed a third additional and inactive NOR on the short arms of a medium-sized chromosome. This is the first report of NOR variability in Mugilidae, a family generally characterized by a quite conservative karyotype. Heterochromatin composition and NOR location differentiate O. labeo from a cytotaxonomical point of view from the Liza species studied, Liza being considered the genus from which the genus Oedalechilus derived. Received: 10 April 1999 / Accepted: 21 October 1999     

安徽沿江地区4种蛇的染色体组型、C带和Ag-NORs研究

本文报道游蛇亚科４种蛇的核型、Ｃ带和ＡｇＮＯＲｓ,结果：黄链蛇２ｎ＝４６．虎斑游蛇２ｎ＝４０,第４号染色体（Ｎｏ．４）有随体．鸟梢蛇和紫灰锦蛇２ｎ＝３６,鸟梢蛇的Ｎｏ．５短臂近着丝粒区有一次缢痕．虎斑游蛇Ｎｏ．５为性染色体,其余３种的性染色体为Ｎｏ．４．这４种蛇均为ＡＦ＝５０;Ｃ带型的种属性特征明显,其中紫灰锦蛇的端粒型Ｃ带特别发育,其余三种以着丝粒Ｃ带较发达．黄链蛇、虎斑游蛇和紫灰锦蛇的Ｗ染色体Ｃ带正染呈现整条异染色质化;银染结果４种蛇均只显示一对ＮＯＲｓ,但其分布不同,其中虎斑游蛇ＮＯＲｓ呈异态现象．文章讨论了核型的演化和次缢痕、ＮＯＲｓ及Ｃ带的关系     

Karotypic characterization of turbot (Scophthalmus maximus) with conventional,fluorochrome and restriction endonuclease-banding techniques

A karyotypic analysis was carried out in turbot (Scophthalmus maximus) using conventional banding techniques, fluorochromes and restriction endonucleasebanding. The standard karyotype of turbot is 2n=44 chromosomes, with 48 chromosome arms. Nucleolar organizer regions, which were localized in the short arm of Chromosome Pair No. 3, showed C-and chromomycin A₃-positive staining. C-bands were mainly located at the centromeres, but were also present in some interstitial and telomeric locations. No differences were revealed among constitutive heterochromatin bands after treatment of fixed chromosomes with fluorochrome staining and restriction endonucleases. Digestion with DdeI restriction enzyme produced a pattern of interstitial banding which suggested some degree of differentiation along the chromosome arms in turbot. Neither variation in chromosome number of arm number nor polymorphism in nucleolar organizer regions was revealed in the turbot analyzed.     

Karyotype, nucleolus organiser regions and constitutive heterochromatin in Ostrea angasi (Molluscae: Bivalvia): evidence of taxonomic relationships within the Ostreidae

Chromosome preparations from gill tissue of the Australian flat oyster Ostrea angasi Sowerby were studied with conventional Giemsa staining, C-banding and silver staining techniques. A diploid complement of 2n = 20 was observed, consisting of five metacentric, three submetacentric and two subtelocentric pairs. Constitutive heterochromatin was distributed as large centromeric blocks in Chromosome Pairs 3, 6, 8, 9 and 10. The nucleolus organizer regions (NORs) were located terminally on long arms of Chromosome Pairs 9 and 10. This allowed the identification of homologous chromosomes in submetacentric and subtelocentric pairs. Intraspecific variability in NOR pattern as revealed by differences in the number of silver-stained NORs (Ag-NORs) per cell was found to be very common. Comparison of the patterns of karyotype, C-band and Ag-NORs between species of the larviparous oysters for which data have been published demonstrate that the chromosomal structure of the endemic Australian and New Zealand species O. angasi shows little similarity to the Southern Hemisphere oysters O. (Eostrea)puelchana Orbigny and Tiostrea chilensis (Philippi) and the Indo-West Pacific oyster O. denselamellosa, but very high resemblance to the European species O. edulis. Received: 12 August 1996 / Accepted: 16 September 1996     

Replication,C and Ag-NOR chromosome-banding in two anguilliform fish species

The chromosomes of the Conger conger and Echelus myrus (Anguilliformes: Teleostei), were analysed by conventional (C and Ag-NOR) and by replication-banding techniques. Both species had a diploid number of 38 and one chromosome pair with C-positive nucleolar organizer regions (NOR). These cytogenetic traits are mainly consistent with those recorded for anguilliform species in general. The replication-banding pattern allowed us to identify individual chromosome pairs, to detect different classes of chromatin, and to suggest chromosome evolutive mechanisms in these two species. The results confirm the superiority of replication patterns in resolving longitudinal differentiation of fish chromosomes, that is not generally possible from structural bands.     

Cytogenetics in the sacoglossan Oxynoe olivacea (Mollusca: Opisthobranchia): karyotype, chromosome banding and fluorescent in situ hybridization

Developing embryos and sexually mature follicles of the male portion of ovotestis proved to be a suitable material as a source of cleaving cells for advanced cytological investigations on the sacoglossan species Oxynoe olivacea Rafinesque, 1819 (Mollusca: Opisthobranchia). O. olivacea has a diploid chromosomal number of 30 made up of 15 pairs of which six are metacentric/submetacentric (M/SM), four subtelocentric (ST) and five on the borderline between SM and ST. Correspondingly, 15 bivalents occur in spermatocytes at Metaphase I. Constitutive heterochromatin is scarce and restricted to small C-bands seen in five pachytene bivalents. The use of combined silver staining and fluorescent in situ hybridization (FISH) with a Paracentrotus lividus (Echinodermata) 4.3 kilobase (kb) rDNA probe (prR14) consisting of sequences from the 3′ end of 18S rDNA to the 3′ end of 26S rDNA, revealed that nucleolus organizer regions (NORs) are situated terminally on one arm of a small metacentric pair. The telomeric (TTAGGG) _n sequence did not hybridize with termini of O. olivacea chromosomes. Received: 14 December 1999 / Accepted: 10 July 2000     

Genetic divergence among three sympatric species of Mediterranean Patella (Archaeogastropoda)

Patella caerulea L., P. aspera Lam. (=P. ulyssiponensis Gmelin). P. rustica L. (=P. lusitanica Gmelin) are coexisting Mediterranean species of the genus Patella. P. caerulea and P. rustica have a haploid complement of n=9 with seven metacentric and two telocentric chromosomes, while P. aspera has a haploid complement of n=8 without telocentric chromosomes. To better define the phylogenetic relationships among these three species, an electrophoretic analysis of 12 enzyme coding loci was performed on samples of the three species collected from Laigueglia (Liguria, Italy) in 1989. On the whole, genotypic frequencies were in agreement with Hardy-Weinberg expectations and no significant differences were observed among the populations of the three species as far as their genetic structure is concerned. Nearly 50% of the sampled loci were diagnostic. Nei's genetic distance was 0.82 between P. caerulea and P. aspera, 0.97 between P. aspera and P. rustica and 0.94 between P. caerulea and P. rustica. By greatly separating P. rustica from the other two species, results of the electrophoretic analysis are consistent with the traditional view, which regards P. aspera and P. caerulea as more closely related than P. rustica on the basis of radular teeth morphology. Using genetic distances and the assumptions of the molecular clock, lineages leading to P. aspera and to P. caerulea may have diverged from the stem common to P. rustica ca. 18 million years ago.     

Le caryotype d'Aulacomya ater regia (Mollusca: Bivalvia: Mytilidae) des Iles Kerguelen

In 1983, specimens of the antarctic mussel Aulacomya ater regia Powell, 1957 were collected from the Kerguelen Islands and transported alive to the Zoological Station in Villefranche-sur-Mer, France. The chromosome complement of the mussel, as determined from branchial tissue, was found to consist of 13 pairs of chromosomes with terminal or subterminal centromeres. This species differs from the other species of Mytilidae studied up to the present in the number and the morphology of the chromosomes. A. ater regia is also unique among the known bivalves in displaying only terminal or subterminal centromeres.     

Phylogenetic relationships of deep-sea mussels of the genus<Emphasis Type="Italic"> Bathymodiolus</Emphasis> (Bivalvia: Mytilidae)

We examined phylogenetic relationships among three Bathymodiolus species in Japanese waters and Bathymodiolus spp. from the Manus Basin by two different approaches. Two-dimensional gel electrophoresis allowed us to compare 263–407 (average=318) proteins, giving comprehensive information on genetic distances among the species. The neighbor-joining tree presented two clusters: (1) B. japonicus and B. platifrons and (2) B. septemdierum and B. sp. Members of the first cluster contain methanotrophic endosymbiotic bacteria and members of the second cluster contain thioautotrophic endosymbionts. DNA sequencing of a fragment (415 bp) of mitochondrial cytochrome c oxidase subunit I (COI) provided a neighbor-joining tree with the same topology as that derived from protein analysis. Inspection of intraspecific variation in COI in B. japonicus and B. platifrons revealed no genetic differentiation between mussel populations of either species from cold-water seeps versus hydrothermal vents, suggesting high adaptability of these Bathymodiolus species to deep-sea chemosynthetic environments. Our results indicated genetic exchanges between mussels from distant localities, suggesting that a limited dispersal capability of the larvae is not the likely factor leading to speciation events in these Bathymodiolus species.Communicated by T. Ikeda, Hakodate     

Highly repeated DNA sequences in the scleractinian coral genusAcropora: Evaluation of cloned repeats as taxonomic probes

A plasmid clone containing highly repeated DNA sequence fromAcropora formosa was used to probe slot blots of genomic DNA and Southern blots of Taq I digests from other Acroporidae. Homologous repeated DNA sequences were detected in 12 otherAcropora species, but not in three other species of Acroporidae (Astreopora sp.,Montipora digitata andM. aequituberculata). Slot-blot experiments indicated that the repeated sequences inAcropora latistella, A. tenuis, A. longicyathus andA. nobilis were distantly homologous with the clonedA. formosa repeat, whereas those inA. pulchra, A. millepora, A. valida, A. hyacinthus andA. microphthalma were highly homologous with this probe and those inA. digitifera were intermediate. Relatedness of the highhomology group toA. formosa was assessed by comparison of Taq I-digestion patterns. The predominant repeats inA. pulchra andA. hyacinthus had two Taq I sites per repeat unit (as didA. formosa), whereas repeats inA. digitifera, A. valida andA. microphthalma had one Taq I site per repeat; the pattern given byA. millepora implied that its highly homologous repeat units contained either one or two Taq I sites. Within the high-homology group, decreasing number of Taq I sites implies increasing taxonomic distance fromA. formosa. The relatedness series implied by these data differs from that based on morphological criteria.     

Multiple sex-chromosome system and other karyological characterizations of Pterotrachea hippocampus (Mollusca: Mesogastropoda)

Two modal diploid numbers of chromosomes were found for Pterotraches hippocampus Philippi (Mollusca: Mesogastropoda) collected from the Gulf of Palermo in 1990: 2n=31 and 32 for males and females, respectively. This, along with other karyological characteristics such as the occurrence of a trivalent configuration at diakinesis and two types of metaphase-II spreads in spermatocytes, supports the notion that a X₁X₂Y/X₁X₁X₂X₂ sex mechanism operates in the species investigated here. Silver nitrate procedure revealed an intraindividual variation in the Ag-staining pattern occurring in this species. The majority of the chromosome pair displayed terminal and/or interstitial heterochromatic blocks after C-banding.     

Activities of metabolic enzymes in the deep-water crabsChaceon fenneri andC. quinquedens and the shallow-water crabCallinectes sapidus

The activities of 18 enzymes were measured in gill, hepatopancreas and muscle tissue of the deep-water crabsChaceon fenneri andC. quinquedens and the shallow-water crabCallinectes sapidus collected from the Gulf of Mexico in January 1989. The activities of catabolic enzymes were correlated in general with the known metabolic rates of the three species. Activities were much higher inC. sapidus than inChaceon fenneri andC. quinquedens. In some cases,C. quinquedens had higher activities thanC. fenneri. The activities of enzymes of amino acid metabolism (glutamate dehydrogenase and alanine aminotransferase) were higher inC. quinquedens, which had high hemolymph [ammonia] and ammonia excretion rates. The activity of lactate dehydrogenase (LDH) ofC. fenneri andC. quinquedens were correlated with the two species' abilities to withstand hypoxia. The more hypoxiatolerant species,C. quinquedens, had higher activity of LDH in its muscles than didC. fenneri.     

Karyotype analysis of the sea urchinParacentrotus lividus (Echinodermata): evidence for a heteromorphic chromosome sex mechanism

A consistent diploid number of 2n = 36 was determined for the sea urchinParacentrotus lividus from the Gulf of Palermo by analysis of mitotic chromosomes of both early developing embryos and male gonads. The haploid numbern = 18 was determined by counts of spermatocyte bivalents at diakinesis. A heteromorphic chromosome sex mechanism of the XY type is likely present in this species. This is indicated by the occurrence of a chromosomal pair, pair No. 2, which is heteromorphic in both morphology and size in about 50% of the mitotic figures (metaphases and anaphases) of einbryos. In addition, heteromorphism of the same pair of chromosomes occurred during spermatogonial metaphases in the five male specimens investigated here. The detection of a low chromosome number (2n = 36) compared to other echinoids (2n = 42 to 44), a heteromorphic chromosome sex system and the involvement of three chromosome pairs in nucleolar organization (NORs) provide evidence of the specialization of theP. lividus karyotype.     

Les caryotypes de quelques espèces de bivalves et de gastéropodes marins

The karyotypes of the bivalves Ostrea edulis (2 n=20), Crassostrea gigas (2 n=20), Mytilus galloprovincialis (2 n=28) and M. edulis (2 n=28) were obtained from mitotic metaphases of branchial tissue by means of a cellular suspension technique. The occurrence of metacentric, submetacentric and telocentric chromosomes in O. edulis as well as differences in size between Pair 1 and Pair 10 emphasize the cytological interest of this species compared to C. gigas which possesses only metacentric and submetacentric chromosomes. The variation in Pair 2, which is telocentric in M. galloprovincialis and metacencentric in M. edulis, has been observed for the first time and may support taxological separation of these two species. The karyotypes of the mesogastropods Rissoa ventricosa (2 n=32) and Littorina neritoides (2 n=34) were obtained from mitotic metaphases of gonadal tissue by the same technique. Sexual chromosomes were identified in the karyotypes of R. ventricosa. At the beginning of spermatogenesis, the gonad of L. neritoides shows both haploïd and polyploïd meïotic metaphases which correspond to typical (germinal cells) and atypical (nurse cells) forms, respectively.     

Divergence between populations of a monogamous polychaete with male parental care: Premating isolation and chromosome variation

Low dispersal and sexual selection are characteristic of the coastal polychaeteNereis acuminata Ehlers 1868 [also known asNereis arenaceodentata Moore 1903 andNereis (Neanthes) caudata Delle Chiaje 1841]. We assessed levels of premating isolation between populations of this polychaete. Four North American populations were used, two from the Atlantic and two from the Pacific. Worms from all sites (1) were collected in 1987 and 1988 from the same habitat type, (2) were morphologically similar and keyed out asN. acuminata, and (3) reproduced monogamously and exhibited male parental care, an extremely rare reproductive mode in marine invertebrates. There was no evidence from 10-min or 36-h trials of premating isolation between the two Pacific populations. Incomplete premating isolation was found between the two Atlantic populations. High aggression and non-pairing occurred in some 10-min trials between males and females. However, in 36-h trials males and females from the two Atlantic populations always paired to mate. Complete premating isolation was found between Atlantic and Pacific populations. During 10-min trials, males and females from different oceans often attacked and then avoided each other, and they never paired to mate. Nor did they pair to mate in longer, 36-h trials. One Pacific and one Atlantic population were compared for tolerance to cold temperature. Pacific individuals were less able to tolerate cold water than Atlantic individuals. Two Atlantic populations studied had karyotypes with 11 pairs of small acrocentric chromosomes (2n=22), while the two Pacific populations had nine pairs of large metacentric or submetacentric chromosomes (2n=18). Such extreme dissimilarity in karyotype was not expected considering the similarity in morphology, habitat, and reproductive mode. Results suggest strongly that the Atlantic and Pacific populations have been allopatric for a long time, and are different species.     

Karyotype analyses reveal inter-individual polymorphism and association of nucleolus-organizer-carrying chromosomes in Capros aper (Pisces: Zeiformes)

Three different karyomorphs with 2n=46, 2n=44 and 2n=42 for Capros aper (L., 1758) (Zeiformes) collected from the Gulf of Lion, near Banyuls-sur-Mer, France, in July 1990 were determined. Karyomorphs were characterized by the same arm number [Fundamental number (FN)=50], suggesting that chromosome variations are due to Robertsonian fusions. In somatic metaphase spreads stained with silver nitrate, nucleolus organizer regions (NORs) consistently occupied a terminal position on the short arms of two small submetacentric chromosomes. Ca. 30% of silver-stained metaphases in each specimen showed NOR chromosomes associated in pairs by their nucleolus organizer regions.