Chromosome evolution in the Salmonidae (Pisces): an update

The karyotypes of salmonid fishes including taxa in the three subfamilies Coregoninae, Thymallinae and Salmoninae are described. This review is an update of the (Hartley, 1987) review of the chromosomes of salmonid fishes. As described in the previous review, the karyotypes of salmonid fishes fall into two main categories based on chromosome numbers: the type A karyotypes have diploid numbers close to 80 with approximately 100 chromosome arms (2n = 80, NF = 100), and the type B karyotypes have diploid numbers close to 60 with approximately 100 chromosome arms (2n = 60, NF = 100). In this paper we have proposed additional sub categories based on variation in the number of chromosome arms: the A' type with NF = 110-120, the A" type with NF greater than 140, and the B' type with NF less than 80. Two modes of chromosome evolution are found in the salmonids: in the Coregoninae and the Salmoninae the chromosomes have evolved by centric fusions of the Robertsonian type decreasing chromosome numbers (2n) while retaining chromosome arm numbers (NF) close to that found in the hypothetical tetraploid ancestor so that most extant taxa have either type A or type B karyotypes. In the Thymallinae, the chromosomes have evolved by inversions so that chromosome arm numbers (NF) have increased but chromosome numbers (2n) close to the karyotype of the hypothetical tetraploid ancestor have been retained and all taxa have type A' karyotypes. Most of the taxa with type B karyotypes in the Coregoninae and Salmoninae are members of the genus Oncorhynchus, although at least one example of type B karyotypes is found in all of the other genera. These taxa either have an anadromous life history or are found in specialized lacustrine environments. Selection for increases or decreases in genetic recombination as proposed by Qumsiyeh, 1994 could have been involved in the evolution of chromosome number in salmonid fishes.     

Robertsonian polymorphism in plaice, Pleuronectes platessa L., and cod, Gadus morhua L., (Pisces Pleuronectiformes and Gadiformes)

Karyotypic analysis of plaice, Pleuronectes platessa L., and cod, Gadus morhua L., revealed that the chromosome numbers in both species vary but that chromosome arm numbers (NF) stay constant. The C-, Q- and R-banding patterns also confirmed that the population of plaice studied shows Robertsonian polymorphism. The tendency of reduction in chromosome number in fishes suggests that Robertsonian fusions play a role in karyotype evolution in fishes.     

湘华鲮(♂)×鲮鱼(♀)杂交一代与其双亲染色体组型的比较研究

三种鱼的二倍体数目完全相同,均为2n=50。三种鱼的核型差异较大,尤其是双亲间的组型在形态上有明显的差异。然而杂交一代的m、sm二组染色体的组型却十分接近母体,这二组的染色体数占了全部染色体总数的88%。杂交一代染色体组型中的st和t二组染色体虽与双亲有所不同,但与双亲中这二组染色体组型的差异来比要小一些。三种鱼的中期分裂相中,未曾发现带有随体的染色体,也未发现与性别有关的异型染色体的存在。       

Phylogenetic conservation of chromosome numbers in Actinopterygiian fishes

The genomes of ray-finned fishes (Actinopterygii) are well known for their evolutionary dynamism as reflected by drastic alterations in DNA content often via regional and whole-genome duplications, differential patterns of gene silencing or loss, shifts in the insertion-to-deletion ratios of genomic segments, and major re-patternings of chromosomes via non-homologous recombination. In sharp contrast, chromosome numbers in somatic karyotypes have been highly conserved over vast evolutionary timescales – a histogram of available counts is strongly leptokurtic with more than 50% of surveyed species displaying either 48 or 50 chromosomes. Here we employ comparative phylogenetic analyses to examine the evolutionary history of alterations in fish chromosome numbers. The most parsimonious ancestral state for major actinopterygiian clades is 48 chromosomes. When interpreted in a phylogenetic context, chromosome numbers evidence many recent instances of polyploidization in various lineages but there is no clear indication of a singular polyploidization event that has been hypothesized to have immediately preceded the teleost radiation. After factoring out evident polyploidizations, a correlation between chromosome numbers and genome sizes across the Actinopterygii is marginally statistically significant (p = 0.012) but exceedingly weak (R ² = 0.0096). Overall, our phylogenetic analysis indicates a mosaic evolutionary pattern in which the forces that govern labile features of fish genomes must operate largely independently of those that operate to conserve chromosome numbers.     

Mitochondrial cytochrome b Sequence Variation and Phylogenetics of the Highly Specialized Schizothoracine Fishes (Teleostei: Cyprinidae) in the Qinghai-Tibet Plateau

The complete 1140 bp mitochondrial cytochrome b sequences were obtained from 39 individuals representing five species of all four genera of highly specialized schizothoracine fishes distributed in the Qinghai-Tibet plateau. Sequence variation of the cytochrome b gene was surveyed among the 39 individuals as well as three primitive schizothoracines and one outgroup. Phylogenetic analysis suggested that the group assignment based on 1140 bp of the cytochrome b sequence is obviously different from previous assignments, and the highly specialized schizothoracine fishes (Schizopygopsis pylzovi, Gymnocypris przewalskii, G. eckloni, Chuanchia labiosa, and Platypharodon extremus) form a monophyletic group that is sister to the clade formed by the primitive schizothoracine fishes (Schizothorax prenanti, S. pseudaksaiensis, and S. argentatus). The haplotypes of Schizopygopsis pylzovi and G. przewalskii were paraphyletic based on cytochrome b data, which most likely reflected incomplete sorting of mitochondrial DNA lineages. The diploid chromosome numbers of Schizothoracinae were considered in phylogenetic analysis and provided a clear pattern of relationships. Molecular dating estimated for highly specialized schizothoracine fishes suggested that the highly specialized schizothoracine fishes diverged in the late Miocene Pliocene to Pleistocene (4.5 × 10⁴–4.05 × 10⁶ years BP). The relationship between the cladogenesis of highly specialized schizothoracine fishes and geographical events of the Qinghai-Tibet plateau is discussed.     

Genetic and morphology analysis among the pentaploid F1 hybrid fishes (Schizothorax wangchiachii ♀ × Percocypris pingi ♂) and their parents

Triploid and pentaploid breeding is of great importance in agricultural production, but it is not always easy to obtain double ploidy parents. However, in fishes, chromosome ploidy is diversiform, which may provide natural parental resources for triploid and pentaploid breeding. Both tetraploid and hexaploid exist in Schizothorax fishes, which were thought to belong to different subfamilies with tetraploid Percocypris fishes in morphology, but they are sister genera in molecule. Fortunately, the pentaploid hybrid fishes have been successfully obtained by hybridization of Schizothorax wangchiachii (♀, 2n = 6X = 148) × Percocypris pingi (♂, 2n = 4X = 98). To understand the genetic and morphological difference among the hybrid fishes and their parents, four methods were used in this study: morphology, karyotype, red blood cell (RBC) DNA content determination and inter-simple sequence repeat (ISSR). In morphology, the hybrid fishes were steady, and between their parents with no obvious preference. The chromosome numbers of P. pingi have been reported as 2n = 4X = 98. In this study, the karyotype of S. wangchiachii was 2n = 6X = 148 = 36m + 34sm + 12st + 66t, while that the hybrid fishes was 2n = 5X = 123 = 39m + 28sm + 5st + 51t. Similarly, the RBC DNA content of the hybrid fishes was intermediate among their parents. In ISSR, the within-group genetic diversity of hybrid fishes was higher than that of their parents. Moreover, the genetic distance of hybrid fishes between P. pingi and S.wangchiachii was closely related to that of their parental ploidy, suggesting that parental genetic material stably coexisted in the hybrid fishes. This is the first report to show a stable pentaploid F₁ hybrids produced by hybridization of a hexaploid and a tetraploid in aquaculture.     

荧光原位杂交技术(FISH)在鱼类遗传学研究中的应用及前景

荧光原位杂交技术（ｆｌｕｏｒｅｓｃｅｃｅｉｎｓｉｔｕｈｙｂｒｉｄｉｚａｔｉｏｎ,ＦＩＳＨ）是一种在分子水平上进行了细胞遗传学研究的得力工具,本文综述了近年来ＦＩＳＨ技术在鱼类的基因定位,性别鉴定,染色体变异及种间杂交等研究中的应用;并将此技术在鱼类的基因定位,早期性别鉴定,染色体重排与进化,染色体鉴别与分类及杂交鉴定等方面的应用前景作一展望。     

Diversified chromosomal characteristics in Centropyge fishes (Pomacanthidae, Perciformes)

We studied karyotypes and other chromosomal markers such as C-banded heterochromatin and Ag-stained nucleolus organizer regions (Ag-NORs), in seven Centropyge fishes (Pomacanthidae, Perciformes). These results revealed diversified chromosomal characteristics in Centropyge species. Three species had 2n = 48 chromosomes, whereas four species had 2n = 52 chromosomes. Fundamental numbers showed a large variation from 48 to 82, particularly in the species with 2n = 52 chromosomes. In all the species, Ag-NORs were located in a single chromosome pair and C-bands were mainly distributed in the centromeric regions of most chromosomes, as commonly seen in teleostean fishes. However, these chromosomal markers showed species-specific variations and provided us with useful information that could help us in understanding chromosomal evolution. On the basis of these chromosomal characteristics, we infer the process of chromosomal evolution, which according to us involves an increase in chromosome number from 2n = 48 to 2n = 52 through centric fission or other mechanisms, and in fundamental number through pericentric inversion. In particular, karyotypic evolution involving the increase in chromosome number is an unusual event in the evolution of higher teleostean groups. Handling editor: K. Martens     

Turnover of sex chromosomes and speciation in fishes

Closely related species of fishes often have different sex chromosome systems. Such rapid turnover of sex chromosomes can occur by several mechanisms, including fusions between an existing sex chromosome and an autosome. These fusions can result in a multiple sex chromosome system, where a species has both an ancestral and a neo-sex chromosome. Although this type of multiple sex chromosome system has been found in many fishes, little is known about the mechanisms that select for the formation of neo-sex chromosomes, or the role of neo-sex chromosomes in phenotypic evolution and speciation. The identification of closely related, sympatric species pairs in which one species has a multiple sex chromosome system and the other has a simple sex chromosome system provides an opportunity to study sex chromosome turnover. Recently, we found that a population of threespine stickleback (Gasterosteus aculeatus) from Japan has an X₁X₂Y multiple sex chromosome system resulting from a fusion between the ancestral Y chromosome and an autosome, while a sympatric threespine stickleback population has a simple XY sex chromosome system. Furthermore, we demonstrated that the neo-X chromosome (X ₂) plays an important role in phenotypic divergence and reproductive isolation between these sympatric stickleback species pairs. Here, we review multiple sex chromosome systems in fishes, as well as recent advances in our understanding of the evolutionary role of sex chromosome turnover in stickleback speciation.     

On the karyosystematics of cyprinid fishes and a summary of fish chromosome studies in China

To date, the chromosomes of 210 species of fresh-water fishes have been studied in China. They are principally cyprinids. Based upon the karyotypic data so far obtained mainly by the authors' laboratory, a report is here submitted on the karyosystematics of Chinese cyprinid fishes.The primitive karyotype of cyprinid fishes may be inferred as being 2n=50. During phyletic evolution the cyprinid fishes probably have been differentiated into two large branches, one of which with the Leuciscinae as a basic group and another branch with the Barbinae as a basic group. As to the modes of their chromosome evolution, Robertsonian translocation seems to be prominent in the first branch, whereas polyploidization appears to be prominent in the second branch. Based on the chromosome studies in cyprinid fishes, some tentative ideas about the classification of the subfamilies in Cyprinidae are presented.A table containing the karyotypes of Chinese fresh-water fishes is attached.This work was partially supported by the Science Fund of the Chinese Academy of Science.     

中国鲤科鱼类染色体组型的研究 Ⅱ.鲴亚科四种鱼的染色体组型

鲴亚科(Xenocyprininae)鱼类多为中小型鱼类,常见于江河湖泊等较宽阔的水域中,我国长江、黑龙江、黄河及珠江诸流域皆有分布,共有10种,隶属4个属(伍献文等,1964)。迄今尚未见有该亚科鱼类染色体组型的研究报道。本文是对其中三属四种鱼的染色体组型的观察结果。这四种鱼是银鲴(Xenocypris argentea)、黄尾鲴(Xenocypris davidi)、细鳞斜颌鲴(Plagiognathops microlepis)和逆鱼(Acanthobrama simoni)。其中黄尾鲴和细鳞斜颌鲴均为新的淡水养殖鱼(沈德长等,1981;陈楚星,1979)。     

鲀形目3种鱼的染色体组型分析

采用胸腔注射植物血球凝集素(phytohemagglutinin,PHA)及秋水仙素溶液,取活体头肾细胞经低渗、固定、空气干燥法,分析比较了中华单角鲀(Monacanthus chinensis)、黄鳍东方鲀(Takifuguxanthopterus)、红鳍东方鲀(T.rubripes)的核型。结果表明,3种海水鱼中期染色体均为二倍体,未发现异型性染色体、随体和次缢痕。其核型如下:中华单角鲀的核型为2n=34(34t),臂数:NF=34;黄鳍东方鲀的核型为2n=44(12m+8sm+24t),臂数:NF=64;红鳍东方鲀的核型为2n=44(14m+6sm+24t),臂数:NF=64。中华单角鲀的核型与后两者存在较大差异。同时,将此3种鱼的核型与前人报道的其他鲀形目鱼类核型作了比较。     

Karyotype of the Snow Sculpin <Emphasis Type="Italic">Myoxocephalus brandti</Emphasis> Steindachner (Cottidae) from Peter the Great Bay,Sea of Japan

The karyotype of the snow sculpin Myoxocephalus brandti, 2n = 44, NF = 46, from Peter the Great Bay was studied. Two-armed chromosomes were presented by one pair of metacentric chromosomes of medium size; one-armed chromosomes included two pairs of large subtelocentric chromosomes and a pair of large acrocentric chromosomes. Ag-NOR-staining in the telomere vicinity revealed nucleolus-organizing regions in one metacentric chromosome and in one medium size acrocentric chromosome in one of the fishes, in two homological small acrocentric chromosomes in three fishes, and in one acrocentric chromosome of average size in six fishes. No difference between the male and female karyotypes and any type of variability was revealed. The karyotypes of the snow sculpin M. brandti and the frog sculpin M. stelleri were compared. Their distinctions and similarities were displayed.Original Russian Text Copyright ¢ 2005 by Biologiya Morya, Ryazanova.     

Cytology and systematica of Araceae

The chromosome numbers of 75 species belonging to the family Araceae have been determined. The numbers for 53 species are reported for the first time. One number differs from previous reports ( Aglaodorum ), and one number is corrected (Phymatarum). Within 15 genera ( Gymnostachys, Pothoidium, Alloschemone, Heteropsis, Holochlamys, Anaphyllopsis, Dracontioides, Pseudohydrosme, Montrichardia, Bucephalandra, Taccarum, Asterostigma, Gorgonidium, Spathantheum and Ulearum ) the chromosome numbers have not previously been determined. The total number of genera cytologically investigated is now 99 (c. 94%).
A great diversity in chromosome numbers as well as in chromosome size and constitution is found. The results are discussed in relation to the phylogeny and the previously published classifications of the family.
A total list of chromosome numbers counted (>700 species) in the Araceae is presented (Appendix).     

An unusual ZZ/ZW sex chromosome system in Characidium fishes (Crenuchidae, Characiformes) with the presence of rDNA sites

Characidium fishes with a sex chromosome system form a monophyletic group. This work presents data of Characidium lanei from the South Atlantic basin (Brazil), including an unknown type of ZW sex chromosome system for the groups including the presence of rDNA sites on sex chromosomes.     

Comparison between community structures of fishes in <Emphasis Type="Italic">Enhalus acoroides</Emphasis>- and <Emphasis Type="Italic">Thalassia hemprichii</Emphasis>-dominated seagrass beds on fringing coral reefs in the Ryukyu Islands,Japan

To clarify differences in community structures and habitat utilization patterns of fishes in Enhalus acoroides- and Thalassia hemprichii-dominated seagrass beds on fringing coral reefs, visual censuses were conducted at Iriomote and Ishigaki islands, southern Japan. The numbers of fish species and individuals were significantly higher in the E. acoroides bed than in the T. hemprichii bed, although the 15 most dominant fishes in each seagrass bed were similar. Cluster and ordination analyses based on the number of individuals of each fish species also demonstrated that fish community structures were similar in the two seagrass beds. Species and individual numbers of coral reef fishes which utilized the seagrass beds numbered less than about 15% of whole coral reef fish numbers, although they comprised about half of the seagrass bed fishes. Of the 15 most dominant species, 5 occurred only in the two seagrass beds, including seagrass feeders. Ten other species were reef species, their habitat utilization patterns not differing greatly between the two seagrass beds. Some reef species, such as Lethrinus atkinsoni and L. obsoletus, showed ontogenetic habitat shifts with growth, from the seagrass beds to the coral areas. These results indicate that community structures and habitat utilization patterns of fishes were similar between E. acoroides- and T. hemprichii-dominated seagrass beds, whereas many coral reef fishes hardly utilized the seagrass beds.     

人类性染色体特异ＤＮＡ对三种鱼类染色体的描绘

染色体描绘是研究基因组进化的强有力手段之一,用人Ｘ和Ｙ染色体文库特异ＤＮＡ为探针,对３种硬骨鱼类－刺鳅、黄鳝和斑马鱼的有丝分裂中期裂染色体进行了描绘研究,结果表明,在这３种鱼类的染色体组中都发现有人Ｘ染色体特DN的同源片段,它们散布在几对同源染色体中,但用人Ｙ染色体ＤＮ描绘这３种鱼类染色体时,则没有检测出可见的同源片段。同时对从低等脊椎动物到人类的Ｘ染色体进化过程进行了进一步探讨。     

蕨类植物染色体数目研究的好材料

染色体数目分析是现代系统与进化植物学研究十分重要和不可缺少的环节.在蕨类植物中,使用根尖或孢子母细胞作为实验材料的经典方法在取样时往往存在困难.该文以3种桫椤科桫椤属植物为例,探寻适合蕨类植物染色体数目研究的材料.由于取样时没有时间、季节和数量上的限制,我们推荐配子体作为蕨类植物染色体数目研究的实验材料.     

A Novel ZZ/ZW Sex Chromosome System for the Genus Leporinus (Pisces, Anostomidae, Characiformes)

A wide range of sex chromosome mechanisms, including simple and multiple chromosome systems is characteristic of fishes. The Leporinus genus represent a good model to study sex chromosome mechanisms, because an unambiguous ZZ/ZW sex chromosome system was previously described for seven species, while the remaining studied species of the genus do not show differentiated sex chromosomes. The occurrence of sex chromosomes in Leporinus trifasciatus and Leporinus sp2 from the Araguaia river, Amazon basin, Brazil, was here investigated. ZZ/ZW sex chromosomes were detected for both species. The Z and W chromosome morphology of L. trifasciatus is the same as described for other species of the genus Leporinus. However, the Z and W chromosomes of L. sp2 were quite different in their morphology and banding pattern suggesting that the ZW system of this species have originated independently from the ZW system previously described for other Leporinus.     

Assessing Genetic Diversity of Brazilian Reef Fishes by Chromosomal and DNA Markers

Little is known on genetics of Brazilian coral reef fish and most of this information is limited to chromosome characterization of major representative species. The diploid chromosome number in marine fish varies from 2n= 22–26 to 2n = 240–260. Despite of this apparent diversity, most studied marine species have a diploid complement with 48 acrocentric chromosomes. This latter trend is mostly observed among Perciformes, an important major taxon of coral reef fishes. Studies in the families Pomacentridae, Pomacanthidae and Chaetodontidae, for example, have shown a common karyotype pattern entirely formed by 48 uniarmed chromosomes. However, rare numerical and structural chromosome polymorphisms and cryptic chromosome rearrangements involving heterochromatin segments and/or nucleolar organizing sites have been reported among such fishes. Although new chromosome forms can contribute to the establishment of genetically isolated populations, their role in reef fish speciation at marine realm still is an open question. More recently, genomic DNA analyses using RAPD and microsatellites, and sequencing and RFLP of mitochondrial DNA have increasingly been used in Atlantic reef fish species. Genetic homogeneity over wide geographical ranges has been reported for different fish groups, in contrast to several cases of population substructuring related to environmental constraints or evolutionary history. Amazonas outflow and upwelling on the Southeastern coast of Brazil are believed to be strong barriers to dispersal of some reef species. Moreover, it is suggested that the pattern of speciation and population structure at South Atlantic is quite distinctive from Pacific Ocean, even when comparing closely related taxa. Further genetic studies are strongly encouraged in Brazilian reef fishes in order to provide a reliable scenario of the genetic structure in this important and diverse fish group.