Chromosome morphology and species evolution in the five north American species of pacific salmon (Oncorhynchus)

Assignment of Chinook salmon (Oncorhynchus tshawytscha) linkage groups to specific chromosomes reveals a karyotype with multiple rearrangements of the chromosome arms of rainbow trout (Oncorhynchus mykiss)

The Chinook salmon genetic linkage groups have been assigned to specific chromosomes using fluorescence in situ hybridization with bacterial artificial chromosome probes containing genetic markers mapped to each linkage group in Chinook salmon and rainbow trout. Comparison of the Chinook salmon chromosome map with that of rainbow trout provides strong evidence for conservation of large syntenic blocks in these species, corresponding to entire chromosome arms in the rainbow trout as expected. In almost every case, the markers were found at approximately the same location on the chromosome arm in each species, suggesting conservation of marker order on the chromosome arms of the two species in most cases. Although theoretically a few centric fissions could convert the karyotype of rainbow trout (2N = 58–64) into that of Chinook salmon (2N = 68) or vice versa, our data suggest that chromosome arms underwent multiple centric fissions and subsequent new centric fusions to form the current karyotypes. The morphology of only approximately one-third of the chromosome pairs have been conserved between the two species.

Evolution of duplicated growth hormone genes in autotetraploid salmonid fishes

A defining character of the piscine family Salmonidae is autotetraploidy resulting from a genome-doubling event some 25-100 million years ago. Initially, duplicated genes may have undergone concerted evolution and tetrasomic inheritance. Homeologous chromosomes eventually diverged and the resulting reduction in recombination and gene conversion between paralogous genes allowed the re-establishment of disomic inheritance. Among extant salmonine fishes (e.g. salmon, trout, char) the growth hormone (GH) gene is generally represented by two functional paralogs, GH1 and GH2. Sequence analyses of salmonid GH genes from species of subfamilies Coregoninae (whitefish, ciscos) and Salmoninae were used to examine the evolutionary history of the duplicated GH genes. Two divergent GH gene paralogs were also identified in Coregoninae, but they were not assignable to the GH1 and GH2 categories. The average sequence divergence between the coregonine GH genes was more than twofold lower than the corresponding divergence between the salmonine GH1 and GH2. Phylogenetic analysis of the coregonine GH paralogs did not resolve their relationship to the salmonine paralogs. These findings suggest that disomic inheritance of two GH genes was established by different mechanisms in these two subfamilies.

Chromosomal characterization of cultured populations of Chilean coho salmon (Oncorhynchus kistuch)

Chromosomal characterization of coho salmon samples from three fish farms in southern Chile (Polcura, Castro and Coyhaique) was carried out in order to compare their chromosome constitutions. All populations had a 2n = 60; however, Polcura and Coyhaique had a different chromosome arm number (NF = 110; 40m + 10sm + 10st/t) than Castro (NF = 108; 40m + 8sm + 12st/t). Variation in NF was due to chromosome pair 25, which was submetacentric in Coyhaique and Polcura, but subtelocentric in Castro. In all karyotypes, a large submetacentric chromosome pair exhibited an interstitial secondary constriction in the short arm. The observed variability in chromosome arm number agrees with previous reports for O. kisutch, and in this particular case it seemed to be caused by a pericentric inversion of pair 25. Cultured populations of Chilean coho salmon are, therefore, likely to be cytogenetically variable.

DNA homologies between the rainbow trout, chum salmon and coho salmon

The thermal stabilities of hybrid duplexes between the DNAs from three salmonid fish species were monitored as measures of DNA homology. The chum salmon, Oncorhynchus keta, and coho salmon, Oncorhynchus kisutch, had more DNA homology with each other than either had with the rainbow trout, Salmo gairdnerii. Morphological, ecological and protein similarities between the coho salmon and the rainbow trout may be due to parallel or convergent evolution.

Fish cell lines: Establishment and characterization of nine cell lines from salmonids

Nine permanent cell lines have been established from five species of salmonids native to America's Pacific Northwest. With the exception of a hepatoma from an adult trout, the lines were derived from normal tissues of embryonic or juvenile fish. Cells were routinely grown in Eagle's minimum essential medium with 10% fetal bovine serum. Optimum growth temperatures for these lines ranged from 21 to 24 degrees C. All survived storage for at least 1 yr at -65 degrees C and at least 5 yr in liquid nitrogen. Six of the lines were demonstrably free of any microbial contamination but mycoplasmas were found in three. Eight of the lines were heteroploid. The morphology of only one was fibroblastic. All the lines effectively replicated one or more of the common salmonid viruses. Isozyme patterns were consistent with those of the species of origin. These cell lines have significant application in fish virology.

Chromosome relationships in the genus Salmo

Chromosome numbers and polymorphisms in rainbow trout, Atlantic salmon, and brown trout are described. The karyotypes of these three species are compared with each other and with those of other salmonid fish from the genera Salmo, Salvelinus, and Oncorhynchus. Karyotype evolution from a postulated ancestral tetraploid is discussed.

Sex chromosomes in the sockeye salmon: a Y-autosome fusion

Chromosomes of 21 sockeye salmon [Oncorhynchus nerka (Walbaum)] from three locations in Washington state were examined. All males had 57 chromosomes, while all females had 58 chromosomes. Both sexes had 104 chromosome arms. It appears that in males of this species the Y chromosome and an autosome have fused to form a metacentric chromosome.

Heteromorphic sex chromosomes in male rainbow trout

A pair of subtelocentric chromosomes differs in the size of the short arm in male, but not female, rainbow trout (Salmo gairdneri). The morphological similarity of the X and Y chromosomes, and the observation of Y chromosomes intermediate between the X and normal Y, suggest that the sex chromosomes are at an early stage of differentiation in this species.

Cytogenetic studies of Poecilia (Pisces). I. Chromosome numbers of naturally occurring poeciliid species and their hybrids from Eastern Mexico

Cytological studies of fish from the subgenus Poecilia (Pisces) including members of an all-female species, P. formosa, have clearly shown diploid, somatic chromosome complements and Robertsonian arm numbers of 46. A triploid somatic chromosome complement of 3N = 69 was demonstrated for members of a naturally occurring variant clone of P. formosa, a form whose general body morphology closely resembles that of its sympatric species P. mexicana. Chromosomes of the different poeciliid species studied are remarkably similar in size, shape and structure, being mostly short acrocentrics, 2 μ long or less.The presence of a chromosome bearing a sub-terminal centromere within the complement of the Amazon molly provides the only direct evidence to date of centric shifts within the chromosome complement of the subgenus Poecilia. This finding also provides the first plausible cytogenetic basis for concluding that P. formosa is of relatively recent origin. Comparisons of relative chromosome lengths from both mitotic and meiotic configurations of related species indicate that the heteromorphic chromosome pair of P. formosa probably was derived by hybridization between P. latipinna and P. mexicana. Finally, as suggested by the numbers and forms of chromosomes in atypical, triploid specimens of P. formosa, their complements apparently contain both a maternal diploid set of chromosomes from the all-female species, and a paternal haploid set of chromosomes from P. mexicana.