Karyotype differentiation between two species of carangid fishes,genusTrachurus (Perciformes: Carangidae)

A karyological study ofTrachurus trachurus andT. mediterraneus (Perciformes: Carangidae) was conducted by standard, fluorochrome staining (CMA₃, mithramycin, quinacrine mustard, DAPI), C-, Ag-NOR, and Alu-I banding methods. The karyotypes of both species consisted of 2n = 48 chromosomes, but of different FN:T. trachurus possessed a chromosome complement of 2 metacentric and 46 acrocentric elements, fundamental number (FN) = 50 andT. mediterraneus, a chromosome complement of 4 metacentric, 4 submetacentric, 14 subtelocentric and 26 acrocentric chromosomes, FN = 70. In neither of the two taxa investigated were heteromorphic sex chromosomes observed. The nucleolar organizer region was interstitially located on the long arm of the Ist pair of chromosomes in both species, intermediate inT. mediterraneus and subterminal inT. trachurus. Constitutive heterochromatin was found in nearly all centromeric and telomeric regions inT. trachurus; inT. mediterraneus it formed less intense telomeric and centromeric bands and thin interstitial bands on eight chromosome pairs. In addition, the C-positive material reacted differently to the digestion with endonuclease Alu-l in the two species. The results are discussed and compared with karyological data known for other species of Carangidae.     

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.     

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.     

Chromosomal complements of two forms of Neanthes japonica (Polychaeta,Nereididae) with evidence of male-heterogametic sex chromosomes

Karyotypes of the brackish-water polychaeteNeanthes japonica (Izuka) collected from five rivers in Japan from 1984 to 1988 were examined with air-drying and flame-drying methods using materials consisting of regenerating tails, clumps of spermatogonia and youngN. japonica specimens (embryos, larvae or juveniles). A diploid number of 28 was determined in well-spread metaphase chromosomes of mitotic cells. The presence of an XX-XY (male heterogametic) sex chromosome system was established for the first time in polychaetes. The Y chromosome was larger than the X chromosome. Slight differences in karyotype were found between two forms (the small- and large-egg forms), which are very similar in adult morphology but can be distinguished by reproductive and developmental characteristics.     

Structural chromosomal polymorphism in the dog-whelk Nucella lapillus (Mollusca: Neogastropoda)

On the English and French Channel coasts, the dog-whelk Nucella lapilus (L.) exhibits variation in chromosome number which appears to correlate with the degree of wave action on the shore. The more common, 2n=26 morph is typically found on exposed shores subjected to a high degree of wave action, whereas those with higher chromosome numbers, up to the recorded maximum of 2n=36, are restricted to more sheltered environments. The polymorphism is thought to be Robertsonian in nature, involving centric (centromere) fission or fusion, but detailed analysis of the polymorphism has been restricted by lack of success in labelling individual chromosomes. Using a silver-staining technique for the nucleolar organiser regions (NORs), three pairs of chromosomes, in the basic 2n=26 karyotype, have been positively identified. A series of structural chromosomal rearrangements (pericentric and paracentric inversions) affecting one pair of chromosomes involved in the numerical polymorphism is described. Significant differences exist between populations with respect to this character. These chromosomal rearrangements have the potential to reduce the level of interbreeding between the different types, and may act as isolating mechamisms between breeding groups. Structural chromosomal polymorphism is likely, therefore, to have greater significance in relation to adaptation than simple numerical variation. This finding raises important questions concerning the (cyto)taxonomic status of N. lapillus in different parts of its range.     

Spermatocyte chromosome banding studies inBuccinulum corneum (Prosobranchia: Neogastropoda): Variation in silver-NOR banding pattern

Diploid number (2n=72), and haploid number (n=36) forBuccinulum corneum (L. 1758) collected from the Gulf of Palermo in December 1987 were determined. A simple method to obtain nucleolar organizer regions (NOR), and constitutive heterochromatin regions (C-bands) of chromosomes ofB. corneum is described. Analyses of silver-stained chromosome preparations ofB. corneum suggest that a within-individual variability in NOR-banding pattern is present in each of the five specimens analysed.     

云南高黎贡山白颌大角蟾的核型,C—带及Ag—NORs的研究

比较了云南高黎贡山地区的贡山独龙江和腾冲大蒿坪白颌大角蟾（Megophryslateralis）两个地理种群的核型、C-带和Ag-NORs结果表明,两个地理种群在核型和带型上都有差异两个地理种群的核型均为2n＝26,NF＝52染色体形态差异不明显,而次缢痕的位置完全不同,贡山独龙江标本的次缢痕位于No．2的长臂上近着丝点处,腾冲标本的次缢痕位于No．5的短臂上近着丝点的部位在腾冲标本中发现一雄性个体中有一条额外的染色体,可能是B染色体两地标本的C-带差异不太显著,贡山独龙江标本的C-带相对较为显著．贡山独龙江标本的Ag-NORs位于No．2长臂近着丝点处,与次缢痕的部位对应,两条同源染色体上大小有显著差异．腾冲标本的Ag-NORs位于No．5短臂上近着丝点处,与次缢痕的部位对应依据核型和带型的比较,对白颌大角蟾的分类和进化问题进行了讨论。     

Karyotype and sex determination in <Emphasis Type="Italic">Dinophilus gyrociliatus</Emphasis> (Polychaeta: Dinophilidae)

The study of the male and female karyotypes of the polychaete Dinophilus gyrociliatus was performed with the aim of ascertaining the diploid number of chromosomes and confirming the existence of karyological differences between the two sexes. Our results evidenced that the female karyotype of D. gyrociliatus consists of 2n=24 chromosomes, while the male karyotype has 2n=23 chromosomes. X chromosomes are subtelocentric and much bigger than the autosomes. The size of the D. gyrociliatus chromosomes, which in the female embryos vary in length from little more than 2.8 wm to less than 0.7 wm, are relatively small by comparison with those of other polychaetes. The existence of maternal and environmental factors able to influence the sex ratio of D. gyrociliatus and chromosomal differences between the sexes confirms that: (1) sex determination is chromosomal and syngamic of the XX-X0 type and (2) control of the sex ratio is progamic and depends on genetic and environmental factors.     

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     

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 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     

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.     

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.     

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.     

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.     

团花锦蛇、绿锦蛇和三索锦蛇的核型及Ag-NORs

报道了锦蛇属团花锦蛇（Ｅ．ｄａｖｉｄｉ）、绿锦蛇（Ｅ．ｐｒｖｓｉｎａ）和三索锦蛇（Ｅ．ｒａｄｉａｔａ）３个种的核型和Ａｇ－ＮＯＲｓ,团花锦蛇的型２ｎ＝３６（８Ｖ＋６ｓＶ＋２Ｉ＋２０Ｍ）,绿锦蛇的核型２ｎ＝３６（７Ｖ＋７ｓＶ＋２Ｉ＋２０ｍ）,三索锦蛇的核型２ｎ＝４０（６Ｖ＋３ｓＶ＋２ｓＩ＋５Ｉ＋２４ｍ）;①团花锦蛇和绿锦蛇的染色体数目和结构与此属大多数咱的相似,;②此种为雄性,未见染色体异型。③Ａｇ     

Influence of social factors on sex ratio at birth,maternal investment and young survival in a prosimian primate

Summary In order to determine whether social factors influence sex ratio at birth in lesser mouse lemurs, experiments were conducted during 5 successive breeding periods on 51 females. At the beginning of the breeding season, females were either isolated (I) or grouped (G) in heterosexual groups with an increasing number of females (2, 3 or 4). To ensure mating, I females were introduced in a group only during the oestrous period. After mating, both I and G females were isolated during pregnancy and lactation. Reproductive capacities of females in terms of oestrus occurrences (n = 324), impregnations (n–210), pregnancies (n = 136) or abortions (n = 38) or litter sizes (1–3 young) were affected neither by age and parity of females nor by group housing prior to conception. G females produced significantly more sons than daughters (67% males for 189 newborn) while females living alone except during the mating period demonstrated a significant inverse tendency (39.6% males for 96 newborn). Distribution of sexes in litters was statistically different from random and varied according to the shift of sex ratio at birth. In G females, the shift in the sex ratio towards males was consistent across the different groups, independent of the number of females living together, suggesting that the presence of only 1 female is sufficient to induce a bias in the sex ratio. No correlation was found between infant survival at weaning and age, parity or group housing of the mother. The maternal investment allocated to male or female newborn was similar provided the litter contained at least 1 male. In litters without males, growth and survival of female infants were significantly less. These results on sex ratio bias in captive female mouse lemurs agree with directions of bias predicted by the local resource competition model for facultative sex ratio adjustment (Clark 1978). Nevertheless, the pattern observed in mouse lemurs appears to be independent of the nutritional state of the female and of differential maternal investment.     

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     

Karyotypes in two species of the genusHippocampus (Pisces: Syngnatiformes)

Diploid modal numbers of chromosomes 2n=48 forHippocampus ramulosus and 2n=44 forH. hippocampus, collected in the Gulf of Palermo in May 1985, are established. No sex-linked heteromorphic pairs are observed in the two species analyzed. The karyotype ofH. hippocampus seems to be a derived condition.     

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